GENERALIZATIONS OF THE NONLINEAR OCEAN-SAR TRANSFORM AND A SIMPLIFIEDSAR INVERSION ALGORITHM

It is demonstrated that the non-linear transform from the ocean wave s pectrum to the synthetic aperture radar (SAR) image spectrum may be ex tended to include point target spreading (dispersive) effects. For pra ctical purposes, the extension amounts to an additional azimuth spectr al cut-off factor applied to the result of the velocity bunching non-l inear transform without point-target dispersion. The validity of a qua si-linear approximation is analysed by means of simple Gaussian test s pectra, which also reveal the nature of the fully non-linear velocity bunching transform. The inversion problem is formulated as a constrain ed functional minimization over non-negative wave spectra. An iterativ e solution method that requires an a priori estimate of the wave spect rum is demonstrated Analysis of the method leads to a simple theory fo r preparing the necessary weight functions for the observed SAR and th e a priori wave spectra. Combined with an optimized quasi-linear ocean -SAR transform, the new formulation leads to a very simple and efficie nt SAR inversion.