VALIDATION OF THE ASAR WAVE MODE LEVEL 2 PRODUCT USING WAMAND BUOY SPECTRA

摘要

More than 70 thousands of ASAR Wave Mode Level 2rnproducts are validated globally using co-locatedrnECMWF WAM spectra and wind speed data. A largernnumber of co-located ASAR, WAM and buoy spectrarnare also used in the validation. The data used in thernvalidation covers all ASAR Wave Mode acquisitions inrnthe period April and March 2003. Globally, therngeophysical validation of wind and wave parametersrnshow reasonably agreement for the mean wave period,rnsignificant waveheight and mean wave direction,rnespecially for the long wavelength part of the spectra.rnHowever, for certain coastal and sheltered areas largerrndeviations are observed, probably due to fetchrnlimitations and/or impact of other coastal surfacernfeatures on the SAR signature. On average the ASARrntends to measure a slightly longer mean swell periodrn(≈0.8s)than predicted by WAM. ComparingrnASAR, WAM and buoy spectra, examples are shownrnwhere ASAR consistently adds information on thernswell systems beyond what is predicted by WAM. Forrnthe ASAR Level2 significant waveheight, saturationrneffects at high sea-states are observed, increasing withrnincreasing wind speed. Less saturation is observed forrnthe long wavelength part of the spectrum. Thernsaturation is mostly due to the well-known effect ofrnazimuth cut-off, which increases with increasing searnstate. At low wind speed an overestimation ofrnwaveheight is observed compared to WAM. This isrncaused by the use of CMOD-IF2 based MTF [5] whichrnunderestimates the backscatter modulation at low windrnspeed as compared to SAR due to the high spatialrnvariability of SAR cross section at low wind speeds.rnStatistics and global maps comparison are alsornpresented, showing the capabilities of ASAR WavernMode to provide global coverage of wave spectralrnparameters.