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SSB – Rtk splinter session 2007-2008 perspectives

SSB – Rtk splinter session 2007-2008 perspectives. 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

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SSB – Rtk splinter session 2007-2008 perspectives

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  1. SSB – Rtk splinter session2007-2008 perspectives

  2. 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 • 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 OSTST Hobart 2007

  3. Questions • 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 an agreement today on the reprocessing specifications for both TOPEX and Jason-1, so we can go ahead with the full reprocessing this year. OSTST Hobart 2007

  4. Jason-1 reprocessing • MLE4 retracking ready; • SSB ready ( or a new version shal be computed if orbit changes) • C-band, ionosphere: ready (additional validation should be performed) • Orbit, JMR -> see other splinters: will be ready this year • note that LSE applied on Jason does not differ sensibly from MLE4 • Jason MLE4 and Topex LSE are now very consistent: no apparent wave dependency, similar SSB models. OSTST Hobart 2007

  5. Reprocessing perspectives for TOPEX • What is ready: • LSE retracking algorithm (range, SWH, Sigma0, att, skewness or not) • Note: the skewness does not eliminate all quadrant features. • PTR characterization • What would need some additional work • SSB model (requires retracked data, orbit, corrections) • Correction for quadrant effects: 3 options: • Add a field with an empirical correction (a+b.SWH) by quadrant, the SSB field being the TOPEX global SSB • Add a field with an empirical correction (a+bSWH) by quadrant, the SSB field being the Jason-1 latest SSB model • Split the SSB model into quadrant • Alt-A SSB from agreement of 1-3 year average • MAP algorithm ? • C-band, ionospheric correction has to be validated OSTST Hobart 2007

  6. Other points • Need to investigate the leakages characteristics, as they now become the main source of error in TP/Jason consistency (~1-2cm) • MAP algorithm • Skewness set to 0 in LSE for SWH<1m => is there an impact? • Sigma 0 LSE has to be in the future reprocessed TP products; more generally, are there requirements/suggestions on the content of those products • Poseidon 1 ? OSTST Hobart 2007

  7. Use of new orbits (GRACE) Use of new orbits (GRACE) Use of new orbits (GRACE) New SSB, range, orbits Orbit : J1-CNES/TP-GSFC 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 New SSB,New ranges Orbit : J1-GSFC/TP-GSFC +2 cm -2 cm

  8. The best we can do now Orbit – Range (GSFC orbits) Delta(J-TP) 1 cm 5 cm 9 cm 5 cm 9 cm 5 mm 5 cm 9 cm 5 cm 9 cm Orbit – Range - SSB (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

  9. Jason SSB (95-131) Topex LSE (328-364) -30 cm -30 cm 0 cm 0 cm Both SSB are estimated on a full year of data. Cycles 1-21 are not enough to assess accurately the sea state variations.

  10. -3 cm +3 cm Mean crossovers SSH using MGDR GSFC orbits [cm] Mean of Topex SSH differences at Xovers: Range impact LSE & GSFC orbit • Hemispheric bias increases using LSE and MAP retracking • Since LSE retrieves 5 parameters instead of 4 (MGDR), noise on altimetric parameters is increased MGDR GSFC orbit Mean HN : -0.89 cm HS: 1.07 cm -3 cm +3 cm Mean HN : -0.58 cm HS: 0.68 cm Mean crossovers SSH using LSE & GSFC orbit [cm] MAP & GSFC orbit Mean HN : -0.93 cm HS: 1.37 cm -3 cm +3 cm Mean crossovers SSH using MAP & GSFC orbit [cm]

  11. Status • 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)

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