Jason-1/Envisat cross-calibration Y. Faugere (CLS) J. Dorandeu (CLS) N. Picot (CNES) P. Femenias (ESA) Jason-1 / Envisat Cross-calibration

Jason-1/Envisat cross-calibration Introduction Objective: to show the improvement of the consistency between Jason-1 and Envisat in the GDRb configuration Data used Envisat USO anomaly Performances at crossovers Mean Sea Level trends Conclusion

Jason-1/Envisat cross-calibration Envisat Current processing Data used … 46..… ………..178 Jason-1 Current processing Main Jason-1 GDR b changes:  New orbit configuration (EIGEN-CG03C)  New retracking (MLE4)  Geophysical corrections (MOG2D, tides, …) Main Envisat GDR b changes:  New orbit configuration (EIGEN-CG03C)  New wind speed model + new SSB model  Geophysical corrections (MOG2D, tides, …) GDR aGDR b More than 4 years available Updated correction on Jason-1:  Geophysical corrections for cycle <136  SSB compatible with new standards for cycle >136 Updated correction on Envisat:  Geophysical corrections for cycle <41  USO drift + USO anomaly correction

Jason-1/Envisat cross-calibration Before correction After correction SLA cycle 46 (cm) Envisat USO anomaly Since February 2006, Envisat Ra-2 data have been affected by a major anomaly: the Ultra Stable Oscillator (USO) anomaly The anomaly consists in a a change of frequency of the USO device: bias + oscillating signal at the orbital period Translated into range, the impact is a ~5.5m bias + 30 cm of amplitude orbital signal A temporary correction is proposed by ESA: Auxiliary files are distributed for each products: FDGDR, IGDR, GDR.

Jason-1/Envisat cross-calibration Envisat USO anomaly February sets of USO correction are available for Ra-2 Envisat data: September 2005 USO DRIFT only Has to be updated by the user USO DRIFT only Included in the product More informations on USO DRIFT + anomaly Has to be updated by the user

Jason-1/Envisat cross-calibration Performances at crossovers EN/J1 10-day dual crossovers differences: methodology grid cycle 31 grid cycle 32. grid cycle 40 Cyclic mean differences in 2°x2° boxes year 2005 Cyclic mean differences in 2°x2° boxes year 2006 grid cycle 41 grid cycle 42. grid cycle 50 Mean stdev Mean stdev =>systematic differences =>time varying differences ! Model wet tropo used

Jason-1/Envisat cross-calibration Performances at crossovers EN/J1 10-day dual crossovers differences: systematic differences EN-J1 mean (cycles 31-40) GDR A products EN-J1 mean (cycles 41-50) GDR B products + SSB compatible with the new standards (cm) Reduction of the geographically correlated systematic differences A residual East/West signal is noticed

Jason-1/Envisat cross-calibration EN/J1 10-day dual crossovers differences: time varying differences 0 3 (cm) Strong reduction of the time varying differences residual signal in North-West Atlantic, Indonesia EN-J1 stdev (cycles 31-40) GDR A products EN-J1 stdev (cycles 41-50) GDR B products + SSB compatible with the new standards Performances at crossovers

Jason-1/Envisat cross-calibration Performances at crossovers Envisat and Jason-1 performances cross comparison at single 10-day crossover MeanStandard deviation Similar performances for the two missions  Selection on Latitude (<50°) bathymetry (<-1000 m) variability (<20cm) Annual signal on Envisat February 2006

Jason-1/Envisat cross-calibration Jason-1 and Envisat Mean Sea Level trends The EN and J1 MSL trend over the 4 years are not consistent Jason-1 Envisat  Selection on latitude (<66°), seasonal signals removed  Model wet tropo used

Jason-1/Envisat cross-calibration Jason-1 and Envisat Mean Sea Level trends The EN and J1 MSL trend over the 4 years are not consistent However the EN and J1 MSL trend are consistent over period  Selection on Latitude (<66°), seasonal signals removed  Model wet tropo used Jason-1 Envisat Consistent Not consistent

Jason-1/Envisat cross-calibration Conclusion The geographical differences between Envisat and jason-1 are strongly reduced by: –the new geophysical corrections, –the use of Grace gravity fields in the orbit calculation –A new Jason-1 SSB compatible with the new standards (not in the product yet). Slight geographically correlated errors still remain. Longer time series in the new version are needed for fine investigation of the residual differences The performances of both Jason-1 and Envisat are good and similar. The USO anomaly correction allows Envisat Ra-2 data to recover their nominal quality The Envisat Mean Sea Level is inconsistent with the other altimeters at global and local scale. Cross-calibration against EnviSat is crucial: –For the Jason-1 performance assessment: In the context of only two precise altimeter missions flying together (T/P is no more there!) –For preparing the Jason-2 launch: 3rd point of comparison to secure the cross-calibration exercise –Also requires further efforts on EnviSat long term performance (stability) More results:  Poster  Cyclic and yearly reports