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ENVISAT Ice Sheet Validation

ENVISAT Ice Sheet Validation

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ENVISAT Ice Sheet Validation

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  1. ENVISAT Ice Sheet Validation Anita C. Brenner1 H. Jay Zwally2 1Raytheon, ITSS 2NASA/Goddard Space Flight Center ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  2. ENVISAT Ice Sheet Data Validation • Range validity flags • Greenland and Antarctic Coverage and flag analysis • Geodetic correction comparison between ESA values on data and corrections calculated by NASA/GSFC algorithms • Retracking correction comparison between ice 2 and NASA/GSFC V4 models • Profile comparisons between ENVISAT and ERS-2 • Waveform comparions between ENVISAT and ERS-2 • Crossing Arc statistics for like and cross mission with ENVISAT and ERS-2 ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  3. Data Used • ENVISAT • 14 days of ENVISAT data covering October 4-17, 2002 from February 2003 release • Orbits as released on the data • ERS-2 • 14 days of coincident ERS-2 WAP products • DGME-04 orbits ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  4. Range Validity Flags • Ice 1 ranges marked valid for only a subset of ice sheet passes • No ice 2 ranges marked as valid over Greenland; only a subset of Antarctic passes are marked as having valid ice 2 ranges • Ocean ranges marked valid for ascending passes only ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  5. Valid sea ice ranges Valid Ice 1 ranges Valid ocean ranges Valid Ice 2 ranges ENVISAT measurements with range validity flags ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  6. Greenland Coverage ENVISAT Oct 4-17, 2002 320 Hz ERS-2 Oct, 2002 80 Hz 40 Hz ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  7. Greenland data • Majority of ENVISAT data in high resolution mode – smooth transition between modes allows for continuous coverage • ERS-2 data all in ice mode – spottier coverage along rougher areas • A large block of ascending ERS-2 passes were missing over Greenland – ocean portion of these passes exist ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  8. ENVISAT data over Greenland Fault and retracker flag idiosyncrasies – ice 2 range invalid all data WF Fault flag set Fault flag set, but NASA retracker successful Bad data determined by NASA retracker ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  9. ENVISAT Greenland data flagging inconsistencies • Over half of the data has the waveform fault flag set • Between 80 and 100 % of data with the waveform fault flag set for each pass was successfully retracked with NASA V4 algorithms • All ice 2 ranges were marked invalid – a large percentage of these looked good ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  10. Wf fault set and ice 1 Range marked as invalid Ice 2 range marked valid No flags checked Successfully Retracked with NASA algorithm Wf fault flag check and Edited by NASA retracker Antarctic ENVISAT Coverage and Flag Idiosyncrasies ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  11. ENVISAT Antarctic Data Flagging Inconsistencies • Large subset of passes had both the waveform fault flag set and ice 1 ranges marked invalid • Another subset of passes had ice 2 ranges marked invalid • The subsets mentioned above are mutually exclusive • NASA V4 retracker algorithm successfully processed most of the Antarctic Data no matter how the flags were set • Many of the ice1 and ice2 ranges flagged invalid were reasonable ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  12. Ice Sheet Geodetic Corrections • Ionosphere model correction missing on all ENVISAT data – used iri2001 model • Solid tide values agreed with those used by NASA/GSFC • Ocean tide values agreed well with NASA GOT99 model – some disagreements near coasts ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  13. Ice Sheet Geodetic Corrections (cont) • Dry troposphere correction agreed well over the oceans – up to 20 cm disagreement over land – GSFC model uses surface elevation from measurement – may be cause of disagreement • Wet troposphere correction agreed to within 1 cm ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  14. meters Comparison of Troposphere Delay corrections ESA vs NASA/GSFC Major difference is in Dry troposphere Correction over land meters meters meters meters ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  15. Comparison of Troposphere Delay corrections ESA vs NASA/GSFC Major difference is in Dry troposphere Correction over land ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  16. Comparison of Troposphere Delay corrections ESA vs NASA/GSFC ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  17. Profile Comparisons • Ice 2 range agrees well with NASA V4 retracked range over most portions of the ice sheet • ENVISAT/ERS-2 coincident profiles show same major features • ERS-2 elevations are noisier than ENVISAT elevations ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  18. Greenland elevation profile NASA V4 retracking correction – ice 2 100 meters -100 ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  19. ENVISAT and ERS-2 coincidentElevation profiles over Greenland ERS-2 ENVISAT ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  20. Greenland profile Blowup ERS-2 ENVISAT using ice 2 range ENVISAT using NASA retracking ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  21. Differences between Ice 2 and NASA V4 Retracking Ice 2 retracking NASA V4 retracking ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  22. Returns for Profile on Previous Slide ENVISAT – high resolution ERS-2 returns –coarse-ice mode ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  23. Retracking Algorithm results • Over majority of ice sheets the NASA V4 and ice 2 retrackers agree well • Ice 2 retracker sometimes picks locations before first ramp in the noise area • Ice 2 retracker sometimes misses first peak even when it is significant and picks a location farther down the return ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  24. Crossing Arc Analysis ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  25. 400 800 Sd=0.79m Mn=0.05m N=4515 Sd=0.40 Mn=0.00 N-4524 400 200 ESA cor/ ICE 1 retracker ESA cor/NASA retracker -4 -4 -4 -4 -2 -2 0 0 2 2 4 4 -4 -2 -2 -2 0 0 0 2 2 2 4 4 4 800 400 500 Sd=.74m Mn=0.03m N=4505 Sd=0.39m Mn=0.00m N=4515 Sd=0.47m Mn=0.01m N=4244 300 400 200 100 NASA cor/ice 2 retracker NASA cor/NASA retracker NASA Cor/ ICE 1 retracker ENVISAT Antarctic Crossing Arc Statistics – different retrackers and geodetic corrections – iri 2001 ionosphere model used for all ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  26. ENVISAT Crossing Arc Precision over Antarctica centimeters Iri 2001 Ionosphere Model for all ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  27. Like Mission Crossing Arc Statistics Over Antarctica centimeters Greenland ODR orbits for ERS-2 Original orbits for ENVISAT ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  28. Antarctica Greenland Cross-Mission Crossover Statistics ERS-2-ENVISAT over Antarctica 150 100 50 0 Mean Sd -50 -100 -150 NASA retracker and Geodetic corrections ENVISAT – orig orbits ERS-2 – ODR orbits ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting

  29. Crossing Arc Analysis Summary • Lowest statistics achieved with ice 1 range using NASA geodetic corrections • NASA geodetic corrections reduced standard deviation of crossover residuals by 4 cm • ENVISAT precision similar to that of Geosat/Seasat since in fine mode • ENVISAT/ERS-2 crossovers show ENVISAT higher by a mean of 1.18m over Greenland and 1.34 m over Antarctica ENVISAT RA-2/MWR CCVT Sixth Plenary Meeting