Local and global calibration/validation P. Bonnefond, S. Desai, B. Haines, S. Nerem and N. Picot

1. Local and global calibration/validation P. Bonnefond, S. Desai, B. Haines, S. Nerem and N. Picot ? Jason-1 - T/P Sea Surface HeightFormation Flying Phase (Jason-1 Cycles 1-21)

2. Long-Term Sea-Surface Height Bias Estimates Nominal (T/P: MGDR-B+TMR+GSFC TVG; Jason-1: GDR-B) Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session Haines et al.

3. Jason-1 GDR SSH remains biased (high) New GDR-B reduces bias (2002.0 epoch) from +112 to +81 mm. New POE in GDR-B improves the standard deviation. No significant drift in Jason-1 bias (GDR-B) Drift due to JMR wet path delay is removed (Senetosa wasn't affected by GDR-A orbit). No detectable drift in JMR path delay ~14 mm bias in JMR GDR-B remains (compared to GPS). ~19 mm / ECMWF. Suggests JMR is too short at Senetosa. Explains half of the Harvest/Senetosa difference. Biases (SSH) in T/P altimetric measurement decreased with MGDR+ 3 mm due to TMR replacement product (and 6mm more when compared to the old TMR correction). -10mm due to the new GSFC orbits (included in the Retracked GDR products) Insignificant drift for ALT-B in T/P altimeter measurement systems T/P retracking increases the bias (less negative) +13 mm for RGDR-1 (LSE) and +6 mm for RGDR-2 (MAP). MAP (RGDR-2) retracking gives more noisy results than LSE (RGDR-1) one (standard deviation of 42 mm and 32 mm respectively). Numbers should be revised when new SSB and ionospheric corretion will be delivered CONCLUSION ALT-B (MGDR+): Bias 2002.0 = -23 ±5 mm (-5 ±5) Slope = -1 ±3 mm/yr (-2 ±3) POSEIDON-2 (GDR-B): Bias 2002.0 = +81 ±9 mm(+114 ±6) Slope = +1 ±3 mm/yr(0 ±2) Corsica Results (Harvest results): ALT-A (aging): -8 ±9 mm (-7 ± 3) ALT-B: -22 ±3 mm (-3 ±4) POSEIDON-2: +84 ±4 mm (+115 ±3) Bonnefond et al. OSTST Meeting, Hobart, March 2007

4. Average of Differences w.r.t. Independent Measurements • JMR comparisons to SSMI, TMI, and GPS statistically identical. • TMR comparisons to GPS are biased by ~ -9 mm versus SSMI and TMI. • Separation of GPS comparisons by island and continental sites shows large discrepancy for TMR, but not for JMR. • TMR likely dominant source for errors near continents. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session Desai et al.

5. Further improvement expected using similar treatment for: Geographically correlated orbit errors, ALT-B waveform leakage, SSB correction… Haines & Bonnefond

6. Jason-1 GDR-B Results Cycles 1 to 185 Mean J-1 Bias: GDR-B Data: +107 mm Watson et al. Pg 8 of 11

7. Jan et al.

8. Mitchum et al.

9. Bosch et al.

10. Good performances of Jason-1 GDR data : 5.1 cm RMS at crossover, and stable Data performances better with GDR ‘B’: Variance gain = 21 cm²  35 % Conclusion 0 cm² 100 cm² SSH variance at crossovers using GDR “A” [cm²] • Some improvements will be provided in next GDR release : • New SSB (Labroue, Venice 2007) • JMR corrections • New Orbits • New geophysical corrections :DAC (MOG2D HR) 0 cm² 100 cm² Ablain et al. SSH variance at crossovers using GDR “B” [cm²]

11. 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 Ablain et al. 20cm² 0 cm²

12. Jason-1 and Envisat Mean Sea Level trends • Selection on Latitude (<66°), seasonal signals removed • Model wet tropo used Not consistent Consistent Not consistent • The EN and J1 MSL trend over the 4 years are not consistent • However the EN and J1 MSL trend are consistent over 2004-2005 period Envisat Jason-1 Faugere et al.

13. Summary • TMR recalibration is complete • TB drifts, gain and offset errors, and instrument temperature dependent errors were removed • PD coefficients were reverted to pre-launch values • TMR PDs are in good agreement with several validation sources • No drift compared to SSM/I • Low bias and negligible scale error compared to RaOb, GPS, and ECMWF • After JMR PD coefficient adjustment, TMR and JMR are in excellent agreement • Although, there is still room for regional improvement • JMR calibration will be updated on version-C GDRs Brown et al. Brown et al. OSTST07-Hobart

14. Recalibration of JMR • In preparation for Version C GDRs. • Will be ~3mm drier than version B GDRs. • Scale error corrected. • JMR-ECMWF drift reduced to –0.25 mm/yr • May have contribution from < 2 mm shifts after cycle 136 and 179 safeholds. • Will be corrected in Version C. Validation of JMRVersion B and Ongoing Recalibration • JMR from GDRB • All 4 comparisons agree to within 3.2 mm. • Residual (< 3mm) yaw state dependence may remain after cycle 100. • JMR-ECMWF has a drift of –0.3 mm/year. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session Desai et al.

15. 2 – Radiometer simulator Comparison between measures and simulations along track : • Validated for 2 different characteristic configurations • 2D maps are simulated: allow the evaluation in any possible configuration Obligis et al.

16. Tournadre et al.

17. Key points discussed • 1. What is best approach to aligning TOPEX and Jason for SSH time series? • Need integrated approach that reconciles global differences with results (coastal) at calibration sites. • Incumbent on Pis for cal sites to reconcile results/error budget for their (coastal) sites with expectations for global (open ocean) comparisons, e.g.: • - Use in-situ (GPS) model path delays • - Segregate results for low and high sea states (maybe regress against SWH, or eliminate low SWH overflight results) • - Use competing orbit products to develop empirical (site specific) corrections for geographically correlated orbit errors. • - Could be extended to other effects (e.g., waveform leakages on ALT-B) • Will the future new products (Retracked T/P GDR) and GDR-C answer to #1 question? Yes from global statistical approaches • Is there any improvement to be done before complete reprocessing? Some are under progress but inducing minor changes (e.g. JMR) • 4. Is it possible to give a unique error budget? Global? Geographic distribution? Coastal and or inland versus open ocean (radiometer land contamination)? • Priorities is to improve the correction for distance 50 to 250km • See #1; also, in-situ calibration sites are able to separate the origin of errors • 5. Need to identify/separate the constant and time varying parts of the errors • 6. Is Formation Flight (6 months) period sufficient or do we need to increase it for Jason-1 / Jason-2? • In balance with meso-scale studies. So 6 MONTHS IS ENOUGH • Implications of the change of orbits for Jason-3 on CALVAL activities? Needs to be evaluated in detail but keeping only one calibration site may not be reasonable. Moreover continuity is the cornerstone of the T/P Jason-1 missions