He. Krogstad et al., GENERALIZATIONS OF THE NONLINEAR OCEAN-SAR TRANSFORM AND A SIMPLIFIEDSAR INVERSION ALGORITHM, Atmosphere-ocean, 32(1), 1994, pp. 61-82
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.