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ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker

Validation and tuning of the Ice2 retracking algorithm. B. LEGRESY, F. REMY, F. PAPA, G. VINAY , M. VAN DEN BOSSCHE and O.Z. ZANIFE. LEGOS CLS. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker.

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ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker

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  1. Validation and tuning of the Ice2 retracking algorithm B. LEGRESY, F. REMY, F. PAPA, G. VINAY , M. VAN DEN BOSSCHE and O.Z. ZANIFE LEGOS CLS ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker The Ice2 retracker consist in detecting the waveform edge, fitting an erf to the leading edge and an exponential to the trail. The main outputs are : Leading edge amplitude (ice2LeBs (0.01dB)) Range (ice2Range (mm)) Leading edge width (ice2edgewidth (mm)) Trailing edge slope (ice2FirstPartofTE (s-1)) Backscatter(ice2Bs (0.01 dB)) All parameters output in both Ku and S band B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 Rémy & al. 1996, Legrésy and Rémy, 1997 …

  2. Validation and tuning of the Ice2 retracking algorithm B. LEGRESY, F. REMY, F. PAPA, G. VINAY , M. VAN DEN BOSSCHE and O.Z. ZANIFE LEGOS CLS ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker • 1) Preliminary check of data • - One track segment of data (5th of july) had been analysed in august • - Another segment had been scanned by end of october • 2) Extensive check of data • Part of cycle 10 has been available at the same time as for CCVT and analysed by end november, beginning of december • - Mid december – mid january several tracks had been available at both • L1b and L2. B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  3. Major findings The algorithm performs quite well when the edge detection is performing OK. 1) A major problem arises on wave front detection. It had been identified and reported at the first segment analysed and a preliminary solution been brought by tuning the algorithm parameters (thermal noise detection ratio…) but needed a consequent amount of data to be analysed in order to conclude on the need to improve the detection algorithm. The first amount of cycle 10 data proved the tuning coefficient was insufficient and the need for a more robust detection scheme. This scheme has been proposed at mid december and tests in december-january and proved its robustness. It has been successfully implemented on the near real time processor. It is under implementation on the ground segment (CMA). Not included in the current GDR. See Milagro & al. 2003 for a more detailed description. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  4. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 With bad detection (what you have in hand) With better detection (what you’ll have) The detection frequently occur in the noise leading to a very low amplitude and bad parameters recovery and frequently no detection at all.

  5. 2) A minor problem had been found in the sampling algorithm of the least square scanning. This problem results in an additional small scale noise (up to 30 cm R.M.S. at 20 km scale). It has been successfully corrected on the near real time processor. It is under implementation on the ground segment (CMA). 3) Cross validation with the ocean retracker over ocean surfaces revealed that, when the wave front detection works OK, Ice2 retracking process the data correctly and all the output value are within acceptable ranges. 4) Cross validation with the ERS outputs (processed with a former version of the Ice2) proved the parameters values are in very good accordance even if non contemporary. 5) Editing the GDR (CMA) with criteria eliminating most of the badly detected data conserves a sufficient amount of data to validate maps of the Ice2 output parameters : For the first time we can easily observe the continental surfaces with level 2 radar altimeter data in both Ku and S band (new). ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  6. Height maps (in m) in both bands (Ku) at left, (S) at right, (Ku-S) below. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  7. Backscatter maps (in dB) in both bands (Ku) at left, (S) at right, (S-Ku) below. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  8. Leading edge maps (in 1/10m) in both bands (Ku) at left, (S) at right, (Ku-S) below. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  9. Trailing edge maps (in 1000s-1) in both bands (Ku) at left, (S) at right, (Ku-S) below. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  10. Validation by comparing with TOPEX Backscatter diff (C-Ku)/(S-Ku)in dB 9 years average of november TOPEX (s0C-s0Ku) (Papa & al. 2002 ; 2003) observations compare well with the data available on cycle 11 for ENVISAT(s0S-s0Ku).ENVISAT provide more resolution in space and more dynamic resolution in backscatter => better recovery of vegetation / snow... ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 ENVISAT (S-Ku) Backscatter

  11. ENVISAT also extend to the polar regions ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 There is a fairly good agreement with height measured by ERS (Rémy & al. 1999) ~ 50cm RMS, all corrections not yet applied

  12. Extension to the polar regions : Comparison with ERS Backscatter in Ku ENVISAT ERS ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 The same Ku band backscatter as ERS pattern is observed (Legresy &Remy, 1997)

  13. Extension to the polar regions : Comparison with ERS Leading edge in Ku ENVISAT ERS ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

  14. Extension to the polar regions : Dual frequency promising ENVISAT ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker ERS Ku 11m height difference! Very deep penetration? B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002 The difference in parameters behaviour with frequency show strong variations in space and promise to help describe the snowpack directly while it was necessary to use the temporal variability to recover relevent parameters with ERS (Legresy & Remy, 1998).

  15. CONCLUSION For the first time we can easily observe the continents with level 2 radar altimeter data in both Ku and S band altimetry. Only one major problem has been identified in the L2 processing chain for Ice2, it has been solved and is corrected. As far as a large editing is performed, the first output data validate well the algorithm. The new dual (Ku/S band) allied to the Ice 2 outputs represent a powerful tool for new insights in continental surface studies. ESA-ESRIN ENVISAT-CCVT. Ice 2 retracker B. LEGRESY (CNRS/LEGOS) & al., ESL RA2MWR CLS-LEGOS 24 March 2002

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