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					Windfinding methods in the
Sounding System of Vaisala
          2000-09-27…29
           ASAP Panel
           Reading, UK

          Erkki Järvinen
       Product Line Manager
         Upper Air Division
                       Contents
• GPS Performance Improvement Project
• ASAP Automation
   • DigiCORA III
   • Automation in Sounding Processor & Launching System
   • Service & Maintenance Concept
• GPS Windfinding
• Loran-C Windfinding
   • Automatic Loran-C Chain Selection
   • On the Windfinding Accuracy of Loran-C
   • Upgrade Path from Loran-C to GPS
• RS90
    GPS Performance Improvement Project
Starting Point:

   • Vaisala’s storage tests for GPS-121 modules indicated
     in Summer 1999 an IF drift
   • Station monitoring focused to GPS performance
   • Customer Feedback analysis from windfinding
     perspective starts



   • Improvement project launched on September 3th 1999.
       • Quality manager as team leader, 10 to 15 team members
       • Project meetings twice a week
      A set of simultaneous tests started
•   Gather statistics of IF drift, magnitude of the problem
•   Aging tests
•   Aging tests in different humidities
•   Drying tests with heat treatment
•   Drying tests with heat treatment and power supply
•   Shock and g-force tests
•   Battery performance teats
•   Balloon pendulum effects
•   Oscillator clock start-up tests
•   Several test setups with electronics changes
•   Massive test sounding operation (300 soundings)
•   Engagement of suppliers in investigation (TQ)
           Conclusions / Implementation
                                                         Production Process
             Pre Aging of Crystal                        environmental
             Optimal pre-aging                           conditions (U,T)
             of module before                            - Change of prod. plant
             tuning (24h- >120h)                         implemented since
             implemented since                           week 3/00
             week 52/99
                                    GPS 121 module
                                    long term              1
                                    frequency drift                            Stabile
                                                                              121 GPS
                  GPS 121 module                                                Data
                  short term                                                 Availability
                  frequency alteration 2

Outside interference                       G-Forces
Transmitter                                -Phase lock (Doppler) characteristics
interference to                            -optimization of Ground equipment
oscillator PCB                             SW for Raw Data Utilization (test)
Stability with
                                 Stabilization of power supply
Filtering
                                 with add. filter
                         Relative humidity at sub-contractor

                    70


                    60


                    50
Relative humidity




                    40


                    30


                    20


                    10


                     0
                    98-01-05   98-02-24   98-04-15   98-06-04   98-07-24   98-09-12   98-11-01   98-12-21   99-02-09   99-03-31
                                                                                                Improvements in GPS

      Chronological order of GPS Improvements
                                                                                                                      Possible
                                                               Wider                                                    Soft
                                                                                                      GPS
Omega face out,        Radiosonde                             GPS/IF              GPS,                                 Ware
                                           Two Phase                                               Production
   GPS into             Battery                              bandwidth           Crystal                                 Up
                                           Unwinder                                                 Humidity
operational use         135 min                                v.8302           pre - aging                            Grade
                                                                                                     control
                                                               v.8303                                                scheduled




06 07 08 09 10 11 12 01 02 03 04 05 06 07 08 09 10 11 12 01 02 03 04 05 06 07 08 09 10 11 12 01 02 03 04 05 06 07 08 09 10 11 12 01
97                97 98                98             98 99                99             99 00                00             00 01




                                                                                      Improved
    WAAS Signal           Improved                New             Improved                               RF rejection
                                                                                      RS - Power
    rejection SW         GPS Receiver          operating         GPS Receiver                           improvement
                                                                                        Supply
       v. 8222             GPS 121            instructions       (electronics)                           (electronics)
                                                                                     (electronics)
Further monitoring of performance stability
 • Storage tests according to normal routine
 • Aging tests with new modules, special attention to
   crystal performance
 • Monitoring of test soundings at Vaisala
 • Monitoring of synoptical sounding network
 • Customer feedback process
   DigiCORA III




The New Generation
 Sounding System
                           DigiCORA III
The "Operator-free and LAN-based
      Upper Air system concept"
 • Standard functionality of                                a
   sounding ground station
 • PTU and Wind data collection,
   processing and archiving
 • Raw PTU data graphical display
 • All functions accessible from a single interface
 • Access to software functionality dependent on user level
    • Standard Level / Operators: Soundings only (default), expandable
    • Advanced Level / System Administrators: Soundings, simulations,
      system parameters, Operator access
 • All user prompts can be translated / localized
 • Stable and robust software design
    • Modular structure, discrete and autonomous processes
                DigiCORA III Structure
  RS90 / RS80             GPS Antenna                    Local Navaid
  radiosonde                            UHF Telemetry
                          GA20                           Antenna CA21
                                        Antenna RB21




        Radiotheodolite
        RT20A
                                                             SPS220




Sounding                                        ARCNET
Workstation
running
DigiCORA III
software
                 DigiCORA III in ASAP

Easy to use compared to existing ASAP installation:
   • Automatic Loran-C chain selection
   • Possibility to use Inmarsat C
      • Inmarsat C coordinates are fed to the system automatically
      • Compared to DCP, does not loose data in compression
      • Compared to DCP, the data transmission is 100% vs. 80%
   • Supports BUFR message format
   • In next SW-release: Possibility to feed the surface
     pressure automatically, P-value from radiosonde or from
     AWS.
                System Upgrade Path
Most surface equipment can be upgraded to DigiCORA III
      • Processor card upgrades may be required
         • PTU upgrade: PTU Processor card UPP210A
         • GPS wind upgrade: GPS Processor card MWG203
         • Loran-C wind upgrade: VLF-Navaid Processor card MWV201
      • DigiCORA MW11 / MW11A
         • MW11: Subrack upgrade to MWF12F
         • MW11A: No internal modifications required
      • MARWIN MW12 / MW12A
         • MW12: Subrack upgrade to MWF12F
         • MW12A: No internal modifications required
      • DigiCORA II MW15
         • No internal modifications required
      • Radiotheodolite RT20
         • RTC20, RTH21 and Card frame need to be upgraded
     Service and maintenance Agreement
New service concept
   • Levels of support optimized for different customer needs
   • Annual fee covers all work done within the contract
     framework
   • Simplifies maintenance
   • Guarantees up-to-date software at all times
   • Possibility of remote software updates and system
     maintenance
          Service and Maintenance Contract
CASE: DigiCORA III
Level 1: Software Maintenance (default)
      • Sounding Software updates and new versions
      • Remote Diagnostics service
      • Require efficient data transmission, for eg. Inmarsat MiniM
Level 2: 24h HelpDesk Services including Spare Parts
      •   Includes Level 1
      •   24 hour Technical Assistance service, 7 days per week
      •   Guaranteed Spare Part Availability
      •   Level 3: On-site Support
      •   Includes Level 1 and 2
      •   Annual one day site visit for Maintenance
      •   Guaranteed response times for On-site Technical
          Assistance and Expert Services
Windfinding Technology with GPS
        GPS (Global Positioning System)

24 satellites in 6 orbital planes with a 55
degrees inclination at a distance of 21000 km
from earth.

All satellites use two carrier frequencies of
1.226 (L2) and 1.575 (L1) GHz to transmit
BPSK modulated spread spectrum signals.

Signal level -130 dBm at receiver i.e. 20 dB
below thermal background noise.
                                                1575.42 MHz

Vaisala GPS: Codeless technique with
Carrier Doppler shift observable.
                                                  2 MHz
                           Doppler Observable
The GPS121 receiver in the radiosonde measures doppler
shifted carrier wave frequencies of the GPS satellites.

The doppler shift of the received signal is directly
proportional to the line-of-sight velocity between the user
and the satellite.

   f  (vline of  sight / c) f carrier

  where c is speed of light and
   fcarrier is the nominal GPS L1           Observer
  carrier frequency
                                                              Satellite
                                                       vlos
            Codeless, Digital GPS Solution

Codeless GPS receiver:
   • Zero-IF GPS radio
   • Full custom ASIC

Features:
   • Unique digital codeless 8-channel GPS receiver.
   • Digital squaring of GPS BPSK signal for spread spectrum
     removal.
   • 8 independent 4th order digital PLL’s for Doppler tracking.
   • Doppler measurement resolution 5 mHz at 24 bits
                                          GPS Windfinding

The Wind Equation

                                                                         Satellite
                                                              Sonde
                                                                         Orbit
                                                              Dopplers
        D            x          f                                      Parameters

                                                                         Local         ASHTECH
 direction sonde                sonde            Calculated              Dopplers
 cosines velocity               doppler          Wind           GPSW
                                                                         Station Position
                                                                         and Velocity

                D                v         f
d 1
   x    d   1
            y       d 1
                      z     1  v x   f 1 
                                      
d
   2
        d   2
                    d 2
                            1  v y   f 2 
   x        y         z          
 ...   ...         ...    ... vz   ... 
 n       n                      

d x    dy          d zn      
                            1   vt   f n 
            n4                 4 1      n 1
                                  DIRECTIONS, VAISALA OY (60.28 24.88), 9 transmitters
                      2000
  SOUTH - NORTH [km]




                      1500                    9007-1

                                                                                              Loran-C
SOUTH - NORTH [km]




                      1000                                9007-2

                                        9007-M
                           500
        South-North [km]




                                                 9007-3
                                                                       8000-1
                             0                                     VAISALA OY


                           -500
                                                                                                                                          HDOP = 1
                                                                                    8000-4
                                                                                                                        HDOP, VAISALA OY (60.28 24.88), sonde at 0-35 km height, 9 transmitters
                                                               8000-2   8000-M
                    -1000


                    -1500
                                                                         8000-3                                   0.8
                                                                                                                                                               VAISALA OY, HDOP = 1
                    -2000
                                                                                                                  0.6
                        -2000 -1500 -1000           -500    0     500    1000     1500 2000




                                                                                                    HDOP
                                                      West-East [km]




                                                                                                           HDOP
                                                                                                                  0.4
                                       WEST - EAST [km]
                                                                                                                  0.2


                                                                                                                    0
                                                                                                                  100
                                                                                                                            50                                                                    100
                                                                                                                                     0                                                50
                                                                                                                                                                            0
                                                                                                                                          -50
                                                                                                                                                                  -50
                                                                                                                    North-South [km]             -100   -100
                                                                                                                                                                        West-East [km]
                     Foreword
• There has been growing uncertainty in the
  meteorological community about the future of upper air
  soundings using Loran-C radionavigation system.
• This presentation summarizes latest information in
  order to give a concise view of the usefulness of Loran-
  C on meteorology.
Why Loran-C windfinding

 Advantages
    • Low cost radiosonde
    • Accurate
       • Loran-C accuracy exceeds numerical
         forecast requirements
 Limitations
    • Regional coverage
    • Sounding geometry must be taken into
      account: Automatic chain selection.
    • Chayka off-air four days each month
                              Loran-C and Chayka Coverage

                                                                             6   6 6 6 8 8 8 5 5    5    5   4   4   4   3   3   3   3 3 3 3 3 3 3     3
 80                                                                      3   5   8 1010 9 9 8 8 8   8    8   7   7   7   5   5   4   4 4 4 3 3 3 3     3 3
          5   5   5   4   3 4 3 3                                        5   5   8 8 8 9 9 9 10 8   8    7   7   7   5   5   4   4   4 3 3 3                       4
          5   5   5   6   6 6 6 7 5 4                                5   7   7   8 8 8 1212131110   9    6   4   5   5   4   4   4   3       3 5   4   4   6   5   7
 60       7   7   6   6   9 9 8 7 7 8 7 5 4 3 5 5     3    3   3 7 7 9   7   8   9 9 1211131211 9   7    6   3               3   3         4 3 5 6 6   8   7   6   7
          6   7   6   9   9 11 9 101111 9 8 7 6 9 6   6    6   5 6 5 7   6   7   7 7 101511 6 6 6   6    4                                 4 7 7 7 7   7   7   7   7
          6   4   4   5   8 8 10 9 12121310111010 9   7    7   5 3   7   4   5   6 8 8 10 8 7 6 4   3                                   3 1011131313   8   6   6   5
 40                          7 7 111011131212111011   9    7   5 3                  6 6 6 4 8 8 7   4                            5   8 121515141413    9   7
          3 3 3                3 6 7 9 9 1110 9 9 9   7    7                            4 3 7 7 5   5                            6   7 111516171413    7   5
          3 3 3                     5 5 6 7 8 6 7 6                                         4 5 5   5    3                       4   6 7 14161613 7    6   5
 20       3 3 3                           4 5 5 3                                           4 5 5   4    4                       4   5 6 9 1211 6 6    5   3
                                                                                                3   3    3                           4 4 7 7     4 3   3
      0                                                                                                                                 4


-20


-40


-60


-80

                  -150               -100                  -50                     0                50                           100             150
                                                          Station Availability, accuracy -1+2 stations

                                                NOTICE: This is an estimate of the expected coverage
Automatic Loran-C
 Chain Selection
                                                                     Good Loran-C geometry

                                                                                                                                                     HDOP = 1
                                            DIRECTIONS, VAISALA OY (60.28 24.88), 9 transmitters                     HDOP, VAISALA OY (60.28 24.88), sonde at 0-35 km height, 9 transmitters
                                    2000


                                    1500                9007-1
 SOUTH - NORTH [km]




                                                                                                               0.8
SOUTH - NORTH [km]




                                    1000                            9007-2                                                                                   VAISALA OY, HDOP = 1

                                                  9007-M                                                       0.6




                                                                                                        HDOP
                                     500
                 South-North [km]




                                                           9007-3




                                                                                                        HDOP
                                                                                 8000-1                        0.4
                                       0                                     VAISALA OY

                                                                                                               0.2
                                     -500                                                     8000-4
                                                                         8000-2   8000-M
                                    -1000                                                                        0
                                                                                                               100
                                                                                                                         50                                                                    100
                                    -1500
                                                                                   8000-3                                         0                                                50
                                                                                                                                                                         0
                                                                                                                                       -50
                                    -2000                                                                                                                       -50
                                        -2000 -1500 -1000     -500    0     500    1000     1500 2000            North-South [km]             -100    -100
                                                                                                                                                                      West-East [km]
                                                                West-East [km]

                                                            WEST - EAST [km]
                                                                     Poor Loran-C geometry

                                                                                                                                               HDOP = 11
                                            DIRECTIONS, CARDINGTON (52.10 -0.42), 3 transmitters                  HDOP, CARDINGTON (52.10 -0.42), sonde at 0-35 km height, 3 transmitters



                                                                 9007-M
SOUTH - NORTH [km]




                                    1000                                                                     50

                                                                                                             40
                                     500




                                                                                                   HDOP
                 South-North [km]




                                                                                                             30




                                                                                                      HDOP
                                       0                                  CARDINGTON                         20

                                                                      6731-M                                 10
                                     -500                                                                                                                CARDINGTON, HDOP = 11
                                                                                                            0
                                                                                                          100
                                                                      6731-X
                                    -1000                                                                             50                                                                    100
                                                                                                                               0                                                50
                                                                                                                                                                      0
                                                                                                                                    -50
                                                                                                                                                            -50
                                                 -1000    -500      0        500     1000                     North-South [km]             -100   -100
                                                                                                                                                                  West-East [km]
                                                              West-East [km]

                                                          WEST - EAST [km]
             Sounding geometry
Dilution of Precision (DOP) describes the effect of
transmitter geometry on the windfinding accuracy

Horizontal DOP       Geometry      Accuracy
   • HDOP < 5        Good          Best accuracy
   • 5 - 10          Moderate      Reduced accuracy
   • 10 - 20         Poor          Missing winds
   • HDOP > 20       Bad           No wind
      Automatic Loran-C Chain Selection

Loran-C windfinding
  • Vaisala Loran-C receiver uses two Loran-C
    chains in soundings.

Automatic Chain Selection

  • Automatic Loran-C Chain Selection selects
    the best two chains out of four predefined
    alternatives to be used in the sounding before
    the sounding starts.
  • The selection is based on station geometry
    and signal quality
           Objectives

• To get the best possible sounding geometry
  for each launch.

• To increase reliability of soundings.
   • Disturbances in signal quality (distant chains).
   • Unpredictable maintenance breaks.


• To simplify operator’s work.
        How the best chains are selected

• The predefined Loran-C chains are paired and the pairs
  are compared using quality estimates calculated for
  each pair.

• Quality estimate is based on geometry and number of
  available transmitters of a chain pair.
   • HDOP - Horizontal Dilution Of Precision describes the
     geometry.

• The smaller the value of quality estimate the more
  suitable the chain pair is for sounding purposes.
On the Windfinding Accuracy
             of
   RS90-AL vs. RS80-15L
          Loran-C
Test report 1999-02-01 ... -02-26

 24 soundings
    • 23 GPS reference soundings
    • 22 GPS vs. Loran-C soundings

 Equipment
    • MW15 + MWV201 (RS90-AL)
    • MW15 + MWV201 (RS80-15L)
    • MW15 + MWG201 (RS80-15G)
          Wind component error
Average of error estimates
System                       North   East
RS80-15G GPS                 0.04    0.04
RS90-AL Loran-C              1.10    1.13
RS80-15L (18L) Loran-C       1.21    1.32


Median of error estimates
System                       North   East
RS80-15G GPS                 0.03    0.03
RS90-AL Loran-C              1.07    1.03
RS80-15L (18L) Loran-C       1.18    1.18
                Conclusions
RS90-AL Loran-C accuracy was typically 0.1 - 0.2 m/s
better than RS80-15L (18L) accuracy in this test
series.

The RS90-AL Loran-C performance is probably
slightly better than the RS80-15L (18L) performance.

Vaisala RS80 GPS wind is a very accurate reference
for comparison tests.
        On the
Windfinding Accuracy of
Loran-C, GPS and Radar
 Juhana Jaatinen, Vaisala Oyj, Finland
John B. Elms, The Met. Office (RS5), U.K.
        Average of wind component error



Windfinding method           North [m/s] East [m/s]

GPS          MW15 (MWG201)   0.09        0.09

Loran-C      MW15 (MWV201)   0.80        1.20

Loran-C      MW15 (MWL11)    1.00        1.28

Radar        Cossor          0.76        0.63
                       Summary

Windfinding accuracy
  • GPS     Vaisala RS80 GPS is a very accurate
            reference with error less than 0.3 m/s
  • Loran-C Both Loran-C systems provide about
            1 m/s accuracy which degrades at
            ranges exceeding 150 km

  • Radar   Accuracy depends on the range.
            At short range (<60 km) more accurate
            and at long range (>130 km) less
            accurate than Loran-C.
  Upgrade Path from Loran-C to GPS


          All that is needed
for the existing DigiCORA III Loran-C
           sounding system
                 is the
       GPS-processor MWG2xx
           and SW-Upgrade
   RS90 -
high performance
radiosonde family
                    Main Features


• Improved measurement performance
      • new unique sensors, specifically designed and optimized
        for upper air measurements

• Outstanding observation data quality

• Lightweight, economical and easy to use

• Environmentally friendly design
      • No styrofoam used in the housing
    Improved Measurement Performance
• Fast temperature sensor, F- THERMOCAP®
   • Accurate temperature sensor with fast response time and minimized
     solar radiation error

• Shock-resistant pressure sensor BAROCAP®
   • Silicon pressure sensor, shock resistant, and offers a fast
     temperature response

• Fast, defrosting humidity sensor heated HUMICAP®

   • Short response time, reduces condensation and icing

• Factory calibration covers a wide measurement range and
  includes also measurement electronics
             RS90 Models Available
Model     Transmitter               Sensors   Wind finding
RS90-A    400 MHz ± 120 kHz (90%)   PTU       -
RS90-AL   400 MHz ± 120 kHz (90%)   PTU       Loran-C
RS90-AG   400 MHz ± 120 kHz (90%)   PTU       GPS

				
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