Retrieval of ocean wave spectra and RAR MTF's from dual-polarization SAR data

A method for the retrieval of the real aperture radar (RAR) modulation transfer function (MTF) and ocean wave spectra from dual-polarization (i.e., simultaneously acquired HH and VV polarizations) synthetic aperture radar (SAR) image data is described. The RAR MTF is estimated by applying empirical MTF estimation methodologies to inter-look cross spectra between various combinations of individual looks and available polarizations for a given radar frequency. The concept behind the nonlinear inversion is that any combination of like- and cross-polarization image spectra should return the same wave spectrum, in agreement with in situ and model wave spectra. This permits estimation of the RAR MTF on a case-by-case basis. The results are compared with theoretical treatments of the RAR MTF, which are shown to be inadequate for the range of conditions encountered in their data set. However, the theory and measurements fit well in describing the polarization dependence of the RAR MTF. The data set consists of SIR-C/X-SAR L-band and CCRS CV-580 C-band SAR data, in situ buoy measurements, and model data from field programs in Canadian waters in October and December 1994.