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Jason-1 / Envisat Cross-calibration

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

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Jason-1 / Envisat Cross-calibration

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

  2. 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

  3. More than 4 years available Data used GDR a GDR b Jason-1 Current processing 26 ............................................135 136………..178 Envisat Current processing 9 ................................................40 41 … 46 ..…52 • 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, …) • Updated correction on Jason-1: • Geophysical correctionsfor cycle <136 • SSB compatible with new standards for cycle >136 • Updated correction on Envisat: • Geophysical corrections for cycle <41 • USO drift + USO anomaly correction

  4. 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 SLA cycle 46 (cm) After correction Before correction 30 70 480 650 • A temporary correction is proposed by ESA: Auxiliary files are distributed for each products: FDGDR, IGDR, GDR.

  5. Envisat USO anomaly • 2 sets of USO correction are available for Ra-2 Envisat data: September 2005 February 2006 USO DRIFT only Has to be updated by the user USO DRIFT only Included in the product USO DRIFT + anomaly Has to be updated by the user More informations on http://earth.esa.int/pcs/envisat/ra2/auxdata/

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

  7. 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 3 -3 -3 3 (cm) (cm) • Reduction of the geographically correlated systematic differences • A residual East/West signal is noticed

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

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

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

  11. 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

  12. 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 http://www.aviso.oceanobs.com/html/donnees/calval/

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