Ionospheric Error Contribution To GPS Radio Occultation Temperature RetrievalsSI Traceability Applied To GPS Radio Occultation
A. J. Mannucci, C. O. Ao, T. K. Meehan, B. A. Iijima
Jet Propulsion Laboratory, California Institute of Technology
Bill Schreiner, Chris Rocken, Sergey Sokolovskiy
Shu-Peng Ben Ho, Doug Hunt
UCAR COSMIC Project
SI Traceability Applied to GPS RO
Overview of Today’s Talk
The Radio Occultation Measurement
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
The Radio Occultation Measurement
Geometry of an acquisition
• Local spherical symmetry
• Doppler -> refractive index vs altitude
CLARREO Workshop Oct 2008 AJM/JPL
GRACE done this way, but not as SI-traceable as next way
SI Traceability Applied to GPS RO
Applied SI-Traceability
SI Traceability Applied to GPS RO
Role Of Geodetic Modeling
GIPSY (JPL), Bernese (U. Berne), etc.
Satellite and ground locations assumed known
Orbits to ~cm level are demonstrated
GPS time synchronized to atomic time via reference receivers (e.g. USNO)
General relativistic effects, solid Earth tides, UT variation, polar motion, S/C trajectory, troposphere, etc.
Occ duration
See QOCA site for software references
SI Traceability Applied to GPS RO
Retrieval Products From WRF Model
T
q
N
Negligible occurrence
CLARREO Workshop Oct 2008 AJM/JPL
SI Traceability Applied to GPS RO
Advantages Of Self-Calibration
Systematic error cancellation
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Instrumentation: Measuring Phase
Analog Electronics
Digital Electronics
Anecdote: the bad CHAMP clock had no discernable effect.
SI Traceability Applied to GPS RO
Research Issues
In situ mesosphere residual
Improve algorithm and characterization
Monitor in-situ
Retrieval systems must be carefully analyzed and vetted by the community
CLARREO Workshop Oct 2008 AJM/JPL
SI Traceability Applied to GPS RO
Results
CHAMP-SAC-C
Does not directly assess all possible sources of systematic error
CLARREO Workshop Oct 2008 AJM/JPL
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Coincident
Observations
Within
N = 212
Hajj et al., (2004) “CHAMP and SAC-C atmospheric occultation results and intercomparisons”, JGR.
Differences: Median and standard deviation versus separation
Careful accounting for decorrelation with distance
CLARREO Workshop Oct 2008 AJM/JPL
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Soundings From COSMIC – JPL
1 K
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
UCAR COSMIC Results
Refractivity
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Other Results
RO Trends study: analysis of inter-center differences in monthly mean refractivities
JPL, UCAR, GFZ, Wegener Center (Austria)
CHAMP 2002-2007
Varying quality control criteria
Trends determined much better than absolute differences
Different center retrievals have small but fixed offsets that do not vary in time
CLARREO Workshop Oct 2008 AJM/JPL
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Uncertainty of the
trend for fractional refractivity anomalies among centers is within ± 0.04%/5 yrs globally.
JPL, UCAR, GFZ, Wegener Center
Deseasonalized fractional refractivity anomalies
CHAMP
2002-2007
Trade space:
Several sci objectives. Do they compete?
Weather -- need OSSEs
Space Weather -- low latency
Space science -- with only a GPS instrument? Heresy! Bring up C/NOFS
Various tropo science objectives
Summary
Radio occultation is a geodetic technique for measuring climate trends
Physics of the measurement is highly advantageous
Self-calibrating time delay measurements yield high quality SI-traceable accuracy
Accuracy implies stability
Negligible inter-satellite biases
“Climate index tied to atomic clock standards”
CLARREO provides data we urgently need for the long term climate record
Research is ongoing to fully quantify all sources of systematic error that do not completely difference out
CLARREO Workshop Oct 2008 AJM/JPL
Dykema quote: