ssb – retrack splinter summary and 2007-2008 perspectives
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SSB – Retrack Splinter Summary and 2007-2008 Perspectives. OSTST Hobart, Tasmania March 15, 2007. Sea State Bias and Retracking Analysis Splinter. Talks: 0930 D. Vandemark, H. Feng, N. Tran, B. Chapron, B. Beckley Inclusion Of Wave Modeling In Sea State Bias Correction Refinement - PowerPoint PPT PresentationTRANSCRIPT
SSB – Retrack Splinter Summary and SSB – Retrack Splinter Summary and 2007-2008 Perspectives2007-2008 Perspectives
OSTST Hobart, Tasmania
March 15, 2007
OSTST Hobart 2007 22007/03/15 jl+psc
Sea State Bias and Retracking Analysis SplinterSea State Bias and Retracking Analysis Splinter
■ Talks: ■ 0930 D. Vandemark, H. Feng, N. Tran, B. Chapron, B. Beckley Inclusion Of Wave Modeling In Sea State Bias Correction
Refinement■ 0950 E. Rodriguez, P. Callahan, T. Lungu Cross Calibration Of TOPEX And Jason Using MAP And LSE Retracking To
Improve Global Sea Level■ 1010 P. Thibaut, S. Labroue, N. Granie Evaluation Of Ground Retracking Algorithms On Jason Data■ 1030 BREAK■ 1100 Y. Faugere, A. Olivier, P. Thibaut, G. Dibarboure, N. Picot, J. Lambin Analysis Of The High Frequency Content Of
Jason-1, Topex And Envisat Data ■ 1120 S. Labroue, M. Ablain, J. Dorandeu, N. Tran, P. Gaspar, O.Z. Zanife Comparison Of Topex And Jason-1 Sea State
Bias Models ■ 1140 Discussion
■ Posters:■ SSB-P1. TOPEX Retracked GDR – Features and Statistics, Philip S. Callahan, Ernesto Rodriguez, Ted Lungu ■ SSB-P2. A New Altimeter Waveform Retracking Algorithm Based On Neural Networks, Arnaud Quesney, Eric Jensou,
Juliette Lambin, Nicolas Picot ■ SSB-P3. Unsupervised Classification Of Altimetric Waveform Over All Surface Type, Arnaud Quesney, Eric Jeansou,
Christian Ruiz, Nathalie Steunou, Bruno Cugny, Nicolas Picot, Jean-Claude Souyris, Sylvie Thiria, Mustapha Lebbah ■ SSB-P4. Sigma0 Blooms In The Envisat Radar Altimeter Data, Pierre Thibaut, F. Ferreira, Pierre Femenias ■ SSB-P5. Simulator Of Interferometric Radar Altimeters: Concept And First Results, Pierre Thibaut, Olivier Germain,
Fabrice Collard, Bruno Picard, Laurent Phalippou, Christopher Buck
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OutlineOutline
■Brief review of presentations
■Review of discussion on JPL, CNES retracking and SSB
■We want to come to agreement today on the reprocessing approach for both TOPEX and Jason-1, so we can go ahead with the full reprocessing this year:
Would like endorsement of proposed approach
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APPROACH
Driving Assumption – information on wave steepness from global wave model can be integrated with altimeter Hs and U10 to improve routine sea state range corrections
TRACK 1 Nonparametric global SSB solutions using 2 input variables – SLA averaging method
Inputs are [ Hs, family of alternatives ]
Tran et al., 2006 JGR - methods and 1st results
TRACK 2 Three step clustering approach
Partition measurements using fuzzy clustering
Develop multi-class SSB solutions
Combine to give single global result
Vandemark et al.
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Figure 7. Hard partition (max membership) class-specific direct SSB maps on U10 and Hs domain for 2000, 2001, and 2002. from TOPEX+ WW3-ecmwf (NASA-GSFC Pathfinder datasets: 1/10 of the total points) (200 samples in a cell)
2000 2001 2002
Vandemark et al.
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Jason-1 2004 results using clustering-based NP SSB solution (6 classes)
• Systematic improvements at all latitudes and most regions in the spatial benchmark at right• Not optimized yet so results will improve
Vandemark et al.
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Signal hidden by noise
Noise hidden by oceanic signal Noise
Spectrum of oceanic signal s
Plateau
A plateau on a power spectrum can be the signature of a white noise.
Method and data usedMethod and data used
■ First method: spectral analysis of the SLA signalSLA(t) = s(t) + (t) , where s(t) is the geophysical
signal and (t) is the noise
• 1Hz spectra are computed from 10 days of data• 20Hz spectra are computed from 2 days of data
Y. FaugereHigh Frequency Content
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Cross comparison of Jason-1 and EnvisatCross comparison of Jason-1 and Envisat
Impact of SWH selection on HF content
1Hz Data 20Hz Data
Legend:
High SWH EN
High SWH J1
Small SWH EN
Small SWH J1
• 1Hz Envisat and Jason-1 are superimposed in both cases. The noise level increases with the wave height. Moreover a sort of pseudo-plateau is visible on 1Hz spectra at 1Hz only for high waves• At 20hz Envisat and Jason-1 spectra are closer for small waves (plateau almost superimposed). •The pseudo-plateau visible at 1Hz on high waves is not the signature of a instrumental white noise. It is the signature of the energy between 0.1-0.4Hz on the 20Hz spectra
Y. Faugere
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First results on the cross comparison of Jason-1 and First results on the cross comparison of Jason-1 and Topex RGDR HF contentTopex RGDR HF content
TP MAPTP LSEJ1 MLE4
Variance difference of HF content:J1 MLE4 (cycle 20) - TP LSE (Cycle 360)
-1cm² 1cm²
• TP LSE and J1 MLE4 1Hz spectra are very consistent
•The Geographical distribution of the difference of HF content is not as homogeneous as for Jason-1/Envisat
Y. Faugere
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Retracking Progress Retracking Progress
■Retracked 2 yr TOPEX Alt-B and produced RGDRs with improved orbits
LSE skewness absorbs WF leakages so much reduced N/S Asc/Des (“Quadrant”) difference, but still some
MAP skewness much smaller so large variations with SWH Need to assess waveform residuals to correction for leakages, OR rely on
empirical correction
■Worked issues with CNES on differences of MLE4, LSE, MAP Processed large set of simulated data, numerous PTRs Found no anomalies in Jason waveform residuals However, MLE4 only agrees with LSE when solve for skewness, not
fixed skewness. MAP has SWH dependence Similar results found from simulated WF
Rodriguez et al.
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TOPEX Waveform Contamination EvidenceTOPEX Waveform Contamination Evidence
TOPEX Skewness Jason Skewness Cyc 19-21 (avg = 0.06)
Des
Asc
Rodriguez et al.
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 12
Delta Range(TPX LSE – Jas GDR) versus (SWH and SIG0)
40 cm 50 cm
No remaining dependancies with SWH or SIG0 in the bulk of the data
Skewness solved Range_LSE-Range_GDR versus (SWH,SIG0)
Skew solved
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 13
Delta Range(TPX LSE - Jas GDR) versus (SWH and ATT2)
40 cm 50 cm
No remaining dependancies with SWH or ATT2 in the bulk of the data
Range_LSE-Range_GDR versus (SWH,ATT) Skew solved
Skewness solved
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 14
Delta Range(TPX LSE – Jas GDR) versus (SWH and SIG0 and ATT2)
Dependances appear when the skewness is fixed but it was fixed to 0 (in GDR 0.1)
Range_LSE-Range_GDR versus (SWH,ATT) Skew fixed
Range_LSE-Range_GDR versus (SWH,SIG0) Skew fixed
40 cm 50 cm 40 cm 50 cm
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 15 -
Orbit – Range (GSFC orbits)
Good global results but some sea state related signals are still there when comparing the quadrants.A SSB estimated globally on Topex cannot remove all the residual sea state dependences
Orbit – Range - SSB (GSFC orbits)
5 cm 9 cm5 cm 9 cm
5 cm 9 cm 5 cm 9 cm
1 cm
5 mm
Delta(J-TP)The best we can do now S. Labroue
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 16 -
Jason SSB (95-131)
Both SSB are estimated on a full year of data. Cycles 1-21 are not enough to assess accurately the sea state variations.
Topex LSE (328-364)
-30 cm 0 cm -30 cm 0 cm
S. Labroue
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QuestionsQuestions
■Do retracking approaches show reduction in SSB?
■What is the approach to aligning TOPEX and Jason data?
■What error model should be used with the corrected data?
■We want to come to agreement today on the reprocessing approach for both TOPEX and Jason-1, so we can go ahead with the full reprocessing this year:
Would like endorsement of proposed approach
OSTST Hobart 2007 182007/03/15 jl+psc
Jason-1 ReprocessingJason-1 Reprocessing
■MLE4 retracking ready LSE applied on Jason does not differ sensibly from MLE4 Jason MLE4 and Topex LSE are now very consistent: no apparent SWH
dependence, similar SSB models
■SSB processing ready, so a new version will be computed as soon as other pieces, e.g., final CNES orbit, is available
■C-band, ionosphere: ready. Additional validation may be performed
■ Orbit, JMR: will be ready this year (-> see other splinters)
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TOPEX Reprocessing TOPEX Reprocessing
■ Propose to use LSE retracking algorithm including skewness Note: skewness does not eliminate all quadrant features. PTR fitting program (mainly for Alt-A) exists but needs updating
■ Needs some additional work SSB model (requires retracked data, orbit, corrections ) – CNES will fit on
RGDR; final RGDR updated with SSB C-band, ionospheric correction has to be validated Correction for quadrant effects, 3 options:
1. Add a field with an empirical correction (a+b.SWH) by quadrant, the SSB field being the TOPEX global SSB
2. Add a field with an empirical correction (a+bSWH) by quadrant, the SSB field being the Jason-1 latest SSB model
3. Split the SSB model into quadrant Splinter had some preference for #1. Endorsement ?
Alt-A SSB from agreement of 1-3 year average
■ JPL plans to complete reprocessing within approx 1 yr (may need some extension into next OSTST)
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Other PointsOther Points
■Should investigate the leakages characteristics, as they now become the main source of error in TP/Jason consistency (~1-2cm)
But, proposed approach will correct empirically with quadrant SSB
■MAP algorithm appears not to provide good results on either Jason or TOPEX: small skewness, SWH dependence of height
■Skewness set to 0 in LSE for SWH<1m => is there an impact? Very difficult to solve; inversion tends to be unstable
■Poseidon 1 ?
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Backup Material Backup Material
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Method and data usedMethod and data used
■ Second method: Filtering technique
HF(SLA)
High-pass filter (20km cut-off)
SLA=Orbit-Range-MSS
σ[HF(SLA)] in 2°x2° boxes
Standard deviation
2007 OSTST meeting- 22 -
Y. Faugere
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 23 -
(TP- J 1)=- 6.9 cm
(TP- J 1)=- 7.1 cm
4 - Impact of GSFC orbit
• New orbits are provided by CNES for Jason-1(GDR ‘B’) and GSFC for TOPEX (RGDR).
• Using GSFC orbits similar for Jason-1 and TOPEX, allows us to remove the East/West signal
Even if orbits are best and more homogenous between TOPEX and Jason-1, weak systematic discrepancies remain (< 1cm).
-2 cm
-2 cm
+2 cm
+2 cmUse of new orbits (GRACE)Use of new orbits (GRACE)Use of new orbits (GRACE)
New SSB, range, orbitsOrbit : J1-CNES/TP-GSFC
New SSB,New rangesOrbit : J1-GSFC/TP-GSFC
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 24 -
4 – SLA Consistency J1/TP (LSE) • Does new retracking methods make SLA of Jason-1 and T/P more
consistent?
• Using Jason-1 GDR ‘B’ cycles 1 - 21
• SLA without geophysical corrections
LSE range makes SLA of T/P more consistent with J1.
SLA differences J1/TP using TP MGDR range
MGDR GSFC orbit LSE GSFC orbit
-2 cm -2 cm+2 cm +2 cm
SLA differences J1/TP using TP LSE range
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 25 -
4 – SLA Consistency J1/TP (MAP)
SLA differences J1/TP using TP MGDR range [cm]
-2 cm +2 cm
SLA differences J1/TP using TP MAP range [cm]
-2 cm +2 cm
MGDR GSFC orbit MAP GSFC orbit
• Using TP MAP range does not significantly decrease SLA differences between Jason-1 and T/P
S. Labroue
OSTST Hobart 2007 – Performance assessment TOPEX/Poseidon data- 26 -
Mean of Topex SSH differences at Xovers: Range impact
• Using LSE retracking makes T/P ranges more consistent with Jason-1 ranges but residual sea state errors are still present. The errors are quadrant dependent and due to leakages in the TP waveforms.
• Mean SSH differences at crossoverpoints show hemispheric bias, which increases when using retracked data instead of MGDRs (different impact of the leakages as a function of the sign of the range rate)
– Since LSE retrieves 5 parameters instead of 4 (MGDR), noise on altimetric parameters is increased
Mean crossovers SSH using LSE & GSFC orbit [cm]-3 cm +3 cm
Mean crossovers SSH using MAP & GSFC orbit [cm]-3 cm +3 cm
LSE & GSFC orbit
MAP & GSFC orbit
Mean crossovers SSH using MGDR GSFC orbits [cm]-3 cm +3 cm
MGDR GSFC orbit
Mean HN : -0.58 cm HS: 0.68 cm Mean HN : -0.89 cm HS: 1.07 cm
Mean HN : -0.93 cm HS: 1.37 cm
S. Labroue