1. Evaluation of the ground retracking algorithms on Jason-1 data P.Thibaut, S. Labroue Collecte Localisation Satellite : Toulouse, France

2. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 2 Objective  The objective of this presentation is to characterize the various retracking algorithms applied on Jason and Topex waveforms and to determine if they can be considered as responsible for differences observed between Jason and Topex SSB.  We decided to apply the various retracking on Jason-1 WFs. If no differences are observed when retracking the same waveforms, the differences between Topex and Jason SSB may directly come from the WFs (leakages on Topex WFs) All the results presented have been obtained on one cycle of Jason-1 data (cycle 20) GDR ‘B’ nominal Jason-1 products Retracked files provided by JLP (same information than in Topex RGDRs including LSE and MAP estimations)

3. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 3 Characteristics of the 3 retracking algorithms MLE4 (nominal proc. for GDRs) : LSE MAP Epoch, SWH, Pu, slope of the trailing edge : 20 estimations per second Retracking a single gaussian + LUT which provide the correction between one gaussian and the full real PTR (as a function of SWH) Skewness s set to 0.1 Waveforms averaging (2x2 in Ku band, 4x4 in C band) before retracking Decomposition of the PTR into a sum of Gaussians (for 20 side-lobes) Epoch : 10 estimations per second in Ku (5 in C) SWH, Pu, slope of the trailing edge : 1 estimation per second s : 1 estimation per second or fixed to 0 Idem LSE Allows comparison to Topex LSE Allows comparison to Jason MLE4 (except that for Jason a 0.1 value is used)

4. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 4  Range 1Hz = Tracker GDR – Epoch JPL – LUT GDR – Range GDR_1Hz Information provided by the various products JPL products provide: the retracked epoch (10 Hz and 1 Hz) (JPL = LSE or MAP) : Epoch JPL GDR products provide: the range (20 Hz and 1Hz) : Range GDR the tracker range (20Hz and 1 Hz) : Tracker GDR the Look Up Table correction for epoch (1Hz) : LUT GDR Comparison between JPL and GDR ranges is given by:  Range 1Hz = Range JPL_1Hz – Range GDR_1Hz But we have only the Epoch JPL

5. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 5 Delta Range(LSE - GDR) versus (SWH and SIG0) 40 cm50 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

6. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 6 Delta Range(LSE - GDR) versus (SWH and ATT 2 ) 40 cm50 cm  No remaining dependancies with SWH or ATT 2 in the bulk of the data Range_LSE-Range_GDR versus (SWH,ATT) Skew solved  Skewness solved

7. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 7 Delta Range(LSE - 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 cm50 cm 40 cm50 cm

8. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 8 SWH LSE-GDR MAP-GDR SWH ATT2  Range  Very good agreement between LSE and MLE4  MAP introduces SWH and ATT dependances (Constraints on MAP skewness is too strong : s=0) Skewness solved 45 cm 50 cm 45 cm 50 cm 1%SWH

9. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 9 Delta Range(MAP - GDR) versus (SWH and SIG0 and ATT2)  MAP introduces dependances but the skewness remains close to 0 (in GDR 0.1)  Same kind of plot when skewness fixed at 0 Range_MAP-Range_GDR versus (SWH,ATT) Skew solved Range_MAP-Range_GDR versus (SWH,SIG0) Skew solved 40 cm50 cm40 cm50 cm

10. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 10 Difference of range (LSE – MAP) -5cm+5cm

11. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 11 Skewness estimation LSEMAP  Skewness is not estimated for SWH smaller than 1 m  Skewness remains close to 0 for MAP Mean=0.06Mean=0.001

12. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 12 Skewness with respect to SWH LSEMAP  Skewness is not estimated for SWH less than 1 m  Skewness remains close to 0 for MAP

13. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 13 ATT_LSEATT_MAPATT_GDR  ATT(LSE-GDR)  ATT(MAP-GDR) Statistics on ATT – Skewness Solved Mean=-0.002Mean=-0.003 Mean=0.003Mean=0.001

14. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 14 Statistics on SWH  SWH(LSE-GDR)  SWH(MAP-GDR) Skewness solved Skewness fixed Mean=7.64 cmMean=7.91 cm Mean=28.8 cmMean=7.06 cm

15. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 15 Jason-1 SLA Power Spectrum J1 LSE5 TP LSE5 J1 MLE4 (GDRB) J1 LSE4 (fixed skew)  Very good coherence between Topex LSE5 and Jason MLE4  Between MLE4 and LSE4, impact of 1HZ estimation for SWH, Pu and Att2 (skew fixed for both)  Between LSE4 and LSE5, impact of the estimation of a 5 th parameter ( s)  Between MLE4 and LSE5, addition of the two previous effects (it has been shown that they are very close regarding the SSB) (see Faugere’s talk)

16. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 16 Conclusions LSE and MLE4 algorithms are equivalent wrt SSB when skewness is solved for. SSB differences between Topex and Jason cannot be explained by differences in the retracking algorithms SSB differences lie in the WFs themselves SWH biases (LSE) are still to be analysed MAP is not yet ready to provide users with reliable estimates Range_LSE-Range_GDR versus (SWH,SIG0) Skew solved

17. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 17

18. Simulator of Interferometric Radar Altimeters concept and first results P. THIBAUT, B.PICARD : CLS, France, O.GERMAIN : Starlab, Spain, F.COLLARD : Boost-Technologies, France L.PHALIPPOU : Alcatel-Alenia-Space, France C.BUCK5 : ESTEC-ESA, The Netherlands PRF - 1 V sat Left swath Right swath Nadir track Sea State Modelling Waveform generation Boost Starlab Interferometric Inversion CLS

19. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 19

20. Hobart OSTST Meeting Pierre THIBAUT – March 2007 Page 20 Sigma-0 blooms in the Envisat Radar Altimeter data P.THIBAUT, F.FERREIRA : CLS, France, P.FEMENIAS : ESA/ESRIN, Italy Which one is a bloom, which one is not ? Where are the egdes ? What are their length ? Where are they ? What about the waveforms during blooms ? What are the impact of blooms on ranges ? How many blooms are edited by Calval criteria? Which kind of criteria would be more useful ? …. Ideas, comments …. Come to talk with me.