Inherent error of Envisat ASAR level 2 algorithm and its correction

ESA's Envisat ASAR level 2 algorithm is used for retrieving ocean wave spectra (level 2 product) from synthetic aperture radar (SAR) single look complex (SLC) data. Our studies show that in addition to the contribution of wind wave part and swell part of the mixed waves, the cross spectra of mixed waves consist of an extra term. Just the extra term leads to an inherent error of this algorithm which has not been considered yet. This paper presents the error analysis of ESA's algorithm for ocean wave spectra retrieval in different significant wave height (SWH), wave length and wave component conditions based on simulation technique. To correct the inherent error of ESA's algorithm, a new method named unconstrained cross spectra method for directional ocean wave spectra retrieval from SAR SLC imagery is also presented. Case studies show that the new method can avoid the inherent error of ESA's algorithm very well.