OSTST ‘07 Retracking and SSB Splinter Report. Juliette Lambin and Phil Callahan March 14, 2007 Hobart, Tasmania. OSTST Retracking & SSB Splinter – Overview. Discussion
Juliette Lambin and Phil Callahan
March 14, 2007
Jason Skewness Cyc 19-21 (avg = 0.06)
As with Jason, LSE and MAP retrackers exhibit a SWH dependence difference.
In order to make TOPEX and Jason compatible at the 1cm level, the waveform leakage contamination be mitigated.
TOPEX LSE-GDR (toward) Vs Att / SWH
-20 Range difference (mm) 30
Jason LSE-MAP vs Att / SWH
TOPEX LSE-MAP(toward) vs Att / SWH
0 Range difference (mm) 40
CNES dh = -[ku_range + ku_range_20Hz - (ku_tracker20Hz + total_instr_correction)]
There appears to be a discontinuity at the equator which is different for ascending and descending passes
Equatorial discontinuity present and more marked
Equatorial discontinuity present, notice change in bias value = 8mm
TOPEX and Jason Retracking
There appears to be a SWH dependent bias between MAP and LSE, but no apparent discontinuity at the equator
There appears to be a SWH dependent bias between MAP and LSE, as in Topex. However, differences seem to be larger
Averaging Time: 40 seconds
Due to onboard signal leakages, TOPEX waveforms are contaminated by spurious signals which appear in the leading edge and are hard to model.
Rodriguez and Martin (JGR, 1994) estimated height biases of ~+/-1 cm which were geographically dependent by comparing with LSE retracking.
Maximum Likelihood Estimator (MLE) Minimizes:
Maximum a Posteriori (MAP) Minimizes:
Where x is the data, a are the parameters to be estimated, A are the parameter a priori values, si are the measurement errors and Sn measures the prior confidence level. Setting the priors and their confidence levels is the trick!
Prior Values: smooth LSE SWH and attitude data over an extent < 80 km relative to center
Prior Uncertainties: Root Squares Sum residual values in smoothing window with conservative estimate of minimum uncertainty of SWH and attitude variance. Use 1.5 as uncertainty on the skewness, and infinite variances (no priors) on the other parameters, including height.