1. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 1 - SLA consistency between Jason-1 and TOPEX/Poseidon data M.Ablain, S.Philipps, J.Dorandeu, - CLS N.Picot - CNES

2. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 2 - Introduction Jason-1 and TOPEX data have been reprocessed over the tandem period (Jason-1 cycles 1 to 21, TOPEX cycles 344 to 364) Evolutions in J1 GDR “B” and T/P RGDR: –New orbits based on GRACE gravity model –New retracking algorithms (MLE4 for Jason-1, MLE5 & MAP for TOPEX) –Updated or new geophysical corrections (tidal models, DAC HF correction, …) Objective : check the impact of the reprocessing on the sea surface height consistency (SLA) between Jason-1 and TOPEX Objectives: –Impact of new orbits on SLA consistency –Impact of new range on SLA consistency –Impact of new Sea State Bias on SLA consistency

3. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 3 - 1 - Impact of new orbits Raw SLA differences between TOPEX and J1 : –SSH not corrected for geophysical corrections => T/P & Jason-1 on the same pass with a delay of 72s. –SSB is not applied Use of old orbits : –Large structures appear : North Atlantic, Indonesia => (+/- 5 cm) –Trackiness strongly visible Use of new orbits allows to : –Remove trackiness –Strongly reduce Patterns in North Atlantic and Indonesia –Evidence new structures partly explained by SSB discrepancies -2 cm +2 cm No SSB, Old orbits Old ranges No SSB, New orbits Old ranges

4. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 4 - 2 - Impact of new range : TOPEX Impact of new TOPEX LSE range : –Patches are strongly reduced -2 cm +2 cm-2 cm +2 cm No SSB, New orbits MGDR TP, MLE3 J1 No SSB, New orbits LSE TP, MLE3 J1 Use of TP LSE range  Jason-1 and TOPEX SLA are more homogeneous with the TOPEX LSE range : SSB discrepancies are reduced

5. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 5 - 2 - Impact of new range : Jason-1 Impact of new Jason-1 MLE4 range : –weak impact on the mean differences, –the consistency is slightly better in the Indian Ocean -2 cm +2 cm -2 cm +2 cm (TP-J1)=-7.6 cm Use of Jason-1 MLE4 range No SSB, New orbits LSE TP, MLE3 J1 No SSB, New orbits LSE TP, MLE4 J1

6. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 6 - 3 - Impact of new SSB New SSB corrections have been computed –Jason-1 : Labroue, Venice 2006 –TOPEX : collinear method using RGDR (LSE) => Labroue’s talk. These new TOPEX and J1 SSB models are now much closer than before. -2 cm +2 cm (TP-J1)=-7.6 cm Discrepancies between J1 and T/P are further reduced when applying these new SSB models in the SLA calculation, in addition to the new orbits. However, an East/West patch (< 1cm) remains, but it is not correlated with SWH. Use of new SSB No SSB, New orbits LSE TP, MLE4 J1 New SSB, New orbits LSE TP, MLE4 J1 -2 cm +2 cm

7. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 7 - 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 Use of new orbits (GRACE) New SSB, range, orbits Orbit : J1-CNES/TP-GSFC New SSB,New ranges Orbit : J1-GSFC/TP-GSFC Equatorial band is visible :  due to hemispheric bias when separating ascending and descending passes.

8. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 8 - 4 - Hemispheric bias A strong hemispheric bias (between -2 cm and +2 cm) is highlighted when separating ascending and descending passes. Bias mainly due to TOPEX data. Present on TOPEX M-GDR data but not easily detectable with former orbits  Waveform leakage problem explains this hemispheric effect. Use of new TOPEX LSE range increases this ascending/descending effect -2 cm +2 cm Ascending passes Descending passes

9. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 9 - 5 - Variance of SLA differences Variance of Jason-1/TOPEX SLA differences computed after filtering out SLA signals smaller than 50 km (in order to remove the SSH high frequency content). Using GDR ‘A’ for Jason-1 and MGDR for T/P : – variance is about 7.4 cm² – larger differences in strong waves areas due to SSB discrepancies Using GDR ‘B’ for Jason-1 and RGDR for T/P: –variance is reduced by 2 cm² –Variance is mainly reduced in strong wave areas showing the better SSB consistency between Jason-1 and T/P. 0 cm²20cm² GDR ‘A’ / MGDR GDR ‘B’ / RGDR 0 cm² 20cm² Variance=5.31 cm² (  2.30 cm RMS) Variance=7.37 cm² (  2.71 cm RMS)

10. OSTST Hobart 2007 – SLA consistency between Jason-1 and TOPEX data - 10 - Conclusion T/P / Jason-1 SLA consistency show large improvements : –from new orbits for both TOPEX and Jason-1 Reduction of apparent trackiness New signals can now be detected (SSB differences, North/South – ascending/descending signals on TOPEX) Weak East/West signal (< 1cm) have been evidenced between CNES and GSFC orbits –from new TOPEX retracking : strongly reduces the differences between TOPEX and Jason SSB –from new SSB : SSB estimations are now much more consistent SLA discrepancies remain : –Large ascending/descending hemispheric signals still remain in TOPEX data due to leakage waveform problem –LSE range seems more impacted by this leakage problem than the MGDR range