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SLA consistency between Jason-1 and TOPEX/Poseidon data

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

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SLA consistency between Jason-1 and TOPEX/Poseidon data

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

  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. No SSB, Old orbits Old ranges 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, New orbits Old ranges -2 cm +2 cm

  4. 2 - Impact of new range : TOPEX • Jason-1 and TOPEX SLA are more homogeneous with the TOPEX LSE range : SSB discrepancies are reduced • Impact of new TOPEX LSE range : • Patches are strongly reduced Use of TP LSE range No SSB, New orbits MGDR TP, MLE3 J1 No SSB, New orbits LSETP, MLE3 J1 -2 cm +2 cm -2 cm +2 cm

  5. +2 cm -2 cm (TP - J1)= - 7.6 cm -2 cm +2 cm 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 Use of Jason-1 MLE4 range No SSB, New orbits LSETP, MLE3 J1 No SSB, New orbits LSE TP, MLE4 J1

  6. (TP - J1)= - 7.6 cm 3 - Impact of new SSB • 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. • 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. Use of new SSB No SSB, New orbits LSETP, MLE4 J1 New SSB,New orbits LSE TP, MLE4 J1 -2 cm +2 cm -2 cm +2 cm

  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 • Equatorial band is visible : • due to hemispheric bias when separating ascending and descending passes. +2 cm -2 cm

  8. 4 - Hemispheric bias Ascending passes • 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 Descending passes +2 cm -2 cm

  9. GDR ‘A’ / MGDR 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. Variance=7.37 cm² ( 2.71 cm RMS) ó 0 cm² 20cm² GDR ‘B’ / RGDR Variance=5.31 cm² ( 2.30 cm RMS) ó 20cm² 0 cm²

  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

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