Recent Radio Occultation Analysis Results from the

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Recent Radio Occultation Analysis Results from
the COSMIC Data Analysis and Archival
Center (CDAAC) Bill Schreiner, Doug Hunt, Chris
Rocken, Sergey Sokolovskiy COSMIC Project Office
- GST UCAR
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Outline

• Overview/Status of CDAAC processing
• POD Results
• Calibration via single/double differencing
• Validation Statistics

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CDAAC Responsibilities

• Process all COSMIC observations
• GPS/LEO orbits
• Atmospheric Ionospheric profiles
• Rapid analysis for operational demonstration
• Post-processed analysis for climate and other
  research
• Provide data to universities and research
  laboratories
• Provide data feeds to operational centers
• Archive data provide web interface

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CDAAC Processing Flow
Atmospheric processing
Moisture correction
LEO data
Level 0--level 1
Excess Phase
Abel Inversion
Orbits and clocks
Fiducial data
Real time Task Scheduling Software
Profiles
Ionospheric processing
Combination with other data
Excess Phase
Abel Inversion
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CDAAC Processing Status

• Processing GPS/MET (1,156 occs), CHAMP (30,482
  occs), and SAC-C (21,691 occs) in post-processed
  mode of operation
• double differencing for excess delay calibration
• Canonical Transform (Gorbunov, 2001,2002) used in
  lower troposphere inversion
• 1D-VAR moisture retrieval
• Abel inversion in ionosphere
• Recent (2002.091-097) tropo retrieval success
  (70 OK, 20 no calibration, 10 thrown out due
  to QC)
• Correlative Data (NCEP, ECMWF, Radiosondes)
• All data being archived - available on web

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GPS Processing

• Bernese GPS software v4.2 (preliminary version of
  LEO POD software, v4.3)
• First estimate ground-site ZTD for 40-50 station
  network
• Estimate 30-second GPS clocks
• Estimate kinematic LEO orbit
• LEO Dynamic Modeling
• EIGEN-S1 Gravity model
• Drag (MSISE90 air density, cannon ball drag
  model)
• Constant and 1-cycle/revolution empirical
  accelerations
• Accelerometer/Attitude data not currently used
  for CHAMP non-conservative force modeling

- GPS Orbits/ERP (Final/IGU) - Station
Coordinates - 30-sec Ground GPS Obs.
Estimate Ground-site Tropospheric Delay
Estimate 30-sec GPS Clocks
Estimate Kinematic LEO Orbit
Dynamically Smooth Kinematic LEO Orbit
- 1-Hz Ground GPS Obs. - 50-Hz LEO Occultation
GPS Obs.
Double Difference Occultation Processing
Precise Atmospheric/Ionospheric Excess phase
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LEO POD Quality
CHAMP-A (EIGEN-S1) minus CHAMP-B
(EGM96) Temperature profiles
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Calibration of excess delay

• Double Difference
• Advantage Clock errors removed
• Problem Fid. site MP, atmos. Noise, thermal
  noise
• Single Difference
• LEO clock errors removed
• use solved-for GPS clocks
• Main advantage Minimizes double difference
  errors
• Wickert et al. (2002) used IGS 5 min GPS clocks
  (no high-rate ground data)

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Single vs. Double Differencing
DD - SD (5min clocks)
DD - SD (1sec clocks)

• improvement from 1K to 0.5K in standard
  deviation in temperature at 30 km
• DD and SD(1sec clocks) profiles agree slightly
  better w/ NCEP than SD(5min clocks) profiles (2
  in s.d of temperature at 30 km)

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Validation Statistics

• RO profiles compared to weather model
• Comparisons to NCEP-NCAR Global Re-analyses (6
  hr, 28 sigma levels, 1.87deg longitude, 94
  gaussian latitudes, ds090.0)
• Interpolate model to RO time and location
• Quality controlled RO profiles

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Validation Statistics
Global
CHAMP
SAC-C

• Mean percent difference lt 1 from 1 to 30 km
• Penetration to 1 km, CHAMP 48 , SAC-C 42

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Validation Statistics
CHAMP Tropics
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CHAMP/NCEP binned stats
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Validation Statistics
Near St. Helena Is.
Near Kwajalein
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Summary

• CHAMP and SAC-C processing up-to-date
• 70 of tracked occultations are inverted
  successfully (2002.091-097)
• CHAMP POD at 30 cm 3D rms level, should improve
  to 10 cm with Bernese v5.0
• SD processing being investigated
• CHAMP and SAC-C compare well with NCEP
• N-bias in lower troposphere, super-refraction