CIMO WG UpperAirM 1999

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CIMO WG UpperAirM 1999 Powered By Docstoc


               WORKING GROUP

                     New Delhi, India

                   6 - 10 December 1999

                  FINAL REPORT

     1.1 Opening of the meeting
     1.2 Working arrangements
     1.3 Adoption of the agenda
     2.1 Progress report of the chairman
     2.2 Working procedures for the intersessional period
     2.3 Evaluation of working progress
     2.4 Participation of manufacturers at meetings
     2.5 National progress reports
     2.6 Y2K status
     3.1 Report of the Rapporteur on Radiosonde Compatibility Monitoring
     3.2 Quality assurance of the radiosonde observing system
         3.2.1 Quality assurance during the production
         3.2.2 Laboratory evaluations and calibrations
         3.2.3 Training of operators
         3.2.4 Pre-flight quality checks
         3.2.5 Results from national / bilateral comparisons
     3.3 Review of data quality, including relative humidity measurements
     3.4 Status of GPS windfinding systems
     3.5 Coding issues including the input of surface observations and a plan for moving from
         TEMP code to BUFR
     3.6 Testing output from algorithms using standard data sets
     3.7 Review of automatic radiosonde launch systems
     3.8 Recommendations from the Expert Meeting on Operational Issues for Radiosonde
         Applications in the Tropics and Sub-tropics
     3.9 Priorities for future radiosonde developments


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1.1 Opening of the session
     The session of the Working Group on Ground-based Upper-air Observing Systems (further
called Working Group) was held at the Hotel Samrat in New Delhi, India, from 6 to 10 December
1999 on kind invitation of the India Meteorological Department (IMD). The lists of participants and
their addresses are attached as Appendices A and B to this report.
     The meeting was opened on Monday, 6 December 1999 at 10.00 a.m. by Dr R.R. Kelkar,
Director-General of Meteorology of IMD and Permanent Representative of India with WMO. He
welcomed the participants and noted IMD’s pleasure in hosting the session. He referred to the
importance of considerations and exchange of experience in the field of upper-air in-situ and
remote measurements and briefly informed on the work done by India in both areas. Dr Kelkar
underlined that the conventional radiosonde measurements will remain, for many years to come,
the backbone of the upper-air observation network. In this regard, he draw attention to the
extended network of upper-air stations operated by IMD and to the fact that approximately 30,000
radiosondes were manufactured per annum within an IMD owned factory established for this
purpose.      He reiterated the importance of continued operation of radiosonde stations
notwithstanding cost pressures although there were possible alternatives including profilers,
Doppler radar, and satellite systems which might be considered as suitable means for replacement
of in-situ observations in the future. He urged the Working Group to seek solutions for overcoming
some difficult problems in radiosonde operation in India, mainly related to improving the quality of
observations. He offered any support and hospitality to participants and wished them every
success within the session and a nice stay in New Delhi.
      Dr S.K. Srivastava, President of CIMO and Additional Director-General of Meteorology within
IMD, emphasised in his statement the need for a strong observing system and for high quality
observations as a requirement for all applications. He underlined that homogeneity of data was a
critical issue, which needed serious considerations of all concerned but especially of CIMO
experts. He underlined that IMD had learned the importance of standardisation and calibration
through own experience and will support all efforts in this regard. He urged participants to focus
their efforts on solutions and recommendations in this regard and offered his total support in his
position in IMD as well as President of CIMO.
      Dr J. Nash (UK), Chairman of the Working Group, thanked Dr Kelkar personally and the IMD
for hosting the meeting. He saw it as an opportunity to bolster collaboration between countries
around the world and especially as a significant contribution to the Global Observing System GOS.
He suggested that quality of work and operations was important for consideration at the session.
He hoped that experts from India, who attend the session either as member of the WG or as
observers, could discuss matters of their concern and interact with the Working Group. Dr Nash
sought bridge building between many countries to work effectively as a group to develop systems
for the future. He welcomed the representatives of manufacturers and saw their participation as
valuable. Co-operation between National Meteorological Hydrological Services (NMHSs) and
manufacturers was essential and processes need to be considered to develop and make that
interaction effective. He underlined in this regard that data accuracy was important since for
example study of long-term changes in climate research required highly accurate data. He
expressed a general sentiment that constructive criticism was very important to help improve
systems. He finally referred briefly to some interesting topics of the Agenda for consideration. He
invited experts to express their personal views and inform on their countries’ requirements.
     Mr K. Schulze welcomed as representative of the WMO Secretariat the participants in New
Delhi and conveyed the best wishes and the gratitude from Professor G.O.P. Obasi, Secretary
General of WMO, to the delegates. He expressed his gratitude to India for its invitation to organise
the session. He appreciated the efforts of Members of WMO to enable experts to participate and
also that of several manufacturers of upper-air equipment for attendance of their representatives.
The main purpose of inviting the latter is that Members requirements needed to be communicated
effectively to manufacturers through WMO bodies, such as this Working Group. CIMO was a good
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vehicle for example to promote this important interaction. Mr Schulze emphasised that work of
CIMO was the basis for quality of observations - many programmes and data users relied critically
on the data quality. He, however, expressed his concern that the number of instrument experts still
available for this important work seemed to be decreasing and no matter what the future of CIMO
might be the work on instruments and quality has to be continued by WMO through experts’ work.
Finally, he underlined that the most important objective of this Working Group session was to
precisely define its work programme based on the terms of reference given by CIMO-XII and to
allocate the tasks for the next two years to the experts concerned in noting that CIMO will meet in
2002. He wished the session every success in its work.
1.2 Adoption of the agenda
     The Chairman briefly introduced the Provisional Agenda and invited the participants for
providing comments. Dr Griersmith raised the issue of Y2K problem, which was not yet reflected
within the Provisional Agenda, and it was agreed it would briefly be addressed under Agenda
Item 2.6. The session then adopted the Agenda as basis for its work with the understanding that it
could be amended during the session, if necessary. The final agenda can be found in front of this
1.3 Working arrangements for the session
      The session determined its working hours and the participants were informed on the local
arrangements necessary for carrying out the session. English was selected the working language
for the session.


2.1 Progress report of the chairman
     The chairman underlined that this first session of the Working Group after already more than
one year since the CIMO XII passed is of high importance for accomplishing the work. Dr Nash
highlighted in his progress report on the work done so far especially issues of radio frequency
allocation and his own work in that area: this could have a big potential impact on future operations
of Services (e.g. on upper-air observations). He underlined that several Member countries have
not yet fully recognised the real potential impact of it. Several radio frequency bands are
threatened, such as the 400-406 MHz band where there was tremendous pressures for its
application for mobile satellite services (MSS).
     Dr Nash underlined that another area of relevance to the Working Group was the ongoing
studies on the upper-air component of the GOS, which require close collaboration with CBS.
There was a strong view that a CBS representative preferably from one of CBS’s Open
Programme Area Groups (OPAG) should take part in the further activities of the Working Group. It
was noted that Dr Griersmith, Bureau of Meteorology of Australia (BOM), agreed to communicate
relevant matters to Mr A. Sharp (also BOM) who was involved in the work of CBS related to
representing upper-air systems in the study related to the redesign of the GOS.
   Finally to this agenda item, the chairman expressed his appreciation to members of the
Working Group and especially to the rapporteurs for the valuable contributions already provided.
2.2 Working procedures for the intersessional period
    The chairman drew the attention to the fact that the establishment of effective communication
mechanism for exchanging information between the chairman and members of the Working Group
is the most important measure besides the allocation of tasks to experts for getting the
comprehensive work done best. In this connection it has to be taken into account that no further
session of the Working Group can be convened prior to CIMO-XIII due to serious financial
constraints while latter is planned to be held in autumn 2002.
     In referring to Document 9 (Draft Work Plan for the Working Group), Dr Nash outlined some of
the key issues pertaining to the primary task, and underlined that by end of 2001 major information
and work results must be prepared to meet the needs for submission of documents for CIMO-XIII.
He specifically highlighted in this regard that one overall aim of the work was to get the quality of
radiosonde or ground-based upper-air data improved globally to better meet the increased
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requirements of users. For achieving this objective best, new concerted efforts needed to be
     In further considering how the Working Group could conduct its business within the
intersessional period, the meeting was informed that the holding of expert meetings with limited
participation might still be a possible and suitable means for tackling current problems. However,
such a meeting could be organised only if budgetary savings could be made available in WMO and
when a strong justification can be given. An example in this regard was the recently organised
Expert Meeting on Radiosonde Applications in the Tropics held in Geneva. The meeting noted that
there was a strong requirement for better interaction with manufacturers of radiosondes at a time
when many new products were being introduced, and when many changes were taking place in
ground systems and operational procedures. A meeting once every four or five year with the
relevant WMO experts seemed an inadequate method of interaction.
     Dr Nash indicated that a good collaboration of the members of the Working Group, which
includes all rapporteurs, with the chairman on one hand as well as between the experts on the
other hand, is an essential precondition for the success of the work. This includes the regular
exchange of information, the submission of outlines for contributions, and of reports for further
considerations and improvement. It was informed that the concise documents, which have to be
prepared for submission to CIMO-XIII, could reflect the working results of the group in a very
limited manner only due to the significant limitation in words permitted for these contributions1.
Furthermore it was noted with concern that only CIMO members and potential delegates of
CIMO XIII would have access to these documents which do not have any official status after the
commission session, since their contents will not be reflected in its Final Report. In considering
this, it was agreed that in addition to these CIMO-XIII documents more comprehensive reports
should be prepared, which would reflect valuable output of the work in greater detail. They should
be related to specific fields of interest as requested within the terms of reference of the Working
Group or related to actual issues of common concern. These reports could be published within
WMO’s Instruments and Observing Methods Report series (IOM series) and should, in addition, be
put on WMO’s Web Home Page for general access. Furthermore, it should be considered to also
publish them after an editing process in an appropriate scientific journal, if their content is of more
general interest. Related to this, the Working Group considered whether some of the documents
prepared for the WG session might already be suitable for this purpose after a review, such as
Document 16 prepared by Mr Mannoji on GPS derived precipitable water content. (See relevant
decisions of the Working Group as reflected further down in this report.)
       Mr Mannoji: Preparation of a IOM publication on GPS derived water vapour content M1

    In this regard the WG also noted with interest that there were already several nationally
prepared reports of common interest available which contain valuable information, such as on
radiosonde comparisons carried out nationally. If, for various reasons, these reports cannot be
published by WMO, it was proposed to create a Hyperlink from WMO’s Web page to such reports,
which have to be put on the related national Web page for making them accessible to a wider
2.3 Evaluation of working progress
     Based on the currently available working results and objectives, consideration were made
towards enhancing the effectiveness of the work of the Working Group in view of the capacities
and capabilities of their individual members. In this regard, Dr Nash suggested a target of
improving compatibility of radiosonde data and integration with other observing systems such as
aircraft and remote sensing. Related to this, he mentioned his concern that there were problems in
getting the final report completed for the last WG established at CIMO-XI which was also chaired
by him. because of a poor flow of information from WG members. This problem has to be avoided
in the working mechanism used in the intersessional period between the Commission sessions.

    The strong limitation of words is caused by significantly reducing the high translation costs because all
     documents for commission sessions have to be made available in English, French, Spanish, Russian,
     Arabic, and Chinese languages.
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2.4 Participation of manufacturers at sessions
    The Working Group highly appreciated that representatives of 7 manufacturers of upper-air
equipment attended the session during the first three days. The chairman invited reports and
comments from these manufacturers.
         Mr Hoerhammer (Vaisala, Finland) cited two key issues, namely there was a need to
          improve communication of manufacturing requirements and feedback was required
          especially on the operation of GPS radiosondes related to wind data. He was concerned
          that the manufacturers could obtain access to all TEMP reports from their systems. He
          underlined that the ECMWF quality monitoring system has potential to give data on
          performance of radiosondes. He further underlined that about 75-80% of TEMP reports is
          already available on the Web. He noted with appreciation the approach of the NWS of the
          USA, as reflected in Appendix F of Doc. 3.
         Dr Kats (KOMET, Russian Federation) informed that KOMET was established on the
          basis of Central Aerological Observatory (CAO) in 1996 by Roshydromet mainly for
          producing radiosondes to be applied within the Russian upper-air network mainly
          equipped with modernised AVK ground stations. Specialists of KOMET still continued
          research activities in upper-air measurements, including calibration and testing, especially
          for humidity measurements.
         Mr Curran (Sippican/VIZ, USA) raised several issues. User requirements were often
          defined by each client, and so varied to an unnecessary extent, which could lead to an
          increase in the cost of the product. He underscored that user behaviour was sometimes
          very problematic. He urged CIMO to continue defining uniform requirements for general
          application as far as needed. He underlined that feedback to manufacturers was
          important and the already established good relation with CIMO’s upper-air experts should
          be enhanced. In partly responding, Mr Bower drew attention to an ensuing discussion by
          suggesting that standard for contracts and warranty compliance conditions would help as
          already applied by some Services.
         Mr Naaman (Metatron, Israel) highlighted the information contained in Document 6 on the
          actual performance of operational radiosonde stations in specifically noting that GPS
          radiosonde performance was not yet satisfactory. He underlined that more attention of
          Members should be directed to the application radiotheodolites as a viable alternative
          within some climatic regions3.
         Mr Parini (InterMet Systems, USA) said the minimum requirement for radiosonde systems
          should be articulated as part of a basic system requirement. If users’ requirements
          increase, the recommendations should be specified so that manufacturers meet those
         Mr Pepin (Geolink, France) informed that they had a new generation radiosonde system
          was available for testing.
    Resulting from related discussion on standards and quality including the need expressed by
representatives of manufacturers it was agreed that interface standards for various components
should be better articulated.
     At a specific short side meeting with the representatives of manufacturers 4 which was held on
invitation of and chaired by the Dr Srivastava, President of CIMO, with attendance of Mr D.C.
Schiessl, Director for Basic Systems within the WMO Secretariat, the outcomes of the collaboration
between WMO and manufacturers was reviewed and proposals developed on how to proceed best
in this regard. The concise report of this meeting was prepared separately and was made
available to those concerned.

  See List of Attendance as provided in Appendix A
  This issue will be reconsidered later in the agenda.
  Convened on Wednesday, 8. 12. 1999, in the afternoon.
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2.5 National progress reports
    All members of the Working Group provided reports on issues related to the national upper-air-
observing network more comprehensively reflected in the documents submitted to the session but
concisely summarised below, as follows:
       CHINA
        The upper-air network of CMA operates 89 stations, with most of them using a secondary
        wind finding radar at 403 MHz. Because this radar sounding system was developed in the
        1960s already, the technique does not provide measurements of fully satisfactory accuracy.
        In order to solve this problem, CMA began in 1990 to develop a new upper-air sounding
        system based on two different radar types. One was working in the C-band but due to
        serious frequency interference related to the radiosonde, it could not be introduced for
        operational use. Therefore a secondary radar system working in the L-Band (1680 MHz)
        was developed and prototypes are now under test with the objective to begin the
        operational introduction within the next 2 to 3 years.
       USA
        The National Weather Service of the USA (NWS) supports 102 rawinsonde sites situated in
        the contiguous United States and Alaska, the Pacific Islands, as well as in the Caribbean
        Co-operative Hurricane Upper-air Network. Sixteen sites are designated as part of the
        GCOS Upper-air Network (GUAN). The NWS uses radiosondes manufactured by Vaisala
        and Sippican Meteorological System Group (formerly VIZ). Radiosondes from both
        radiosonde vendors are deficient in the measurements of relative humidity (RH). Vaisala
        has changed the desiccant used in packaging to reduce outgassing contamination and the
        subsequent RH dry bias. Sippican has continued efforts to improve the manufacturing
        process and has introduced additional calibration coefficients to improve sensor accuracy.
        Operational practices, such as radiosonde pre-flight checking procedures, disposition of
        faulty radiosondes, and operation data quality assurance activities were outlined. The NWS
        reported on Y2K readiness activities and on the status of the U.S. LORAN-C network.
        Furthermore, the session was informed on procurement activities for a new radiosonde
        system to replace its Radio-direction Finding System (over 40-years old). The new system
        will be a 1680 MHz radiosonde system. The system and GPS radiosondes are scheduled
        for initial implementation in late 2001 and implementation should conclude by 2004. The
        US National Centres for Environmental Prediction will receive high resolution 1 to 2 second
        data, with associated latitude, longitude, time, and height data for application in forecast
       South Africa
        South Africa operates 12 upper-air stations, including remote sites on Marion Island and
        Gough Island. All these stations previously used the OMEGA system, but since the
        termination of this system, they have all changed to GPS radiosondes, (Vaisala RS80-15G)
        with the DigiCora ground equipment.
        A large number of ascents produced no winds or had significant gaps in the wind profile.
        The radiosonde manufacturer sent a representative to South Africa, and conducted tests to
        determine the cause of these failures. Results showed that the majority of the radiosondes
        failed due to the so-called “Intermediate Frequency (IF) drift problem”. Some flights failed
        due to poor launching techniques. Vaisala has provided new software to address the IF
        drift problem, as well as is prepared making changes to some of the electronic components
        of the radiosondes. It was also recommended that all radiosondes be ground-tested to
        ensure that sufficient satellites are received by the radiosonde and that operators be
        instructed to use the proper launch technique. The introduction of these changes have
        improved the quality of the data, although the radiosondes in use are not yet of the new
        type (post-May 1999). A number of radiosondes are being rejected at ground level, and the
        manufacturer has undertaken to replace radiosondes, which are unable to receive signals
        before launch.
        Due to the high cost of the GPS radiosondes, which is further aggravated by foreign
        currency exchange rates, as well as budgetary constraints, South Africa has been forced to

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        drastically reduce the number of GPS radiosondes used, and to make use of the cheaper
        PTU only radiosonde combined with winds obtained by optical theodolite.
       Egypt
        The Egyptian Meteorological Authority (EMA) operates 4 upper-air stations. Three of them
        have been performing observations twice daily for more than 40 years while the fourth
        station was established in 1996. Since 1995 all stations were equipped with radiotheodolite
        systems (1680 MHz). The TEMP as well as CLIMAT TEMP messages are automatically
        generated and transmitted to the HQ in Cairo for further checking and quality control before
        feeding them into the GTS. All systems are tested and proved to be Y2K compliant. EMA
        is planning to enhance its upper-air network by another two similar systems up to 2002.
       India
        India Meteorological Department is operating a network of 34 RS/RW and one RS station.
        Presently a IMD-MK III radiosonde is used, equipped with an aneroid-based baroswitch, rod
        thermistor, and LiCl hygristor. The PTU data are recorded by strip chart recorder. To
        derive winds, tracking of the radiosonde is being done by a mix of radars (with attached
        target), automatic, and manual tracking radiotheodolites.
        A new Radiosonde IMD-MK IV has been planned using an electronic switch and is
        equipped with an improved aneroid sensor, rod thermistor, and carbon hygristor. All the
        existing ground equipment is being upgraded for automatic direct ingest of PTU and
        Azimuth and Elevation data by a PC. Seven old WBRT ground equipment are being
        replaced by the new automatic tracking radiotheodolites operated at 1680 MHz. Vigorous
        online and offline quality checks are planned for further improvement of data quality. One
        calibration system has been installed for individual calibration of thermistors. Carbon
        hygristors are being produced on a limited scale. Due to the requirement of low limiting
        angles of >7 degrees elevation for getting wind data of suitable quality, 1680 MHz shall
        continue to be used at seven stations along with 401 MHz for remaining stations.
       Germany
        The radiosonde network of Germany consists of 11 upper-air stations, from which 3 are
        operated by the Military Meteorological Service. One site is designated as GUAN station.
        The stations perform 2-4 ascents per day and 10 of them fly the Vaisala RS 80-30 while
        one station is using the radiosonde produced by GRAW. The winds are derived from radar
        tracking. For environmental protection purposes 12 additional stations are utilised during
        smog weather situations. 4 ASAP Containers are shipped onboard of vessels. After the
        termination of the OMEGA system, they have changed to the Vaisala RS80-15G
        The reliability of the GPS module of the RS 80 radiosonde has been poor for radiosondes
        produced before May 1999. Due to humidity problems of the reference oscillator, many
        radiosondes failed the ground check or loose wind raw data for periods greater than
        4 minutes. Due to this effect about, 1/3 of the ASAP wind data get lost. Vaisala has
        identified the problem and started to replace the faulty modules.
        The ground based upper-air network will be reorganised during the years 1999-2004. The
        future network will consist of 3 Vaisala Autosonde systems, 7 GPS radiosonde stations,
        4 wind profiler radar and AMDAR data from about 60 Lufthansa aircraft.
        Two of the three Vaisala Autosonde systems were in acceptance testing and operation will
        start in January 2000. The third system will be delivered in spring 2000. In 2001 the
        German Meteorological Service (DWD) and the Military Meteorological Service will change
        the wind finding from tracking radar to GPS. The tender for the ground equipment and the
        radiosondes will be launched in 2000.
       Australia
        Australia operates 38 radiosonde stations, from which 12 are using the RS80G GPS and
        26 the RS80 radiosonde (both Vaisala) with winds being derived from radar tracking.
        Whilst the radar tracking technique is more cost effective and presently more reliable than
        GPS for wind finding, a number of stations are not suitable for radar tracking. These
        include the remote Antarctic stations and 8 “Autosonde” stations.

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        Between 1995 and 1997, Australia performed a number of comparison trials between GPS
        and radar tracking systems. After the resolution of wind accuracy problems in the GPS
        system discovered in the early trials, it proved possible to achieve a RMS difference
        between the two systems of less than 1 ms-1. Another problem experienced in these trials
        was a lack of reliability. A number of soundings had significant periods of missing wind
        data and some radiosondes failed to produce any winds. This problem still exists albeit to a
        lesser extent. In August 1999, Australia was experiencing 7% loss of data at Autosonde
        sites and 15% loss of data at Antarctic stations. The radiosondes in Antarctica are 10-20
        months old by August because they can only be shipped during the supply voyages in the
        southern summer. It is likely that the immature radiosonde design in this early production
        stage is the cause of the higher data loss rate.
        The overall quality of radiosonde sensors has declined in recent years. Accuracy and
        reliability problems in the PTU parameters are often more common in specific batches of
        radiosondes. It is also noted that care needs to be taken to ensure that ground systems are
        set up properly and launch procedures are very important to minimise data loss.
       Russian Federation
        The Russian upper-air network consisted of 117 upper-air stations which were daily
        performing 133 launches in 1999, compared to 128 stations with 185 launches in 1998.
        This reduction was caused by serious budgetary constraints. 19 Meteorite (operated with
        MARZ radiosondes) and 98 AVK (with MRZ radiosondes) radar systems were used. At two
        stations a pilot trial with the newly developed radiosonde RF-95 was carried out using
        Vaisala probe sets.
        By the end of 1999, the first prototype of the new commercial upper-air radar MARL-A,
        applying a phased array antennae with electronic scanning beam, was intended be
        established which can be operated with both MRZ and RF-95 type radiosondes (all
        1680 MHz).
        Taking into account the great number of Meteorite and AVK radars, which had been
        operationally applied in the network for quite a long time, a comprehensive program for
        upgrading these radars was started. It included several measures, such as replacing old
        computers by Pentium-type PCs and the transceiving microwave unit by a solid-state
        module, improving the aerial system, in particular, by introducing antennae with electronic
        beam scanning, removing energy-intensive units, etc.
       Japan
        JMA operated 18 upper-air stations with each 2 complete soundings per day (00 and
        12 UTC), and at 16 stations in addition rawin observation twice a day (06 and 18 UTC). At
        all stations equipment produced by Meisei (Japan) was applied. The wind data are derived
        from a balloon tracking radar. Upper-air observation could also be made, if required, at five
        ships owned by JMA. The Meteorological Research Institute (MRI) of JMA operated one
        radiosonde system for research purposes while these observations could be reported to
        JMA for operational use (such as NWP) with TEMP MOBIL, if necessary. The systems
        operated by MRI and at ships applied GPS radiosondes.
        According to the GCOS recommendation, high altitude observation up to 5 hPa were
        started operationally in July 1999 carried out once a day at 12 UTC at Tsukuba (GUAN
        station). Furthermore, JMA operated one rocket observational station with launches of
        rocketsondes once a week up to 60 km height, as well as measurement of PT and wind at
        descent down to 20 km.
       United Kingdom
        The Met. Office(UK) operated 11 upper-air stations, 3 of which are autosonde systems from
        Vaisala. A re-evaluation of requirements is being done and it is expected that two manned
        stations plus four Autosondes will remain in the UK and four manned systems at overseas
        locations. From the network, 5 stations are operated within GUAN as GCOS stations,
        which included among others Gibraltar, St. Helena, and Falkland Islands. So far, the
        Vaisala PC CORA system was mainly applied which was about 10 years old. Tests were
        ongoing with the new generation Vaisala Digicora 3 which has been chosen as the next UK
        operational system. Dr Graw (Germany) and Sippican (USA) systems were also purchased

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            to provide GPS height measurements for radiosonde testing. It was planned that the new
            network would have a high level of automation while the GUAN stations were not intended
            to be automated especially because of the need for using larger balloons to reach the 5
            hPa level.

2.6 Y2K status
    The session briefly reviewed the status of the Y2K compliance related to the upper-air
equipment operated by NMHSs, which were represented at the Working Group meeting. The
representatives of manufacturers had also been invited to providing information relevant their
equipment. Resulting from adequate tests carried out by the experts of Services concerned it was
found that the upper-air equipment operational applied was compliant with the Y2K problem.
Manufacturers also confirmed that their equipment would cope with the Y2K needs, i.e. they
provided the users concerned with the required information and /or software for upgrading their
systems. It was hoped by the session that the staff concerned would follow these instructions
provided as well as would timely install the required software as appropriate. However, there was
no guarantee on the full compliance if users apply PCs for date evaluation or TEMP generation,
which were individually procured. In any case, it was noted with appreciation that least the main
manufacturer intended to provide through a “Help desk” at the critical period over from the
30. 12. 99 to 15. 1. 2000 an uninterrupted service.


3.1 Report of the Rapporteur on Radiosonde Compatibility Monitoring
     Mr Elms, Rapporteur on Radiosonde Compatibility Monitoring provided a report on the results
of the work carried out so far. He provided a quarterly statistics of the mean differences and
standard deviations of the differences between 100 hPa geopotential height observations (OB) and
First Guess (FG) Fields for 00 and 12 UTC for all land radiosonde stations5. These summaries,
from Q1 (January to March) 1998 to Q4 (October to December) 1999 were generated from monthly
data produced by the European Centre for Medium Range Weather Forecasts (ECMWF) in
Reading (UK).
    In comparing these data with the 3 years’ (1995 to 1997 inclusive) data displayed in the
previous Rapporteur’s report6, two notable contrasts were highlighted:-
       i)There has been an overall 30% reduction in the number of Russian Federation stations
         making observations during the last 2 years.
     ii) There is evidence of a systematic difference between the Vaisala RS80 (OB-FG) biases
         evaluated for daytime measurements at European and USA stations.
     Related to the latter, daytime data for approximately 35 RS80 stations in the USA showed an
average 3-monthly bias in the 100hPa geopotential height of about 25m lower than those in
Europe. This corresponds to RS80 mean temperatures from the surface to approximately 16km
being systematically about 0.4C colder in USA than in Europe in relation to the model field.
These systematic differences have been present in the ECMWF monitoring data since the last
quarter of 1997 and are confirmed by similar biases when the UK Met Office Model is used as the
First Guess comparison field.
   The Working Group invited the Rapporteur to further investigate the reasons for these
3.2 Quality assurance of the radiosonde observing system
    The meeting considered in depth matters related to the quality assurance of upper-air
observations. In this regard, the chairman alerted participants’ attention to the draft task list at
Document 10 as related to quality assurance issues. Discussion and agreement was reached on
who might contribute to various activities as it is finally reflected within the commonly agreed
workplan of the WG (see Appendix E).
    see Document 29
    Oakley, T - Instruments and Observing Methods Report No. 72 (WMO-TD-No. 886/1998
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    In further discussing the issue, members were invited to report on their overall experience
already obtained in this field of serious concern.
    Dr Dibbern reported that within the DWD of Germany a quality assurance concept for upper-air
observations had already successfully been set up for which the following 4 steps are applied:
         Formal checks of the software applied at the receiving station are carried out.
         The observer can interact with the system, i.e. if there is a need, he can change the
          profiles before the TEMP message will be distributed.
         With a time delay of 1 or 2 days a comparison will be carried out with neighbouring
          stations and with the numerical models.
         The last step of quality assurance especially used for research applications is to carry out
          homogeneity tests to be done for selected data sets.
     The WG noted with appreciation this approach and invited the experts nominated for further
dealing with this matter to take advantage of the experience gained by Germany when developing
relevant recommendations.
3.2.1 Quality assurance during the production
     The meeting considered the basic issue related to the quality assurance, namely the quality
assurance procedures applied to the production of radiosondes and related equipment.
Operational experience showed that the radiosondes of various manufacturers were subject to
variation in performance because of production difficulties, particularly with relative humidity and
pressure sensors, and in some cases the ASICs used with GPS windfinding systems. In some
national designs, quality problems with the radiofrequency transmitters were also critical. The
meeting decided to develop relevant proposals and recommendations in close collaboration with
manufacturers concerned.
3.2.2 Laboratory evaluations and calibrations
     Resulting from an intensive discussion on this matter, the WG underlined the high value of the
tests to be carried out by Member countries in getting information on the performance and
homogeneity of sensors resulting from operational production. It agreed that based on the review
of the results of laboratory tests already carried out nationally or under the auspices of
WMO/CIMO, recommendations for laboratory evaluations and calibrations should be developed
with the objective to improve the quality of observations. There was concern that the maintenance
of the standards relied on a very few countries and research institutes continuing to support the
necessary testing. These activities could easily die out as Members rationalise support for upper
air measurements, and it appears necessary that WMO + Members develop strategic plans to
ensure quality is sustained.
3.2.3 Training of operators
     Considering the urgent need for highly qualified staff to operate the upper-air systems properly
and to widely guarantee accurate and reliable data, the meeting discussed measures on how to
improve the knowledge and skills of experts concerned. It underlined the importance of in-situ and
of more basic training of operators which should primarily be carried out by NMHSs nationally and,
as far as possible, organised by WMO on regional levels. The Working Group agreed that a basic
programme for training events should be developed to assist Members in their efforts to organise
training. In addition, specific more detailed training material and guidelines should be prepared
which could generally be applied by lecturers for facilitating their preparation of training workshops.
The session further agreed that experts of the WG should be consulted in preparation of WMO
workshops either in supporting the selection of suitable lecturers or assists themselves in this
3.2.4 Pre-flight quality checks
     The Working Group noted the importance of applying pre-flight checks to ensure the reliability
and quality of observations. It considered the need for reviewing already existing guidelines in
adapting them to the latest requirements as caused by various factors, such as the application of
new radiosondes or radiosonde systems. This, for example, recently happened when the new
GPS-based systems were introduced into operation. An example of specific guidelines developed
for the application of Vaisala GPS radiosondes can be found attached as Appendix F. The WG

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agreed that further work has to be done in this regard and agreed on the responsibility for this task
as reflected in the Workplan (Appendix E).
3.2.5 Results from national / bilateral comparisons
     Experts were invited to report on results obtained from national or multilateral radiosonde
intercomparisons with the objective to derive conclusions on how to proceed best in this regard by
the Working Group.
    Dr Dibbern presented results obtained from a GPS radiosonde intercomparison carried out at
the Lindenberg Observatory in Germany7 at which radiosondes of 3 manufacturers have been
compared, namely:
          BBL Elektronik (Germany)
          Dr. Graw Messgeräte (Germany)
          Vaisala (Finland)
     The main objective of the comparison was to evaluate the accuracy and smoothing of wind
observations as well as the precision of the temperature and humidity measurements. The
obtained data were compared against the equipment operationally applied in the DWD, i.e. the
Vaisala RS-80 radiosonde and tracking radar from Gematronik (Germany). In noting that the
radiosonde of BBL was still under development, the main purpose of this participation was to
detect software errors. The 3 manufacturers concerned were directly involved in this test. The
results of this test are reflected in Document 15 which provides useful general information on the
performance of radiosondes involved and, in addition, detailed information on the reasons for some
deficiencies in wind, temperature, and humidity data.
     The WG discussed this matter in detail and agreed that further activities should be undertaken
for getting information on the results of nationally or bilaterally held intercomparisons. It was noted
that these tests were generally serving specific purposes determined by the national needs.
Because these comparisons were not organised according to the rules adopted by WMO/CIMO for
carrying out these tests and evaluating their results, namely by an International Organising
Committee, which has to be set up by the president of CIMO, their final results cannot be published
by WMO. However considering that the results, as reflected within the final reports, could be very
useful for experts and Services, it was proposed to make them accessible through WMO’s/CIMO’s
Web page by providing a hyperlink to the related report which has to be put on the national Web
page of the Member country concerned. The meeting agreed that Mr Elms as Rapporteur on
Radiosonde Compatibility Monitoring should undertake necessary activities for getting the related
information from NMHSs and inform WMO on it.
                                                 J. Elms collects information on national RSO tests M 2

3.3 Review of data quality, including relative humidity measurements
     The WG considered the experience generally obtained from upper-air observations, the results
of the previously carried out series of WMO radiosonde intercomparisons which included the most
recent WMO Radiosonde Humidity Sensor Intercomparison as well as of tests carried out
nationally or bilaterally. This included some detailed information provided by Dr Griersmith on
national comparisons between surface relative humidity and RS-80A Vaisala radiosonde
measurements at release. There was an apparent dry bias, but because the study is correlative,
no definitive causal conclusions were available. There was a possibility that the actual surface
observations are not totally accurate and/or representative of the radiosonde release point. In
addition to this, Mr Elms provided results of an UK comparison study of Vaisala RS-80 radiosondes
equipped with H-humicaps and VIZ radiosondes investigating the dry bias in relative humidity for
conditions when the radiosondes were observed to pass through clouds. The Chairman noted that
the raw data of both studies might be considered for further evaluations. Mr Hoerhammer informed
that Vaisala had already implemented a number of amendments for improving the humidity
measurements. He also underscored that there were quite a few sites available worldwide
attempting to understand the upper-air humidity measurements properly.

    See also Doc. 15
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     Mr Mannoji informed the session on results of a comparison between GPS precipitable water
(TPW) data and humidity data from radiosonde (see Document 27). A radiosonde station in
Thailand as part of the GAME IOP was used. TPW showed diurnal variation with a minimum at 06
UTC. Just after launch radiosondes often showed a big drop (approx. 30%) in RH. Comparison
between GPS TPW versus radiosonde TPW generally showed a dry bias. Comparison between
radiosonde and NWP model data also showed a dry bias of about 15% while no explanation was
available yet. Resulting from the discussion it was considered the possibility that the type of
radiosonde (AIR) used was not very suitable (i.e. the RH sensor positioning might not be optimal,
with significant solar heating in daylight).
    The session was also briefed on the results of a test that was undertaken by the UK
Met. Office in May 1999 for validation of the AMSU-B (Advanced Microwave Sounding Unit), a
passive sounding sensor provided by the UK Met. Office which was flown on the NOAA-15
satellite. Four radiosonde types were compared which also including an expensive chilled mirror
sensor “Snow White” produced by Meteolabor Switzerland.
     In considering the results of the previous WMO intercomparisons as well those contained in
the above reports given, it was agreed that the quality of measurements obtained from different
types of radiosondes is not yet fully satisfactory. It needs further efforts of the WG to evaluate the
quality of temperature especially of humidity measurements while especially the characteristics of
the various GPS windfinding systems needs further considerations. The WG agreed that further
tests should be carried out in this regard with the objective to derive guidelines and
recommendations for application by Members as well as manufacturers aimed towards an
improvement of the reliability of the systems, as well as the accuracy and homogeneity of the data
obtained. Measures and responsibilities in this regard are reflected within the Workplan, which is
attached as Appendix E.
3.4 Status of GPS windfinding systems
     The WG recognised that since the operation of the Omega windfinding system was ceased
late in 1998, nearly 200 GPS-based systems were operated by more than 50 Member countries
which is nearly ¼ of the upper-air stations of the GOS which reported regularly. Most of these
systems didn’t work in a fully satisfactory fashion yet, with the reliability of wind measurements
poorer than expected8. It was noted with appreciation that several improvements were already
introduced by Vaisala, which was so far the main provider of these GPS systems for NMHSs.
These improvements had led to some improvement in availability of winds in some countries, but
there were still areas with outstanding problems. Information was also given on the results of
related WMO questionnaire sent to all Members operating GPS radiosondes. WMO received 27
responses, which contained data on their operational performance obtained in the first half of
1999. It showed an overall high failure rate of up to 20% when summarising the various reasons
for not coping the needs. In underlining the usefulness of distributing queries for getting
information on the performance of GPS-based radiosonde systems, it was agreed that with support
of Mr Elms, Rapporteur on Radiosonde Compatibility Monitoring, a next similar questionnaire
should be distributed in the second half of 2000 for getting actual information on its improved
                                                                  J. Elms: Preparation of a questionnaire M3

     Participants were invited to report on the experience obtained within their Services regarding
the GPS performance. The WG noted with appreciation the results of the GPS radiosonde
intercomparison carried out in Germany as introduced by Dr Dibbern (see also Section 3.2.5
above). The main conclusion of the test done for 3 types of radiosondes was that all of them were
generally suitable for operational use regarding the upper-wind measurements while there was still
a strong need to significantly improving the humidity measurements in the upper atmosphere for
some of them.
    The WG discussed in more detail the not yet satisfactory reliability of GPS radiosondes which
also included the rejection of radiosondes when there was not lock achieved to the satellites at the
ground-check or when there was, in as it happened in some cases, a re-launch needed if the first

    See also Doc. 6
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launch failed or was aborted. It was noted in this regard that the quality requirements for GCOS /
GUAN upper-air stations of the GOS are especially high. There was a concern expressed
regarding these stations that specifically some of them may erode in performance through lack of
funding or using up supplies of radiosondes. In this connection also matters on the partly
unreliable application of GPS radiosondes within ASAP at ships were discussed9. Because most
of the GPS radiosondes operationally applied by NMHSs have so far been provided by Vaisala, the
session noted with appreciation that they had admitted the shortfalls and already implemented
several significant improvements which led to an increased reliability of the radiosondes and
especially to a better quality of wind observations.
      The session agreed in this connection that it would be useful to establish and keep up-to-date
list of Members network managers for ground-based upper-air observing systems. For getting the
information on contact persons and to establishing a database of focal point people with the
intention making it available on WMO/CIMO’s Web page, a letter should be drafted and send to
NMHSs. It is expected that this would improve communications substantially.
                                          J. Elms: Drafting a letter and collecting the information M4

     There was also a discussion on the access and use of GPS satellites especially noting some
of the problems reported at higher latitudes. Mr Curran (Sippican) informed there were a number
of Internet sites, which could indicate how many satellites could be available for use at a particular
time and location. This was useful to check whether all available satellites were being used when
GPS radiosondes were checked prior to launch or in flight. This was recognised a good diagnostic
tool to assist in determining whether there are problems with set-up or with satellite availability. Mr
Curran agreed to prepare some documentation on this matter. Since this information was already
provided prior this report was finalised, it can be found attached as Appendix G.
                                                                  T. Curran: GPS Sat. Inf. M5 (already done)

   The WG drew attention to the great value of the Catalogue of Radiosondes and Upper-air
Windfinding Systems in Use, which will regularly be updated11 and is accessible through WMO’s
Web page (URL-Address:
     In referring to Section 3.2.5 above, the WG agreed that the reliability of GPS radiosonde
systems and the quality of their measurements should be monitored further. It was confirmed that
some smaller size WMO radiosonde intercomparisons in climatic regions of most concern should
be planned. Specific attention should be directed to tropical areas first, where both the GPS
performance and the relative humidity sensor performance should be compared. The WG noted
with appreciation that Brazil was considering hosting such a test still in 2000. The WG invited its
chairman to assist the preparation of this and the following test by close collaboration with the
WMO Secretariat. Furthermore, in noting his extended experience in preparing WMO and national
tests, Dr Nash was invited to support the selection of suitable experts for serving in the
International Organizing Committee (IOC) to be set-up by the president of CIMO and to chair it.
                                                       J. Nash & WMO: IOC GPS-RSO M4 (already done)

     Finally related to this agenda item, the WG briefly discussed the process of procurement of
equipment and radiosondes. It was also noted with concern that there was an apparent lack of
options in the available commercial upper-air observing systems. The WG and WMO were aware
that individual countries’ approaches especially in procurement varied widely, and this made
collaboration in procurement difficult. It was agreed that the WMO Secretariat had a role for
information exchange without prejudice .The Internet is a good tool for this. WMO was able to use
its Web pages to assist in dissemination of information to the meteorological community. The WG

  See also Doc. 17
   It is proposed to attach it to SGs letter for reviewing the GPS sonde performance which is normally be sent
    to Services concerned only while it could simply copied to all PRs. It should be distributed in
    September 2000 for getting information from July 1999 to June 2000. It should have a similar text and
    questionnaire attached as done last year.
   The so far latest issue is dated Nov./Dec. 1999
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agreed to further develop plans and techniques for use of the WMO Web pages to assist in its
work. The plan for the establishment of an Instrument Catalogue was mentioned in this context.
3.5 Coding issues including the input of surface observations and a plan for moving from
    TEMP code to BUFR
    The meeting reviewed the present situation for coding of upper-air data by the application of
alphanumeric codes, such as FM 35 “TEMP”, and considered the need for implementation of
modern user requirements for a fuller representation of the measurements, as could be achieved
using BUFR code.
     The WG noted with concern that an immediate worldwide implementation of BUFR to best
meet the enhanced requirements of users was unfortunately not feasible. However, it was
unanimously felt that this introduction would widely solve all matters related to the various
algorithms applied for selection of significant levels which doesn’t guarantee the homogenous
transmission of data available, i.e. it causes a significant loss of quality of the data available at the
upper-air station from the sounding. It was noted that there have been problems for the
introduction of BUFR because the transition from old character codes to new binary codes is slow
and problematic. Only some 20 to 40 countries lead the way and are capable of rapidly dealing
with BUFR while the majority cannot make such changes rapidly. The issue of the code starts with
the precise definition of requirement, which then has to be transferred to the related working group
of CBS. Introduction of a new code is treated with caution, because it can be resource-intensive
activities for many Member NMHSs. However, the pressure for increasing automation in upper air
systems can be satisfied without compromising reported accuracy using BUFR code, in a way that
is impossible with TEMP code. Thus, the WG agreed to develop a proposal for a generalised
BUFR code for the upper-air observations. Dr Dibbern agreed to take the lead responsibility on
that matter.
  J. Dibbern together with volunteers: Development of a generalized BUFR for Upper-air data M5

     It was also considered that it would be excellent to already exchange internationally high-
resolution upper-air data subject to format and data volume issues. The WG noted that there were
serious consequences of the current algorithm coding procedures - either WMO should move
beyond use of the code or the current WMO selection criteria for significant levels should be
changed. It was agreed that there should a plan be established to disseminate/exchange the raw
    The WG was informed that some Members, such as UK, are already using a much tighter limit
than the WMO criteria for significant level selection for temperature (0.5K) and humidity (10%)
which guarantees a higher quality of data transmitted. It was however noted with concern that not
every Service has the ability to manually intervene and big increases in the size of the messages
as a result of changes needed to be considered in this regard too. The two matters discussed
above needed to be reconciled. The WG agreed to further consider it during its intersessional
3.6 Testing output from algorithms using standard data sets
     The global implementation and application of BUFR will take many years, as discussed in 3.5.
As alphanumeric codes will continue in use by many Members for the next decade, the WG saw a
need to continue its activity in testing the performance of the various algorithms applied for
generation of TEMP messages. The testing used standardized sets of raw data, which was already
started during the last intersessional period. The results of the previous test are reflected in
Document 14.
     The meeting briefly reviewed this report presented by Drs Ivanov and Kats containing the
results of the initial test undertaken by Russian Federation with participation of Dr. Graw
(Germany), Vaisala (Finland) and Japan Meteorological Agency. The comparison of profiles
retrieved from TEMP messages, generated by the different algorithms clearly showed that
discrepancies in retrieved profiles from original ones that were comparable to or larger the intrinsic
measurement errors of the observing systems. This leads to noticeable loss of the meteorological
information. It was agreed that Mr. Kats would submit to the WG Chairman a brief information
concerning deterioration of meteorological information after coding according to present regulation.
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The WG noted with appreciation that the final results are available in "Kurnosenko/Oakley
software"12 database format that makes them widely available for evaluation for interested experts.
     As TEMP code would remain as means for transferring upper-air data for some time it was
recognised also that it may be useful to undertake an activity aimed to achieve compatibility in
coding of TEMP messages by automated upper-air systems. It was agreed to prepare a working
plan of evaluation of “Significant levels” selection algorithms aiming to identify unacceptable errors
in algorithms, and to improve the compatibility of TEMP message output.
      The WG also invited Dr Ivanov to continue the tests with raw data sets13.
 A. Ivanov: Raw data test (preparation of a letter and collection and evaluation of results) M6

3.7 Review of automatic radiosonde launch systems
     All members of the Working Group were invited to report on the experiences obtained with the
application of automatic radiosonde launch systems. Dr Griersmith briefly described the Australian
Remote Balloon Launcher Autosonde work which involved a total of 10 stations and nearly all had
been installed and were operational. Mr Elms informed that the UKMO installed one Autosonde
station in central England which has been operationally applied for about 18 months. Operational
TEMP messages are produced about 95% of the time. Two other autosondes have just been
installed but no operational results were yet available for presentation.
     Dr Dibbern described the German deployment which would involve three autosondes. Due to
the regulations in Germany for densely populated areas, a parachute is required with the 600 g
balloon system . This complicates the auto-launching. It was reported that during early trials
snagging during launch was a problem.
     In further discussing this matter, Dr Griersmith indicated that there were several issues to note
including the need for maintenance of autosondes; manual quality control of data prior to
dissemination; recurring costs; manual refilling of the Autosonde with consumables like balloons
and radiosondes; cost of GPS radiosondes, etc.
     The Chair reiterated the value of preparing some information perhaps as a WMO IOM green
stripe report on Autosondes and some related systems. Studies on the performance of these
systems over the next 18 months were considered necessary in countries concerned like Australia,
UK, Canada, Germany, and Sweden. Also Austria and USA might be able to provide information
on other systems. It was decided to compile the available national reports on autosonde and semi-
automatic systems for the benefit of all Members. Mr Elms was invited to serve as convenor to
bring together information on these various automated and semi-automated systems. All members
of the WG are invited to provide information and reports on resources for operations, major
problems, maintenance, performance etc on autosondes and if possible of balloons applied.
       J. Elms: Coordinator for collection of “Nationally available Autosonde Information” M7
                                    (UK to provide author unless another Member volunteers.)

3.8   Recommendations from the Expert Meeting on Operational Issues for Radiosonde
      Applications in the Tropics and Sub-tropics
     The chairman introduced the report of the Expert Meeting on Operational Issues for
Radiosonde Applications in the Tropics and Sub-tropics (Geneva, 18 - 22 October 1999)14 with the
objective to review the actions and recommendations drafted as an essential basis for the
intersessional work up-to CIMO-XIII. In considering that several issues reflected within the actions
and recommendations developed by the Expert Team were already discussed and decided upon
within the previous agenda items and some others will be considered further down, it agreed on
the following remaining measures and activities from this report:
3.8.1 Matters related to the development of standardized guidelines for the procurement of
upper-air equipment for application by Member countries with a focus on accuracy, as well as on

   See IOM Report No 60 (WMO/TD-No. 771)
   It might be considered to make the raw data sets accessible through WMO/CIMO’s Web-site.
   See Document 3
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reliability and availability of radiosonde measurements (see Action 2 of Document 3 under
Section 6.2) were considered in depth. Mr Bower introduced his Document 25 relevant to this
matter. He noted specifications including the need (e.g. from NCEP, USA) for latitude, longitude,
and height to be reported at each time point for the radiosonde flight. Users required this for
example in high resolution NWP. While fundamental information on accuracy requirements are
contained in the Guide to Instruments and Methods of Observation (WMO-No. 8)15, Mr Bower
suggested that these figures needed to be reviewed according to the increased needs of users
which also includes the requirements from the Global Climate Observing System (GCOS). For
example, in reflecting the NWS approach, the recommended accuracy requirements should
include 96% performance of radiosondes with no more than 2 minutes loss of data through the
flight; temperature to 0.3K; u and v components of wind 0.1 m/s; atmospheric RH should be
measured and reported to 0.1%. The meeting noted the potential concerns of manufacturers with
such demanding specifications. The WG highly appreciated the proposals submitted by Mr Bower
as reflected in Document 25. Since such guidelines are extremely important for WMO Members
and other users, further work is needed to refine and review it for common application.
Manufacturers should definitely be invited to express their views and provide comments within this
                       C. Bower (as convenor): Revision of the guidelines for procurement M8

3.8.2 According to the proposals of the Expert Meeting (see Document 3, Section 6.1), the
Working Group considered the performance of balloons based on an evaluation provided by
Mr Bower related to results achieved by the NWS of the USA (see Document 12). It came to the
conclusion that it is advisable to invite Member countries to provide information on results gained in
this respect. It was agreed that the evaluation should be made accessible to all concerned through
WMO/CIMO’s Home page.
                          C. Bower (as convenor): Colletion of results on balloon performance M9

3.8.3 The Expert Meeting explored the possibility of radiotheodolites as an alternative to GPS
radiosondes especially as the cost of the radiosondes is one third or one half that for GPS
radiosondes (see Document 3 Section 6.1 and 6.2 Action 1), Mr Bower provided in Document 8
relevant information. According to the studies carried out by the NWS of the USA, there is a
greater chance in the tropics of having balloon flights which remain at higher elevation, but at high
latitudes low elevation flights are a common occurrence hence radiotheodolites are not a viable
option. From the Table provided in Document 8 it seems that radiotheodolites for Radio-Direction
Windfinding (RDF) were best suited to operations at latitude 20 degrees. Although this
information was still very basic and needed to be refined since a vendor claimed that with a 2m
antenna a radiotheodolite might accurately work down to 6 degrees, it could already be used as a
rough guideline for any decision process in selecting appropriate upper-air equipment. Related to
the economy of the systems it has to be noted that although the radiosondes are significantly
cheaper for radiotheodolites compared with GPS-based systems, their ground station is more
expensive than a GPS system. It was also noted that new radiotheodolite antennas are often less
than 200 kg in weight and with lower requirements for rapid scan if phased-array antennae are
        There was some further discussion on radiotheodolite systems including maintenance,
which showed that radiotheodolites were successfully applied by some countries at higher latitudes
than 20 degrees. It was however recognized that there is a danger with loss of data at low
elevation angles. Mr Bower informed in this regard that according to his experience radio direction
finding systems had shortfalls especially at mid-latitudes and near jet streams. Resulting from this
consideration, members of the WG as well as national focal persons should be invited to provide
information on national experience so that these reports can be made accessible under the WMO
Home page in a section on “Radiotheodolites - national performance studies”.
            C. Bower together with J. Elms: Collection and proposal for presentation of related
                                         information to the application of radiotheodolites M10

     An excerpt is available in Appendix D of Document 3
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3.8.4 The WG discussed the preparation of concise guidance material for application by
Members concerning the operational use of radiosondes, with specific considerations related to
GPS-based systems (see Action 3 of Document 3 under Section 6.2 as well as its Appendix E).
As a first step in providing such urgently needed information, guidelines for checking the proper
operation of the current Vaisala systems can be found in Appendix F of this report.
3.8.5 In considering the need for a standardized approach to managing upper-air observations
especially related to quality checks (see Action 4 of Document 3 under Section 6.2 as well as its
Appendix F), the importance of an approach as done by the NWS of the USA for increasing the
quality and reliability of upper-air observations was highly appreciated. It was agreed that the WG
should refine and generalise this procedures applied with the objective to publish it for the benefit
of all WMO Members.
       J. Nash as convenor: Refinement of the available procedures applied by the NWS and
     preparation of a more general proposal for publication, such as at WMO’s Web-site M11

3.8.6 In underlining the importance of well educated and trained personnel for achieving
observations of high quality, the WG discussed measures on how to supporting this best. It was
agreed that the efforts should presently specifically be directed to training of operators of GPS-
based systems (see Action 5 of Document 3 under Section 6.2). The WG approved the need to
develop training material still in 2000 with the objective to organize related workshops as soon as
possible with specific attention to Africa. It invited WMO as well as NMHSs to organize and/or
support the holding of such training workshops on regional and national levels at the earliest
convenience. In this regard, the session noted with appreciation the informal advice to
consideration the organization of related training workshops in Nairobi, Kenya (in English) and
Niamey, Niger (in French) at the earliest convenience, if feasible in the years 2000 and 2001,
respectively. A draft outline for such a workshop was developed and is attached as Appendix H.
     J. Nash as convenor supported by all WG members, especially by the representatives of
               Egypt and South Africa: Development of training material for a workshop M12

3.8.7 In considering the future significantly increased needs for high quality upper-air data
especially regarding their application for the Global Climate Observing System (GCOS) (see
Action 6 of Document 3 under Section 6.2), the Working Group agreed to review the presently
existing guidelines especially related to the highest required level (i.e. up to a pressure of 5 hPa) in
the light of users’ accuracy requirements. It is proposed to prepare recommendations on
technologies and procedures for meeting these needs (such as using GPS derived height
information, higher accuracy requirements for temperature and relative humidity observations, etc.)
(See the excerpt from Table 12A of the CIMO Guide in Appendix D). Appendix D contains a
proposal for tighter specifications for upper-air observations, which still needs to be refined. It was
proposed to consider whether in revision of the table in co-ordination with GCOS and CBS there
might be a column on what is currently feasible. It was finally agreed that in revision of the CIMO
Guide this would be desirable with explanatory information, in part for manufacturer's benefit.
                    J. Nash as convenor supported by all WG members: Development of tighter
                   specifications for upper-air observations to meet increased users’ needs M13

3.8.8 The WG discussed matters for getting reliable information on the operational performance
characteristics of GPS-based radiosondes operated in the tropics and sub-tropics (see Action 7 of
Document 3 under Section 6.2). Following the suggestion of the Expert Meeting, it confirmed
recommendations to carry out WMO Radiosonde Intercomparisons with the main objective of
gaining information on the performance and reliability of the GPS wind-finding system as well as on
the temperature and humidity observations. This undertaking should be implemented after some
GPS systems are becoming more reliable and stable in its performance, which can realistically be
expected by the end of 2000. In order to speed-up this development, the first tests should be
started as soon as possible and should be carried out in a suitable climatic region. The Working
Group considered as possible places for carrying out such tests Brazil (possibly in 2000 already),
South Africa (possibly in 2001), Kenya (possibly in 2002), and another test possibly related to RA II
China and/or India. The WMO Secretariat was invited to take action towards the organization of
these tests in close collaboration with the chairman. The proposal related to the organization of
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radiosonde intercomparisons in the tropics and sub-tropics developed by the Expert Meeting was
confirmed by the WG to be used as a guideline for carrying out these tests. It can be found in
Appendix I of this report.
                   WMO Secretariat in close collaboration with J. Nash: Development of plans of
                                    radiosonde intercomparisons and their implementation M14

3.8.9 As reflected in Action 8 of Document 3 under Section 6.2, the WG considered the need of
the development of guidelines for persistence tests of upper-air observations, which will contain
certain quality procedures for possible application by all NMHSs. It noted in this regard that these
procedures would be automated and would allow global comparisons of the reliability and quality of
upper-air observations between different regions of the same climate type. Therefore the session
agreed upon that the action proposed in Section 3.8.5 above will cover this issue sufficiently.
3.8.10 The WG considering the increased importance of accurate humidity measurements in the
atmosphere, the already significantly increased performance of some related sensors, and noted
the still substantial variation of humidity measurements as reflected in Recommendation 1 in
Section 6.3 of Document 3. It agreed that Members should be invited to carefully checking the
radiosonde humidity readings against the surface observations and to make general statistical
evaluations for getting a clear picture on the performance of sensors and procedures applied as
well as on the observations obtained. Since Australia had already described two approaches to
monitoring the quality of RH it was agreed that Messrs J. Elms and A. Sharp (Australia) will
produce a preparatory document by early 2001, which would lead later to a recommendation for
CIMO-XIII which would involve guidelines for checking performance/quality of relative humidity
observations (see also Section 3.3 above).
                J. Elms in close collaboration with A. Sharp (Australia): Develop guidelines and
                                                          information on RH measurements M15

3.8.11 Regarding Recommendation 2 of Section 6.3 of Document 3 for getting a full picture on the
equipment used at upper-air stations (META-Data), all Members should be invited to apply
Section 7 (group “31313”) of the TEMP and the associated Codes.
                           WMO Secretariat was invited to undertake in consultation with CBS the
                                                                        necessary activities M16

3.8.12 The WG unanimously agreed on the importance of the information contained in the
Catalogue of Upper-air Stations and Ground Equipment which is routinely updated in WMO
according to the received information from Members and was regularly (normally annually) be
published within the WWW Operational Newsletter. Since the information received is not always
complete does not always reflect the actual situation, it was considered necessary that Members
should continuously be urged to inform WMO on any changes in their upper-air network operation
(see Recommendation 3 of Section 6.3 of Document 3). The WMO Secretariat was invited to
undertake in consultation with CBS the necessary activities.
3.8.13 With reference to Recommendation 4 of Section 6.3 of Document 3 which asked for the
development of measures for the economic use of upper-air equipment, the WG already
considered this issue under Section 3.8.3 above.
3.8.14 Measures on Recommendation 5 of Section 6.3 of Document 3 which are related to results
of a GPS-Questionnaire and asking for the regular provision of information on GPS performance
for getting a widely actual overview on their characteristics were already considered under
Section 3.4 above.
3.9 Priorities for future radiosonde developments
     The meeting briefly reviewed the present requirements for upper-air observations with the
purpose to define future needs. The WG agreed that further to the considerations on enhanced
accuracy requirements for upper-air observations (see Section 3.8.7 above) other needs should be
reflected for the benefit of data users and to be used as guidelines for instrument developers.
Based on this, a plan might be developed to define the priorities for future radiosonde
developments, which will include besides the quality of observations also economic aspects.
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                J.Nash as convenor supported by all members of the WG: Plan for priorities for
                                                       future radiosonde developments M17

   The Rapporteurs on Wind Profilers and on GPS-derived Precipitable Water Content of the
Atmosphere provided reports on the work results achieved so far.
4.1 Report of the Rapporteur on GPS-derived Precipitable Water Content of the Atmosphere
     Mr Mannoji introduced his report as given in Document 16 containing concise information on
the total precipitable water (TPW) from GPS satellite measurements. He described the beginnings
of GPS meteorology involving delays introduced via water vapour in the atmosphere. Hydrostatic
delay is about 2m to 2.5m and is proportional to surface pressure. However wet delay changes
rapidly and varies in space and time from about a few cm to several tens of cm. Precipitable Water
Content (PWV) is modelled using an average of all GPS satellite observations above the cut-off
angle centred on a GPS receiver.
    He reported that many intercomparison studies have been undertaken. For example GPS
TPW has been compared to TPW measured via a microwave radiometer.                    Microwave
measurements are unsuitable in rain areas because liquid water makes noise in such areas.
Comparison between GPS derived TPW with radiosondes and NWP models are generally good.
One error in TPW from GPS is the tidal effect. At high values of TPW around 50 to 60mm possibly
the GPS data are slightly low compared to radiosonde data.
     Mr Mannoji’s paper describes current GPS networks around the world. In Japan the
Geographical Survey Institute operates a network of about 950 GPS receivers for seismological
purposes and this allows an excellent opportunity for meteorological operations. The average
spatial interval is about 20 - 30km. Colour maps of three hourly data over Japan show passage of
a front and associated water vapour changes toward drier air. These data are very important in
NWP models. NOAA also operates a dense network collocated with wind profilers for
experimental forecast system development.
     Mr Mannoji showed comprehensive research results including the gradient of GPS delay (a
function of temperature and moisture) which can be derived when there are many satellites
azimuthally spread around each GPS receiver site. Research suggests that dry/wet regions and
their evolution may be inferred from zenith wet delay. Sequences of radar images matched with
TPW GPS images show that prior to rainfall/cloud formation there is a marked build-up in TPW.
Hence this suggests that GPS TPW may be useful in operational rain forecasting. There were
around 40 GPS receiver stations used covering one southern Japan Island in this study. The
Forecast Systems Laboratory (FSL) in USA NWP skill scores on forecast precipitation accuracy
show improvements with GPS TPW.
     Further research on tomography is continuing as another application. Three-dimensional
structure of refractive index has also been studied. Hence some vertical structure can be inferred
from the GPS data. Down-looking GPS has also been studied - this involves the occultation
technique with a GPS receiver at the top of a mountain and signals detected from a satellite at
varying elevations and hence via signals travelling different path lengths. GPS receiver on a
balloon is also possible. This work is performed in Spain. GPS receivers on boats involving
Nottingham University and UKMO require correction for movement and position of boat.
     In conclusion the GPS TPW technique has the following characteristics:
             high accuracy
             high temporal resolution up to 5 min
             detection of likely rainfall areas before clouds have formed or precipitation has begun
             all weather operation
             low cost
             accuracy depends on accuracy of GPS satellite system
    Considering the accuracy of the determination of the TPW depends on the precise real-time
(RT) information on the orbit of the satellites concerned, Mr Mannoji informed that predicted orbits
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of 50cm accuracy are available in real-time, however 10 cm accuracy orbit data is only available in
1-2 days; while 5cm in approximately 2 weeks. For good GPS TPW accuracy 20cm accuracy in
GPS satellite orbits is needed. Scripps is working on this. Otherwise only non-real-time is
     The main networks are operated by:
               GSI Japan
               NOAA USA
               UCAR and Suomi net USA
               COST 731 Europe
               Wavefront UK
               Magic Mediterranean
    Mr Mannoji on making an excellent start on his work and providing an impressive concise
overview on this new promising field (see Document 16) was invited to review and expand this
report with the objective to publish it within the WMO/CIMO IOM green stripe series (see also
Section 2.2. above)
      N Mannoji: Preparation of a report on GPS TPW for publication (already reflected in M1)

4.2 Report of Rapporteur on Wind Profilers
     Dr Dibbern spoke to Document 13 and presented his work on wind profilers. He described the
major networks around the world. For example about 30 wind profilers (400 MHz band) within the
NOAA network provide data available in real time on GTS. He also covered issues such as GTS
data exchange and radio frequency allocation.             It was very important for network
managers/planners to contact their national authorities and local experts to ensure the viability of
their networks in terms of available frequencies.
    Dr Dibbern asked for contacts on wind profilers in other NMHSs especially non-European
whom he could liaise with to generate a global guide on profilers including siting, frequency
considerations, operations, system requirements, maintenance etc. The members of the WG from
Australia, China, India, Russian Federation, and Japan are invited to inform Dr Dibbern on the
names of contact persons from their Services.
     Within the discussion of the report provided by Mr Mannoji, Dr Ivanov (see Document 19)
informed on the Russian Federation developments in remote sensing of upper-air parameters
              wind profilers (one of the key problems encountered included difficulties in getting
               frequency allocation);
              passive radiometers;
              GPS-based water vapour or temperature measurement systems (errors he believed
               could be 1-4 K);
              acoustic radars (sodars - useful in low levels although there can be noise problems).
     Dr Dibbern was invited to prepare a publication within the WMO/CIMO IOM series on wind
profiler systems around the world. The focus would be on those systems that are in operational
phases. Mr Bhatia will support this work by arranging for a brief written report on the Indian wind
profiler work while Dr Ivanov agreed to prepare further information for supporting this work too.
           J. Dibbern with support of Messrs Bhatia and Ivanov: Preparation of a report on wind
                                                                   profilers for publication M18

    The Chair expressed the view that a special meeting would be desirable focussing on remote
sensing issues, which should be reflected within the WG work plan

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    The Rapporteurs on the Calibration of Satellite Sounding Systems and on Atmospheric
Turbidity Measurements provided their report on their work results achieved so far.
5.1 Report of the Rapporteur on the Calibration of Satellite Sounding Systems
    Dr Griersmith presented his report which was well received. The details may be found in
Document 20.
    During subsequent discussions Mr Bower commented that there were radiosonde errors of
about 2-3K in the upper stratosphere due to short wave and long wave radiation impacting on the
radiosonde. Currently climatological information was used in making corrections but he wondered
whether satellite data could be used to improve the situation. It was agreed that this topic should
be further investigated. Dr Nash indicated that parameters likely to be very useful included albedo
and height of cloud. He also recommended the use of radiosonde sensors, which were designed
to minimise the impact of the radiation notably in the stratosphere. He explained that new
generation radiosondes included a metallic coating with very low emissivity in the IR, which
reduced problems. He noted that past use of white paint (which is black in the IR) created a big
problem for getting stratospheric temperatures from radiosondes. Dr Nash also presented some
recent results of intercomparisons of various radiosondes nighttime flights. He suggested that the
RS90 radiosonde performed well at night. In general the RS90 appears to have less solar heating
problems than the RS80.
    In coming back to the satellite matters, Mr Bhatia agreed to assist Dr Griersmith in his work
while the interests of Dr Virchenkov (representing CAgM) would be accommodated with respect to
remote sensing as appropriate.
     Finally the session invited Dr Griersmith to summarise his work results prior to CIMO-XIII
within a WMO/CIMO IOM publication.
          D. Griersmith with support of Mr Bhatia: Preparation of a report on satellite issues for
                                                                                publication M19

5.2 Report of the Rapporteur on Atmospheric Turbidity Measurements16
    Over the period several global networks using modern and automatic spectral radiometers
have been established to provide aerosol optical depth parameters. Unfortunately, data from these
networks has yet to be joined into a uniform database as each of the systems use very different
protocols for data collection and processing. In collaboration with WCRP Baseline Surface
Radiation Network (BSRN) and the WMO World Optical Depth Research Centre (WORDC,
Davos), a draft specification for the measurement and reporting spectral transmission data (the
precursor to aerosol optical depth) was developed in 6th BSRN Scientific Meeting in May 2000.
     Several intercomparisons of spectral radiometers used for monitoring aerosol optical depth
were held by Members with intra-national and international participation.                While these
intercomparisons showed that the measurement of aerosol optical depth had improved over the
last decade, the development of a globally available referencing system like the World Radiometric
Reference, and data reduction algorithms were still essential for the uncertainty of aerosol optical
depth to be less than 0.015 in regions of the solar spectrum unaffected by water vapour and mixed
gases extinction. The increased use detector based irradiance standards by various Members has
improved the monitoring of radiometer stability. However, recent hyperspectral measurements of
the solar spectral irradiance at the top of the atmosphere indicate that previous confidence in the
solar spectrum maybe misplaced. Until the later is resolved, the use of spectral irradiance
standards as a step in calibrating radiometers for deriving aerosol optical depth will increase rather
than decreases the uncertainty.
    At the forthcoming Ninth International Pyrheliometer Comparison at Davos, Switzerland, to be
held in autumn 2000, the WRC is hosting a small intercomparison of spectral radiometers. It is

     Dr B. Forgan (Australia) was not able to attend the session and provided his report in a written form.
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hoped that this intercomparison will enable an initial traceability to the WORDC trap detector
transfer standard for spectral radiometers.
     Dr Nash gave an overview of radio frequency (RF) matters from his perspective as a member
of the CBS Steering Group on Radio Frequency Coordination and his very active involvement in
the field in recent times. He especially informed on the activities in preparation of the World Radio
Communication Conference (WRC-2000) to be held in Istanbul, Turkey, in June 2000. The actual
issues on radio-frequency allocations are concisely reflected in Document 11.
     He noted a number of documents prepared for the WG session which also addressed
important RF issues (such as Documents 13 and 20). It was agreed that it would be desirable for
CIMO to appoint a Rapporteur on RF compatibility issues and Mr Dave Franc of NWS (USA) might
be considered in this regard to be nominated. (Dave attended the WRC-2000. It would be better to
get this organised sooner rather than later, because there is work to do immediately).
    Dr Nash led a discussion on the two major bands of interest to sonde operators. For the
MetAids band 400.1-406 MHz it was noted that 400 to 401 was allocated in 1992 to Mobile
Satellite Services (MSS). MetSat DCPs were primary from 401-403 and in countries other than
Australia , 403 to 406 had MetAids primary. There were some strong pressures for MSS to be
given 405-406 MHz. However, most countries were probably going to vigorously oppose 405-406
being used by MSS.
    For the 1675-1710 MHz band similarly there was once again strong pressure for MSS usage
which could undermine MetAids for example from 1683-1690 MHz. Details may be found on the
WMO Web page.
    In summary the WG resolved that RF issues potentially threatened the viability of
meteorological observation systems notably sondes, satellites, profilers and the like. There were
enormous pressures in the two main bands of interest to sonde operators namely 400-406 MHz
and the general band 1675-1710 MHz. In particular mobile phone systems and ground-based high
capacity interactive communications systems were major threats.
Note: Following WRC-2000, the proposal for MSS downlink use between 405 to 406 MHz has
     been suppressed. There is a chance that the MSS will now try for downlink frequency use
     between 401 and 403 MHz. The pressure for MSS uplinks between 1683 to 1690 MHz
     continues, and further meetings to define WMO policy will be required. This proposal affects
     both MetSat and MetAids operation in the band.
     Based on the results of the discussion and the proposals agreed upon, the meeting
summarized the targets for its work within the intersessional period. It considered the general
contents of the individual reports and contributions as well as on the structure of the report of the
chairman of the Working Group to be submitted to CIMO-XIII. It was agreed that the nominated
rapporteurs will prepare and submit their individual report while information on their size will be
provided at a later stage. Furthermore consideration was given as to how to present other working
results, such as reports of intercomparisons or progress reports in specific fields which is already
reflected within the related sections of this report.
     A draft work programme for the WG was discussed in detail including future structure and
meetings. The work plan is reproduced in Appendix E while the work programme contains the
following activities:
   1.   Expert Meeting on Remote Sensing (if feasible at all due to financial constraints). It might
        preferably be held in April 2001. Considerations might be taken by the WG members
        concerned to hold it in USA or Germany, or in WMO in Geneva. The main participants are
        the following members of the WG: Mssrs Mannoji (Japan), Dibbern (Germany), Virchenkov
        (Russia), Bhatia (India), Griersmith (Australia), Nash (UK), and some other experts which
        still need further considerations.
   2.   Expert Meeting on RSO Network Management (to be organized as a joint CIMO/CBS
        activity). It is proposed to be held in December 2001 preferably in WMO Geneva.
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   3.    WMO GPS Radiosonde Comparison in Brazil (December 2000) and the meeting of the
         International Organising Committee for it (Brazil, August 2000)
   4.Training Workshop Radiosondes with special attention to the GPS-based windfinding
     system (late in 2000 or better in 20001) in Africa (possibly in Kenya)
   With regard to the structure of work to be done which is of concern of the present WG after
CIMO-XIII it was proposed to consider splitting the WG as follows:
   A. Working Group on Scientific and Technical Developments in Radiosonde Techniques and
  B. Working Group on Scientific and Technical Developments on Scientific and Technical
       Development in Remote Sensing
    It was recognized in this connection that coordination between satellite systems and ground-
based observing systems was extremely important.
    It was emphasised that the above lists represented proposal for further discussions only.
Since there would be no further specific meetings of the whole present WG – email would be used
as one means of communication for exchange of all information.
8.1 Y2K problem
     It was noted that vendors of upper-air equipment informed WMO as well as their customers
that most of their systems, with the exception of very old one, can be updated accordingly which
was manly done by software implementation. Although having this in mind, especially PC-based
systems may need much more efforts by the user concerned to check their Y2K compliance.
Information on this might be possible to be received by WMO such as see through WMO’s Home
8.2 TECO-2000 and METEOREX-2000
     A WMO Technical Conference on Meteorological and Environmental Instruments and
Methods of Observation (TECO-2000), organized under the auspices of CIMO, and an
Exhibition of Meteorological Instruments, Equipment and Services (METEOREX-2000) will
conjointly be held in Beijing, China, from 23 to 27 and 24 to 26 October 2000 respectively.
     TECO-2000 will scientifically be organized by WMO and the President of CIMO set-up an
International Programme Committee for this task while the exhibition will be prepared under the
responsibility of the China Meteorological Administration only.
The overall conference theme of TECO-2000 will be:
        Operational Measurement Technologies for the Next Decade – Critical Change or Business
        as Usual ?
The main topics to be covered within the individual sessions are:
        1.   Measurement Technology, Performance and Quality Assurance related to:
                Surface Observation Systems
                In-situ and Remote Upper-air Observing Systems
                Weather Radars and Lightning Detection Systems
                Measurement of the Atmospheric Composition
                Instruments and Systems Operated under Harsh Environmental Conditions (such as
                  extreme wind conditions, including snow or sandstorms; very high or low
                  temperatures, strong ice and snow conditions, etc.)
        2.   Management of Technical Support for Meteorological and Environmental
        3.   Capacity Building and Technology Transfer related to Instruments and Methods of

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    More information on TECO-2000 as well as on METEOREX-2000 will be made available
through WMO’s Internet Home Page (URL-Address:
8.3 Vaisala Award
      As it might be known, the “Prof. Dr Vilho Vaisala Award” will annually be awarded to the
author(s) of the best paper related to instruments and methods of observation selected by the
WMO Executive Council. These papers (max 2 per Member) have to be submitted by the PRs
concerned by 30 November prior to the year of awarding according to the guidelines established
for this award.
     Dr Nash thanked the participants for their active work and their valuable contributions
provided at the session. He highly appreciated the interest shown in the matter of concern and the
support given contributed to the success of the Expert Meeting.
     Mr Schulze thanked all experts for their lively discussions and their dedicated work. On behalf
of the participants, he thanked Dr Nash for his excellent chairmanship. He wished the participants
every success in their work and a safe trip home.
    All participants were unanimous in their gratitude especially to India Meteorological
Department for their excellent hospitality and for making arrangements to ensure the meeting was
a success.
     The session of the Working Group was closed on 10 December 1999 at 5.00 p.m.


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                                                   APPENDIX A

                                          LIST OF ATTENDANCE
 Name                            From                       Function
 Members of the Working Group
     1    J. Nash                UK                 Chairman
     2    C.A. Bower             USA
     3    A.A. Ivanov            Russian Federation
     4    R.C. Bhatia            India
     5    Yatian GUO             China
     6    A. Amer                Egypt
     7    Mr John Elms           UK                 Rapporteur on Radiosonde Compatibility
     8    J. Dibbern             Germany            Rapporteur on Wind Profilers
     9    N. Mannoji             Japan              Rapporteur on GPS Derived Precipitable Water
                                                    Content of the Atmosphere
     10 D. Griersmith            Australia          Rapporteur on the Calibration of Satellite Remote
                                                    Sensing Systems
     11 O.V. Virchenkov          Russian Federation Representative of CAgM
 Representatives of manufacturers as observers17
     12   M. Naaman              Metatron, Israel
     13   T. Curran              Sippican (VIZ) USA
     14   J.A. Parini            InterMet Systems, USA
     15   A. Kats                Federal State Unitary Enterprise KOMET, ROSHYDROMET, Russian
  16 J. Hoerhammer               Vaisala, Finland
  17 R. Pepin                    Geolink, France
  18 P. Charpentier              Geolink, France
  19 S. Bhatia                   India Meteorological Department
 Observers from IMD
  20 S.N. Srivastava
  21 D.K. Srivastava
  22 P.R. Rao
  23 S.S. Bhandari
  24 R.D. Vashistha18
  25 S.K. Kundu19
  26 A.A. Faruqui
  27 R. Madan (Mrs)
  28 K.C. Sai Krishnan
 WMO Secretariat
     29 K. Schulze               SSO, WWW Department
     30 D. Schiessl1             Director for Basic System


   Part-time participation
   CIMO Co-rapporteur on Urban Meteorology
   CIMO Co-rapporteur on Weather Radars

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                                                   APPENDIX B

                                           LIST OF ADDRESSES
                                       Members of the Working Group
Dr John Nash                                                Mr Ramesh C. Bhatia
The Meteorological Office, RS(5)                            Dy. Director General of Meteorology DDGM (UI)
Beaufort Park, Easthampstead                                Satellite Meteorology Division
WOKINGHAM                                                   India Meteorological Department
GB-Berkshire, RG40 3DN                                      Mausam Bhavan, Lodi Road
United Kingdom                                              New Delhi - 110003
Tel: (+44 1344) 85-5649                                     India
Fax: (+44 1344) 85 5897                                     Tel: (+91 11) 462 6021 (private: 581 2480)
Tlx: 849801                                                 Fax: (+91 11) 464 2249 or 469 9216 or 462 3220
E-mail:                                   Tlx: (81 31) 66494 or 66412 MDGM-IN
                                                            E-mail: or
Mr Carl A. Bower, Jr.                                       Dr Alexei A. Ivanov
NOAA, National Weather Service W/OSO14                      Central Aerological Observatory
- Observing Systems Branch -                                Pervomayskaya Street 3
1325 East West Highway                                      DOLGOPRUDNY, Moscow Region, 141700
SSMC 2, Room 4112                                           Russian Federation
SILVER SPRING, MD 20910-3283                                Tel: (+7 095) 408-7685 (or -6148)
USA                                                         Fax: (+7 095) 576 3327
Tel: (+1 301) 713 0722 (ext. 145)                           Tlx: 911577 ZOND SU
Fax: (+1 301) 713 0959                                      E-mail: or

Mr Ahmed Amer                                               Mr Yatian GUO
The Egyptian Meteorological Authority                       Chinese Academy of Meteorological Sciences
P.O. Box 11784                                              46, Baishiqiao Rd
CAIRO                                                       BEIJING, 100081
Egypt                                                       China
Tel: (+20 2) 284 6596                                       Tel: (+86 10) 6840 7276
Fax: (+20 2) 284 9857                                       Fax: (+86 10) 6217 5931
E-mail:                                      E-mail:

Mr John Elms                                                Dr Jochen Dibbern
The Meteorological Office, RS(5)                            Deutscher Wetterdienst
Beaufort Park, Easthampstead                                Frankfurter Str. 135
WOKINGHAM                                                   D-63067 OFFENBACH/Main
GB-Berkshire, RG40 3DN                                      Germany
United Kingdom                                              Tel: (+49 69) 8062-2841
Tel: (+44 1344) 85-5639                                     Fax: (+49 69) 8062 3827
Fax: (+44 1344) 85 5897                                     E-mail:
Mr Nobutaka Mannoji                                         Dr David Griersmith
Japan Meteorological Agency                                 Bureau of Meteorology
1-3-4 Otemachi                                              Satellite Activities Operations
Chiyoda-ku                                                  P.O. Box 1289K
TOKYO 100-8122                                              MELBOURNE, Vic. 3001
Japan                                                       Australia
Tel: (+81 3) 3212-8341 ext: 3320                            Tel: (+61 3) 9669 4594
Fax: (+81 3) 3211 8407                                      Fax: (+61 3) 9669 4168
E-mail:                           Tlx: AA30664

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                                                APPENDIX B, p. 2

Dr O.V. Virchenkov
Chief, Agrometeorological Remote Sensing Division
All-Russian Research Institute for Agricultural
82 Lenin Street
249020 OBNINSK, Kaluga Region
Russian Federation
Tel: (+7 084) 397 1593
Fax: (+7 084) 397 1446 and (+7 095) 255 2225
                                      Representatives of manufacturers
Mr Jan Hörhammer                                            Mr Thomas A. Curran
VAISALA OY                                                  VIZ Meteorological Systems Group
P.O. Box 26                                                 SIPPICAN, INC
Vanha Nurmijärventie 21                                     Ocean Systems Division
Vantaa                                                      525 Plymouth Rd, Suite 307
FIN-00421 Helsinki                                          Plymouth Meeting, PA 19462
Finland                                                     USA
Tel: (+358 9) 8949-1 or -450 (direct)                       Tel: (+1 610) 397-0183 (ext: 1)
Fax: (+358 9) 8949-210                                      Fax: (+1 610) 397 8647
E-mail:                           E-mail:
Mr Michael Naaman                                           Messrs Rémy Pepin & Patrick Charpentier
Metatron Ltd.                                               GEOLINK S.A.
24 Hadar Str.                                               Quartier La Chaume - Pont del'etoile
Herzlia 46290                                               F-13360 Roque vaire
Israel                                                      France
Tel: (+972 9) 956 2730 or 950 3550 (Priv)                   Tel: (+33) 4 4232 9900
    (+972) 5040 6352 (Cellular)                             Fax: (+33) 4 4232 9495
Fax: (+972 9) 956 2729                                      E-mail:
E-mail: or
Mr Joseph A. Parini                                         Mr S. Bhatia
InterMet Systems                                            India Meteorological Department
6095 28th Street SE                                         Mausam Bhavan, Lodi Road
Grand Rapids, MI 49546                                      New Delhi - 110003
USA                                                         India
Tel: (+1 616) 285 7810                                      Tel: (+91 11) 461 9657
Fax: (+1 616) 957 1280                                      Fax: (+91 11)
E-mail:                         E-mail:
Dr Alexandre Kats
Federal State Unitary Enterprise KOMET
3, Building 6, Pervomayskaya Street 3
DOLGOPRUDNY, Moscow Region, 141700
Russian Federation
Tel: (+7 095) 408-6104
Fax: (+7 095) 408 6865
Mr Klaus Schulze                                            Mr Dieter C. Schiessl
Senior Scientific Officer                                   Director for Basic Systems
World Meteorological Organization                           World Meteorological Organization
7 bis, Avenue de la Paix                                    7 bis, Avenue de la Paix
P.O. Box 2300                                               P.O. Box 2300
CH-1211 Geneva 2                                            CH-1211 Geneva 2
Switzerland                                                 Switzerland
Tel: (+41 22) 7308-409 (direct)                             Tel: (+41 22) 7308-369 (direct)
Fax: (+41 22) 7308 021 (direct)                             Fax: (+41 22) 7308 021 (direct)
E-mail:                                      E-mail:
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                                                   APPENDIX C

                                           LIST OF DOCUMENTS20

 Doc.         Item    Title                                                       Author
 Doc. 1      1.3      Provisional Agenda                                          WMO Secretariat
 Doc. 2      1.3      Explanatory Memorandum to the Provisional Agenda            WMO Secretariat
 Doc. 3      3.8      Recommendations from the Expert Meeting on                  WMO Secretariat
                      Operational Issues for Radiosonde Applications in the
                      Tropics and Sub-tropics
                      - Final Report of the Expert Meeting
 Doc. 4      3.2.3    Training of operators                                       P. Rae, South Africa
                      - Training of Operators related to Upper-air Observations
 Doc. 5      2.5      National Progress Reports - Information on the              D. Griersmith and
                      performance of the upper-air network in Australia           A. Sharp, both Australia
 Doc. 6      3.4      Status of the GPS windfinding systems                       WMO Secretariat
                      - Summary of the results of a WMO survey on the
                      performance of GPS-based radiosonde systems
 Doc. 7      2.5      National Progress Reports - Information on the              C. Bower, USA
                      performance of the upper-air network in the USA
 Doc. 8      3.8      Recommendations from the Expert Meeting on                  C. Bower, USA
                      Operational Issues for Radiosonde Applications in the
                      Tropics and Sub-tropics - Radiotheodolite Alternative to
                      GPS Radiosonde Systems in the Tropics and Subtropics
 Doc. 9      7        Preparation of Work Plans and Targets                       J. Nash, UK
                      - Draft Work Plan
 Doc. 10     7        Preparation of Work Plans and Targets                       J. Nash, UK
                      - Proposal for allocation of tasks to the members of the
                      Working Group
 Doc. 11     6        Radio-frequency Allocations for Ground-based Observing      WMO Secretariat
 Doc. 12     3.8      Recommendations from the Expert Meeting on                  C. Bower, USA
 REV                  Operational Issues for Radiosonde Applications in the
                      Tropics and Sub-tropics - Meteorological Sounding
                      Balloons and Performance
 Doc. 13     4        MATTERS RELATED TO GROUND-BASED REMOTE                      J. Dibbern, Germany
                      SENSING SYSTEMS - Report of the Rapporteur on Wind
 Doc. 14     3.6      TESTING OUTPUT FROM ALGORITHMS USING                        A. Ivanov, Russian
                      STANDARD DATA SETS                                          Federation
                      - Experience obtained in the Russian Federation -
 Doc. 15     3.2.5    RESULTS FROM NATIONAL / BILATERAL                           J. Dibbern, Germany
                      - Results of a GPS radiosonde intercomparison carried
                      out at the Lindenberg Observatory, Germany -
 Doc. 16     4        MATTERS RELATED TO GROUND-BASED REMOTE                      N. Mannoji, Japan
                      SENSING SYSTEMS
                      - Report of the Rapporteur on GPS Derived Precipitable
                      Water Content of the Atmosphere -
 Doc. 17     2.5      NATIONAL PROGRESS REPORTS - Information on the              J. Dibbern, Germany
                      performance of the upper-air network in Germany -

     Are accessible through WMO’s Web page.
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                                                APPENDIX C, p. 2

 Doc.         Item    Title                                                         Author
 Doc. 18     2.5      NATIONAL PROGRESS REPORTS - Information on the                A. Ivanov, Russian
                      performance of the upper-air network of the Russian           Federation
                      Federation -
 Doc. 19     4        MATTERS RELATED TO GROUND-BASED REMOTE                        A. Ivanov, Russian
                      SENSING SYSTEMS                                               Federation
                      - Description of the present status of the remote upper-air
                      observation performed in the Russian Federation -
 Doc. 20     5        MATTERS RELATED TO THE COMPATIBILITY OF                       D. Griersmith, Australia
                      OBSERVING SYSTEMS - Report of the Rapporteur on
                      the Calibration of Satellite Sounding Systems
 Doc. 21     6        Radio-frequency Allocations for Ground-based Observing        D. Griersmith on behalf of
                      Systems - An Australian Perspective                           J. Beard, Australia
 Doc. 22     6        Radio-frequency Allocations for Ground-based Observing        D. Griersmith, Australia
                      Systems - An overview of the use of the radio-frequency
                      spectrum by the Bureau of Meteorology -
 Doc. 23     2.5      NATIONAL PROGRESS REPORTS - Information on the                P. Ray & M.P. Pretorius,
                      performance of the upper-air network in South Africa -        South Africa
 Doc. 24     2.5      NATIONAL PROGRESS REPORTS - Information on the                Yatian Guo, China
                      performance of the upper-air network in China
 Doc. 25     3.8      Recommendations from the Expert Meeting on                    C. Bower, USA
                      Operational Issues for Radiosonde Applications in the
                      Tropics and Sub-tropics - Guidelines for procurement
                      contracts for upper-air equipment with specific attention
                      related to the accuracy and availability of radiosonde
 Doc. 26     2.5      NATIONAL PROGRESS REPORTS - Information on the                N. Mannoji, Japan
                      performance of the upper-air network in Japan

 Doc. 27     4        MATTERS RELATED TO GROUND-BASED REMOTE                        N. Mannoji, Japan
                      SENSING SYSTEMS - Diurnal variations of total
                      precipitable water (TPW) at Nong Khai, Thailand, during
                      GAME IOP
 Doc. 28     2.5      NATIONAL PROGRESS REPORTS - Information on the                R.C. Bhatia, India
                      performance of the upper-air network in India

 Doc. 29     3.1      Report of the Rapporteur on Radiosonde Compatibility          J. Elms, UK

 Doc. 30     5        MATTERS RELATED TO THE COMPATIBILITY OF                       J. Nash, UK
                      OBSERVING SYSTEMS - Quality Evaluation of AMDAR


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                                                   APPENDIX D

             Guide to Meteorological Instruments and Methods of Observation
                                                    WMO-No. 8
                                               (Sixth Edition, 1996)
                                                   Excerpt from
     Part I / Chapter 12 - Measurement of Upper-air Pressure, Temperature, and Humidity
                                                    ANNEX 12.A
       Accuracy requirements (standard error) for upper air measurements for synoptic
         meteorology, interpreted for conventional upper air and wind measurements

     Variable                     Range                                Accuracy requirement
     Pressure                     From surface to 5 hPa                ± 1 hPa
     Temperature                  From surface to 100 hPa              ± 0.5 °C
                                  100 to 5 hPa                         ± 1°C
     Relative humidity            Troposphere                          ± 5 % (RH)
     Wind direction               From surface to 100 hPa              ± 5° for speed less than 15 ms-1
                                                                       ± 2.5° at higher speeds
                                  From 100 to 5 hPa                    ± 5°
     Wind speed                   From surface to 100 hPa              ± 1 ms-1
                                  From 100 to 5 hPa                    ± 2 ms-1
     Geopotential height          From surface to 100 hPa              ± 1 % near the surface decreasing to
     of significant level                                              ± 0.5 % at 100 hPa


                                     Proposal for further consideration:
It is suggested that some considerations be given to a tighter specification of upper-air data for
GCOS application, as follows:

              Variable                    Range                                Accuracy requirement
              Pressure                       From surface to 20 hPa                         ± 0.4 hPa
                                                           20 to 10 hPa                     ± 0.2 hPa
                                                                 < 5 hPa                    ± 0.1 hPa
              Temperature                                  stratosphere                       ± 0.5 °C


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                                                            APPENDIX E


     Proposal for allocation of tasks to members of the Working Group

1.   Preparation of plans for long-term quality assurance of the radiosonde component of
     the upper-air observing system
     including plans for:-
     1.1 Quality control during the production ................................ Messrs Bower, Bhatia, and Guo
     1.2 Laboratory evaluations and calibrations .....................................Messrs Ivanov and Bower
     1.3 Pre flight quality control checks ..................................................... Messrs Bhatia and Guo
     1.4 Training of operators, including reporting checks and procedures .......................... Mr Amer
     1.5 Results from national/bilateral radiosonde comparisons ......................................... Mr Elms
2.   Preparation of recommendations on affordable improvements to radiosonde systems to
     increase the uniformity of the global network of observing systems
     2.1 for regional/national networks ..........................................................................All members
     2.2 for GCOS network ............................................................................................All members
     Recommendations need to be agreed before the end of 2002.

3.   Review plans for a Tropical radiosonde comparison and of suitable link radiosondes
     Chairman of the WG and participants at the recently held Expert Meeting on Operational
     Issues for Radiosonde Applications in the Tropics and Sub-tropics
                                   [with the objective to eventual publish the results as IOM report]
4.   Review progress with GPS radiosondes and prepare recommendations for WMO tests
     4.1 ............................................................................................................. Messrs Bower/Elms
     4.2 ....................................................................................................................... Mr Pretorious
         ........................................ (and advice from the “Expert Meeting on Operational issues …”)
                                                   [with the objective to eventual publish the results as IOM report]
     4.3 Provision of information on the access of Internet sites which indicates how many
         satellites could be available for use at a particular time and location . Mr Curran (Sippican)
                                                                                               (by the end of 2000 - already done)
5.   Prepare recommendations for standardization of output from algorithms used in
     radiosonde data processing
     Including suitable standard raw data formats for flight simulation tests ....................... Mr Ivanov
6.   Prepare recommendations on future coding of radiosonde measurements e.g. use of
     Incorporation of surface measurements into upper air message, review of code table of
     radiosonde types in use ..........................................................................................All members
     This is important and recommendations should be initiated as soon as possible, i.e. by the end
     of 2000 at latest.
7.   Review monitoring of operational relative humidity measurements
     7.1 available techniques .......................................................................................All members
     7.2 results ............................................................................................................All members
     Timetable for outputs needs to be determined by the Working Group.
8.   Review operational progress with automatic radiosonde launch systems
          UK to survey relevant members in early 2001, unless other volunteer
                                                                                     Report to be produced by end of 2001.

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                                                        APPENDIX E, p. 2
9.   Review progress with ground-based remote sensing of upper air variables
          ......................................................................................... Messrs Mannoji, Dibbern, Ivanov
          ..............................................................Mr Bower (or contribution from other USA experts)
          ..................................................................................... other WG members, as appropriate
10. Participate in radio-frequency allocation negotiations and preparation of associated
          ....................................... Messrs Nash, Dibbern, Ivanov + other members as necessary
11. Review progress with aircraft measurements and compatibility with radiosonde
          ................ Messrs Dibbern, Bower, Chairman (using other available expertise in countries)
     A concise report to monitor progress and refer to other results should be prepared for
     submission to CIMO-XIII.
12. Preparation of guidance material on the practical aspects of introducing and operating
    wind profilers
          ........................................................................................................................... Mr Dibbern
                                               [with the objective to eventual publish the results as IOM report]
     To be prepared for CIMO-XIII, and possible inclusion of abstracts in the CIMO-Guide.
13. Prepare recommendations for future work on checking calibration of satellite remote
    sensing measurements and compatibility between satellite and surface based upper air
    observations, without duplicating CBS activities. A review of ARM site activities might
    be helpful, in the long term, together with ideas about establishing other equivalent
    sites that might be based around operational observing sites.
          ....................................................................................................................... Mr Griersmith
14. Preparation of a report to the Chairman on the requirements, if any, for CIMO support in
    pursuing intercomparisons or workshops for atmospheric turbidity sensors before
    2001, also to indicate support required in future from WMO, if the current CIMO
    structure is to be modified.
          ............................................................................................................................ Mr Forgan


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                                                          APPENDIX F

                                            (Information provided by Vaisala )
1. There is a problem with certain GPS sondes in that they do not receive satellite data properly
   or do not receive at all.
2. In order to minimize these problems all the radiosondes should be tested BEFORE THEY ARE
   RELEASED to ensure that they are working already on ground level.
3. Once all the preliminary sounding procedures are done, press the “STATUS” button on MW15,
   MW11 or MW12 front panel before taking the radiosonde outside.
4. MW15 / MW11 / MW12 display will give the options GENERAL, PVT and GPS. Press the “C5”
   button under GPS.
5. The display will show e.g.
                    LOC: 14          301628.4                REM: 14           301628.4
                    010630290822142521000000                                  00000000 (*)
     This indicates how many satellites are being received by the local GPS antenna (LOC) and the
     radiosonde GPS antenna which is the remote (REM). The Local antenna shows the satellites it
     is receiving in pairs of figures, 01 06 30 29 08 etc., and can receive a maximum of 12 while the
     remote can receive a maximum of 8. The example display under REM (*) is receiving no
     satellites which is typical for indoors situation. See also that both LOC and REM numbers
     for GPS time in seconds (301628.4 in the example) are updating constantly.
     For each satellite that is received by the radiosonde, a zero (0) will change to a one (1), so that
     if six satellites are received the display will show e.g. 11101101. Note that the 0 and 1 figures
     can be in any order.
6. Take the sonde outside and have someone hold it vertically in the air while you check that
   satellites are being received on STATUS display as shown above. If you are alone you can
   hang the radiosonde e.g. on a suitable pole. Remember to keep the radiosonde at least 20m
   away from the local GPS antenna. For a zero wind test the sonde must be in an open area
   where a view to the sky is not obscured. If the place is largely obstructed, zero wind test may
   not be possible (1).
7. Check the displayed wind data by pressing Data key and the C4 button for wind.              In an
      unobstructed place there should be at least 4 satellites in track enabling zero wind check on
      the ground. Notice that it takes approximately four minutes before zero wind data is available.
      The wind speed shown on the display should either be zero or very close to it. If the zero
      wind test is not possible check the STATUS display as instructed above and be sure there are
      a few satellites in track and that the satellite track display e.g. 10110000 is not oscillating
      rapidly between 0 - 1.
8. If there are no satellites in track (display 00000000) or 0 and 1 are oscillating rapidly, do not
   use this radiosonde for soundings. Keep this sonde together with its calibration tape and
   include a note describing the fault prior to returning these radiosondes to Vaisala Oyj.
9. If in an unobstructed place the zero wind check up has failed, do not use this radiosonde for
   soundings. Keep this sonde together with its calibration tape and include a note describing the
   fault prior to returning these radiosondes to Vaisala Oyj.
      (1) In places where there are known constant frequencies disturbing the GPS, a special SYSGEN setting is in use. In these places
          (like Hong Kong, Italy) zero wind testing is not possible.



     Updated on 10 December 1999

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                                                   APPENDIX G

                              Information provided by T. Curran, Sippican, USA
       The use of the Global Positioning System (GPS) satellite network for radiosonde
observations is a fairly recent development and, as such, many users are not fully aware of the
available resources for predicting GPS satellite coverage at a given location. During the initial
installation of a GPS upper-air station, the operator needs to verify that the ground GPS reception
equipment and the GPS radiosondes are able to receive the signals for all of the visible GPS
satellites at that specific location, date, and time. This type of information is also valuable for
maintenance purposes, particularly when a site is experiencing poor GPS satellite reception.
       There are a variety of websites on the Internet which can provide highly accurate GPS
satellite coverage prediction information for any location around the world. In general, these
websites require the user only to provide the following information to determine which satellites
should be visible at their location:
     Date
     UTC Time
     Latitude
     Longitude
     Altitude
     Elevation Mask *
           * The Elevation Mask is a function of the ground station GPS receiving antenna and the
              radiosonde. The user can obtain this information from the ground station/radiosonde supplier.

     An example of a website which can provide this useful information to GPS radiosonde users
can be found at the URL-Address:
      As mentioned previously, this information is available from a variety of on-line resources.
Attached is a GPS satellite coverage prediction for the WMO upper-air station in Payerne,
                                     GPS Satellite Prediction Results
                            Navigation & Datalink Section (Code 471120D)
                     Naval Air Warfare Center -- Weapons Division, China Lake, CA
Prediction for:
March 18, 2000 12:00:00 UTC (GPS week = 29 GPS TOW = 561600 seconds)
    Altitude    =        491.0 m
    Latitude    = 46° 49' 0.00"N
    Longitude = 6° 57' 0.00"E
    Using an elevation mask of 10° there are 6 satellites in view:
                     Satellite                   Elevation         Azimuth
                         GPS BIIA-24 (PRN 06)                    54.9°          62.3°
                         GPS BIIA-26 (PRN 10)                    16.0°          54.0°
                         GPS BII-05 (PRN 17)                     56.5°         153.1°
                         GPS BIIA-18 (PRN 22)                    34.3°         301.4°
                         GPS BIIA-12 (PRN 25)                    44.6°         230.0°
                         GPS BIIA-27 (PRN 30)                    33.6°         122.3°

The best GDOP is obtained using satellites: 6, 10, 22 and 30.
    GDOP = 3.8
    PDOP = 3.3
    TDOP = 1.9
    HDOP = 1.7
    VDOP = 2.8

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                                                APPENDIX G, p. 2

                                           Abbreviations used
GDOP = Geometric Dilution of Precision
       This is a measure of the quality of a satellite constellation geometry. GDOP represents
       the influence of satellite geometry on the accuracy of the user position and time
       estimates. The best geometry is that which produces the lowest GDOP value. GDOP
       acts as a multiplier of the error in position and time estimates due to other sources.
PDOP = Position Dilution of Precision
       This is a component of GDOP which reflects the effects of geometry on three
       dimensional position estimates. Again, the best geometry is that which produces the
       lowest PDOP value.
TDOP = Time Dilution of Precision
       This is another component of GDOP which reflects the effects of geometry on time
       estimates. Again, the best geometry is that which produces the lowest TDOP value.
HDOP = Horizontal Dilution of Precision
       This is a component of PDOP which reflects the effects of geometry on two-dimensional
       horizontal position estimates. Again, the best geometry is that which produces the
       lowest HDOP value.
VDOP = Vertical Dilution of Precision
       This is another component of PDOP which reflects the effects of geometry on vertical
       (altitude) position estimates. Again, the best geometry is that which produces the lowest
       VDOP value. These are common methods used to describe the various possible errors
       in GPS navigation. It is not likely a GPS radiosonde operator could use this information
       for either troubleshooting purposes or to enhance their GPS operations.


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                                                   APPENDIX H

1. Basic introduction to Radiosonde Soundings
        i)       Purpose, use and importance of upper-air data
        ii)      SYNOP TEMP messages
        iii)     Importance of CLIMAT TEMP messages
2. Handling and storage procedures for radiosondes and balloons.
3. Performing ground checks for radiosonde
        i)       Procedure for checking and calibrating PTU
        ii)      Checking of GPS reception (“zero wind” check)
4. Surface Observations for Sounding
        i)       The need for accuracy.
        ii)      Proper timing of surface and radiosonde readings.
        iii)     Location of observation site relative to release site
5. Correct procedures regarding balloons
        i)       Inflation and handling
        ii)      Attaching the sonde to the balloon
        iii)     Releasing the balloon
6. Avoidance of outside interference
        i)       From Radars
        ii)      From other radio-frequency sources
7. Keeping of detailed records regarding sonde performance


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                                                    APPENDIX I


1.   Because of the variety of humidity conditions that exists in Tropical and Sub-tropical regions, it
     becomes necessary that a minimum of three locations (more are desirable) be chosen that
     allows dry and rainy season data to be obtained.
2.   It is known that temperature measurements require corrections, therefore, the environmental
     background where the measurements are made is important and particularly influences the
     long-wave error of thermistors. For this reason it is recommended that a variety of surface
     textures be considered, i.e. tropical desert, rain forest, rain forest in dry season and rainy
     season, that allows maximum information to be obtained.
3.   Balloons able to reach 5 hPa should be used in order to extrapolate results of the
     intercomparison to those balloon/radiosonde stations that do not reach 5 hPa.
4.   Operational radiosondes from participating Members should be chosen without regard to
     special instrument selection.
5.   Intercomparison measurements should be interchanged between the participants on a daily
     basis during the test.
6.   Results of the radiosonde intercomparison should be disseminated to all Members as soon as
     possible after the intercomparison, but not later than 18 months.


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