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ENVISAT RA-2 L2 Products and Algorithms Verification Wind Wave Parameters

ENVISAT RA-2 L2 Products and Algorithms Verification Wind Wave Parameters. David Cotton, David Carter Satellite Observing Systems ESRIN March 2003. Data / Processing. FMAR, October - December 2002. from frap1.esrin.esa.it

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ENVISAT RA-2 L2 Products and Algorithms Verification Wind Wave Parameters

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  1. ENVISAT RA-2L2 Products and Algorithms VerificationWind Wave Parameters David Cotton, David Carter Satellite Observing Systems ESRIN March 2003

  2. Data / Processing • FMAR, October - December 2002. • from frap1.esrin.esa.it • GDR, October- December 2002 - ftp’d from fpac, converted to “GMAR” with Remko’s GDR2MAR • FD and GD data sets extracted into daily files with ESA SW (read_and_write_L2.f) • Flag testing routines commented out. • Subsequent processing with F77 / IDL /Matlab.

  3. SWH Distributions ENVISAT GDR SWH Ku October 2002 Envisat FMAR Ku ERS-2 FD ERS-2 OPR Envisat GDR / IMAR Ku ERS-2 OPR JASON IGDR TOPEX IGDR GFO IGDR

  4. Sigma-0 Distributions ENVISAT GDR s0 Ku October 2002 Envisat IMAR Ku ERS-2 OPR ERS-2 FD Envisat GDR Ku ERS-2 OPR JASON IGDR TOPEX IGDR GFO IGDR

  5. Wind Speed Distributions Envisat GDR ERS-2 FD JASON IGDR TOPEX IGDR GFO IGDR

  6. S - Band Distributions Envisat GDR Ku Band ENVISAT IMAR Ku Band ERS-2 FD ERS-2 OPR ENVISAT GDR S Band Envisat GDR Ku Band ENVISAT IMAR Ku Band ENVISAT GDR S Band

  7. Comments • Significant Wave Height (Ku) • Distribution matches other altimeters. • No low wave height cut-off (ERS2 FD). • Feature in FMAR at 0.5-0.8 m - fixed for GDR. • Ku Backscatter (s0) • FMAR/IMAR was ~ 3dB too low. • ENVISAT GDR now matches ERS-2 OPR. • Wind Speed • ENVISAT GDR distribution matches JASON / TOPEX • Extra values at ~0.05, 20

  8. SWH Regressions against Buoy Data ENVISAT GDR Ku v buoys Oct-Dec 02 ENVISAT FMAR Ku v buoys Oct-Dec 02 N=110 rrms 0.3086 m Grad = 0.9359 (± 3.5%) Intercept = 0.1752 (± 12 cm) N=56 rrms 0.3307 m Grad = 0.9475 (± 7.5%) Intercept = 0.1394 (± 22 cm)

  9. SWH Regressions against Buoy Data ENVISAT GDR S v buoys Oct-Dec 02 ENVISAT FMAR S v buoys Oct-Dec 02 N=95 rrms 0.6462 m Grad = 0.7739 (± 12 %) Intercept = 0.4545 (± 34 cm) N=54 rrms 0.5557 m Grad = 0.7875 (± 20%) Intercept = 0.3937 (± 55 cm)

  10. U10 Regressions against Buoy Data ENVISAT GDR v buoys Oct-Dec 02 ENVISAT FMAR v buoys Oct-Dec 02 N=110 rrms 1.4410 ms-1 Grad = 1.1408 (± 7 %) Intercept = -0.8677 ms-1(± 65 cms-1)

  11. FMAR / IMAR • In December we noted some inconsistencies between IMAR and FMAR - in setting of MCD flags, default values of Hs, U10 • Should be re-checked with FMAR/IMAR data from latest processing chains

  12. What mcd flags should be used? What ranges of hs, s0, U10 should be accepted? Can we use sd(H), sd(Hs), sd(s0), Nval (Hs), Nval(s0) Peakiness? Quality Criteria:Can we identify a set of criteria which will exclude “non-ocean” data?

  13. Data from 60°S to 60°N

  14. Some Hs = 0 and sd(Hs) .ne. 0. Extra occurrences at ws ~0.01, 20.0 ms-1. ws =20.0 an upper limit. Excluding sd(Hs) > 1.0, or sd(Hs) > 0.5 * Hs removes outliers, but excludes 20% of data. sd (range) could also be used - but more analysis required. What are suitable minimum limits for Nval? Observations

  15. Conclusion: • FMAR, IMAR: Most recent versions of FMAR, IMAR to be checked. • Hs • GDR Ku - slightly lower than NDBC buoys (~ 7% ± 3.5%) rrms 0.31m • FMAR Ku - cannot be distinguished from NDBC buoys , but error margins are higher than for GDR (±7.5%), rrms 0.33m • GDR S - significantly lower than NDBC buoys (~ 20% ± 12%) rrms 0.64m • FMAR S - similar to GDR S band Hs, ~20% lower than buoys. rrms 0.55m • s0 • GDR Ku mode close to that of ERS2 OPR • U10 • GDR distribution matches that of JASON-1, TOPEX/POSEIDON • GDR U10 > buoy U10, by ~ 14% (±7%) rrms 1.4 ms-1 • Extra values at ws~0.05, 20.0 ms-1 • Quality criteria • More analysis required.

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