Post on 21-Jan-2016
Jason-1/Envisat cross-calibration- 1 -
Y. Faugere (CLS)
J. Dorandeu (CLS)
N. Picot (CNES)
P. Femenias (ESA)
Jason-1 / Envisat Cross-calibration
Jason-1/Envisat cross-calibration- 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
Jason-1/Envisat cross-calibration- 3 -
EnvisatCurrent processing
Data used
9 ................................................40 41 … 46 ..…52
26 ............................................135 136………..178Jason-1Current 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 modelGeophysical corrections (MOG2D, tides, …)
GDR a GDR b• More than 4 years available
Updated correction on Jason-1:Geophysical corrections for cycle <136SSB compatible with new standards for cycle >136
Updated correction on Envisat:Geophysical corrections for cycle <41USO drift + USO anomaly correction
Jason-1/Envisat cross-calibration- 4 -
30 70480 650
Before correction After correctionSLA 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- 5 -
Envisat USO anomaly
February 2006
• 2 sets of USO correction are available for Ra-2 Envisat data:
September 2005
USO DRIFT onlyHas to be updated by
the user
USO DRIFT onlyIncluded in the
product
More informations on http://earth.esa.int/pcs/envisat/ra2/auxdata/
USO DRIFT + anomalyHas to be updated by the user
Jason-1/Envisat cross-calibration- 6 -
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 31-40
stdev 31-40
Mean 41-50
stdev 41-50
=>systematic differences
=>time varying differences
!
•Model wet tropo used
Jason-1/Envisat cross-calibration- 7 -
Performances at crossovers• EN/J1 10-day dual crossovers differences: systematic differences
-3 3 -3 3
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) (cm)• Reduction of the geographically correlated systematic differences • A residual East/West signal is noticed
Jason-1/Envisat cross-calibration- 8 -
0 3
• EN/J1 10-day dual crossovers differences: time varying differences
0 3(cm) (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- 9 -
Performances at crossovers
• Envisat and Jason-1 performances cross comparison at single 10-day crossover
Mean Standard 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- 10 -
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- 11 -
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 2004-2005 period
Selection on Latitude (<66°), seasonal signals removed Model wet tropo used
Jason-1
Envisat
Consistent Not consistentNot consistent
Jason-1/Envisat cross-calibration- 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/