Statistical Analysis and Intercomparison of Global Ers-1 Sar Wave Mode Spectral Retrievals Using Wam Model and Buoy Data

SPECTRAL RETRIEVALS USING WAM MODEL AND BUOY DATA P. Heimbach, S. Hasselmann, K. Hasselmann and M. Toporek Max-Planck-Institut f ur Meteorologie, Bundesstra e 55, D-20146 Hamburg, Germany Phon: + 49 / 40 / 4 11 73 3 77, Facs: + 49 / 40 / 4 11 73 2 98 E-mail: [email protected] Abstract A global statistical intercomparison was carried out for the period January 1993 to December 1995 between wave spectra retrieved from ERS-1 SAR Wave Mode (SWM) data using an inversion algorithm of the closed nonlinear wave-to-SAR spectral mapping relation and wave spectra computed with the wave model WAM. A combined quality analysis of the satellite data and a performance analysis of the retrieval algorithm was performed. The assessment yielded about 75 percent successful retrievals. The histogram of pattern correlation between best estimate and observed SAR spectra is sharply peaked at 0.9. The retrieval was repeated using 1,000 collocated buoy spectra as rst guess. Both retrievals agreed very closely in terms of the mean spectral parameters, con rming that the retrieval is independent of the rst guess. The azimuthal cut-o wavenumber, a measure of the rms orbital velocity, was investigated. Despite the limited resolution in azimuth due to this cut-o , about 75 % of the swell is explicitly resolved by the SAR, proving its general ability to detect a signi cant part of the ocean wave eld. Comparing the cut-o wavenumber to the wind speed no simple relationship between both quantities could be found, as additional e ects such as wave age or fetch were not taken into account.