Application of wave spectra retrieved from ERS-1 SAR wave mode spectra in a wind- and wave-data assimilation system

An improvement of an earlier algorithm for retrieving ocean wave spectra from SAR image spectra is presented. The scheme uses a modified cost function and an additional iteration loop. A spectral partitioning scheme decomposes the spectrum into a finite number of wave systems. At each iteration step the individual wave systems of the first guess spectrum are modified to agree in mean wave height, mean wave frequency and direction with the corresponding values of the SAR-inverted wave spectrum, thus yielding a new first guess for a new iteration, if necessary. The algorithm retrieves smooth wave spectra and in addition provides consistent spectral partitioning parameters which can be used in combined wind-and-wave data assimilation. Two assimilation schemes are presented: an optimal interpolation scheme which uses the first guess and SAR-retrieved characteristic parameter as input data and a Green´s function approach which inverts the differential operator of the wave transport equation. The schemes are applied to the ERS-1 SAR data for the Atlantic Ocean and the resulting local wind corrections are intercompared