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

Mars/MRZ       VIZ

                         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

     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
  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
    – No more instrumental bias in the lower
    – >50% of soundings penetrate into lowest
   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
 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)


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

                                            o: EQUARS
                                            o: COSMIC
Space - based GOS

           KALPANA (India) &