GPS Occultation

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GPS Occultation Powered By Docstoc
					New Satellite Capabilities and
Existing Opportunities
              Bill Kuo1 and Chris Velden2
       1   National Center for Atmospheric Research
                  2 University of Wisconsin
GPS Occultation
          Basic measurement principle:

          Deduce atmospheric properties based on
          precise measurement of phase delay and amplitude.
                Radiosonde Stations and Manufacturers




 Vaisala/Australia
  IM-MK3/India
   Shang/China
  MEISEI/Japan
Mars/MRZ       VIZ
        AIR
      Others




                         From Junhong Wang
Quantifying Regional Differences
     Calculate the mean absolute difference in refractivity between
      CHAMP and Radiosondes (NCR) between 5 ~ 25 km.

     Calculate the corresponding mean of the absolute value of the
      difference in refractivity between CHAMP and the ECMWF (NCE)

     Perform calculation using radiosonde data from different regions of
      the world from June 2001 to March 2004.




          From D.Rossiter (UCAR Summer Student)
Statistics of CHAMP - Radiosonde Comparison


                             Average # of
     Region     Sonde Type
                               matches

     India       IM-MK3           87        0.82/3.2   0.15/1.0


     Russia       Mars          1003        0.30/1.3   0.09/0.9


     Japan        MEISEI         107        0.26/1.7   0.14/1.1


     China      Shanghai         402        0.19/1.4   0.15/1.0


    Australia    Vaisala         366        0.18/1.3   0.13/0.9

 Fractional Refractivity Differences between 5 ~ 25 km
CHAMP - radiosonde comparison




    India                Australia
CHAMP - ECMWF Comparison




   India              Australia
COSMIC (Constellation Observing System for
Meteorology, Ionosphere and Climate)
 6 Satellites launched in early 2006
 Three instruments:
  GPS receiver, TIP, Tri-band beacon
 Weather + Space Weather data
 Global observations of:
  Pressure, Temperature, Humidity
  Refractivity
  Ionospheric Electron Density
  Ionospheric Scintillation
 Demonstrate quasi-operational GPS limb sounding with global
  coverage in near-real time
 Climate Monitoring
COSMIC sounding distribution in a day
     COSMIC Data Analysis
   New GPS “Open Loop” (OL)
    tracking firmware was implemented
    and tested on SAC-C satellite
   Initial OL results indicate:
    – Setting and Rising occultations are
      working
    – No more instrumental bias in the lower
      troposphere
    – >50% of soundings penetrate into lowest
      km
   Additional improvements are           First GPS rising occultation
    possible and currently discussed with that was inverted at UCAR,
    JPL                                   with raw data provided by JPL
COSMIC GPS RO Soundings in 24 h over the Pacific
A Short Summary
   COSMIC will be launched in early 2006, and will produce ~2,500
    GPS RO soundings per day, uniformly distributed around the
    globe. COSMIC is expected to last for 5 years (2006 ~ 2011).
   New signal tracking algorithm (open-loop tracking) has shown real
    promises for much improved soundings in the lower troposphere
    (remove negative bias, deep penetration).
   GPS RO soundings have very high accuracy and very high vertical
    resolution (great for detecting upper level disturbances).
   Loci of GPS RO soundings can be predicted two weeks in advance
    (very useful for experiment planning).
   Many more missions are being planed beyond COSMIC. GPS RO
    technique is here to stay (so we better learn how to use the data
    effectively).
 GPS radio occultation missions
Mission              Launch-Duration       # Soundings/day   Remarks
GPS-MET              4/1995     2+               ~125        Proof of Concept

CHAMP                11/2000    ~5               ~250        Improved receiver, tracking

SAC-C                11/2000    ~3               ~500        Improved receiver, open loop
                                                             tracking test
GRACE                5/2002     ~5               ~500        RO data not yet available

COSMIC               3/2006     ~5            2500 - 3000    Real time-ops

RoadRunner           11/2005 ~1+                 ~350        Spacecraft in Test – waiting on
USAF                 (slated, Falcon LV)                     rocket and next years fiscal dollars
TerraSAR-X, German   8/2006     ~5               ~400        COSMIC RX & Antennas
EQUARS               ~ 2009     ~3               ~400        COSMIC RX & CHAMP
Brazilian/Japanese                                           antennas, funding not yet secured
                                                             by INPE,
METOP                5/2007     ~5               ~500        Real time - ops

COSMIC II            3/2009     ~5            2500 - 3000    Real time-ops. Ionosphere
              Distribution of GPS Occultation events in 24 hrs with
              EQUARS (2009, inclination angle<20o) and COSMIC
              (2006, 6 LEO satellites at 72o)

                                                                      COSMIC
EQUARS




                                          +
    Dense data rate in
    equatorial region                                                 Global coverage,
                                                                      but less data at
                                                                      low latitudes




                                            o: EQUARS
                                            o: COSMIC
Space - based GOS




           KALPANA (India) &

				
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