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Envisat Range Cross-Calibration in the Mediterranean Sea

Envisat Range Cross-Calibration in the Mediterranean Sea. Luciana Fenoglio-Marc, Institute of Physical Geodesy, Darmstadt Technical University ENVISAT RA-2/MWR CCVT sixth Plenary Meeting, 25-27 March 2003, ESA/ESRIN. (0.0). 1) Data 2) Corrections

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Envisat Range Cross-Calibration in the Mediterranean Sea

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  1. Envisat Range Cross-Calibration in the Mediterranean Sea Luciana Fenoglio-Marc, Institute of Physical Geodesy, Darmstadt Technical University ENVISAT RA-2/MWR CCVT sixth Plenary Meeting, 25-27 March 2003, ESA/ESRIN

  2. (0.0) 1) Data 2) Corrections 3) Dual crossovers between Envisat and ERS-2, Topex, Jason 4) Comparison of ssh with Mean Sea Surface model 5) Colinear analysis of Envisat and ERS-2 6) Conclusions

  3. (1.0) DATA Data used Table 1

  4. (2.0) CORRECTIONS Table 2. Corrections used in DXO and Colinear Analysis Original suggestion to CCVT: ocean tide GOT99.2 and load tide FES99. Our suggestion: use same model for ocean and load tide model, e.g. GOT00.2.

  5. (3.0) RANGE BIAS ESTIMATION : DUAL CROSSOVERS Estimation of range bias from dual crossovers Table 3 1) Improvement by scaled wet tropo? The rms improvement is small and the mean changes by 5.3 mm 2) The mean dual crossover difference has changed wrt value obtained from GDR distributed in Nov.-Dec. 2002

  6. (3.1) RANGE BIAS ESTIMATION : DUAL CROSSOVERS (17.5 day constraint) Envisat (10-12) – ERS-2 (78-80) Envisat (10-12) – Topex (69-75) Envisat (10-12) – Jason (27-42) Figure 1

  7. (4.0) RANGE BIAS ESTIMATION : Comparison with MEAN SEA LEVEL Table 4. Height above the MSS

  8. (5.0) RANGE BIAS ESTIMATION : Colinear analysis Colinear analysis: ssh differences (6 corrections are not applied) Figure 2 1) descending passes higher than ascending passes. Is there a time bias? 2) mean ssh difference has changed wrt value from December data

  9. (5.1) RANGE BIAS ESTIMATION : Colinear analysis ssh differences (5 corrections are not applied, Delta SSB is applied) 1) no significant changes wrt to use of BM3/BM4 SSB model Figure 3 • Not significant difference wrt Figure 1 • As in Figure 2 descending passes higher than ascending passes.

  10. (5.2) COMPARISON of SWH: Colinear analysis Figure 4 Do Envisat and ERS-2 observe the same SWH ?

  11. (5.3) COMPARISON of SWH: Colinear analysis Colinear analysis : SWH differences Figure 5 Mean = 20.36 cm STD = 29.46 cm Nr of points =10671

  12. (5.4) COMPARISON of WIND SPEED: Colinear analysis Colinear analysis: Wind speed differences Figure 6 Envisat and ERS-2 observe the same Wind Speed 

  13. (5.5) COMPARISON of WIND SPEED: Colinear analysis Figure 7 Mean = 0.08 m/s STD = 0.64 m/s Nr of points =10671

  14. Conclusions 1) Dual crossovers give the range bias of Envisat relative to ERS-2 (112.3 +/ 9.2 cm), Topex (118.8 +/- 8.5 cm) and Jason (108.7 +/- 8.2 cm) (10 days DXO constraint) 2) Colinear analysis with ERS-2 shows differences at around 110 cm 3) The range bias between Envisat and ERS-2 is about 70 cm higher than the previous estimation. Reason for the change is unknown. 4) Possible problems in the data have been identified in the colinear analysis (timing biases, SWH differences not equal to zero) 5) Alternative and improved corrections (Delta SBB) and correction to existing models (factor for dry tropo) have been tested and produce small changes in the results. 6) The choice of best set of corrections is still under investigation 7) Test in a small area: advantages (small set) and disadvantages (peculiar characteristics, e.g. Mediterranean is a low-SWH area). Agreement with global results is expected.

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