NON-GAUSSIAN SIGNAL, STATISTICS IN OCEAN SAR IMAGERY

In this paper, we have studied the significance of non-Gaussian signal statistics in some synthetic aperture radar (SAR) images of the ocean surface, The study consisted of calculating the amplitude histogram o f the returned echoes from the images and comparing these with the Ray leigh- and K-v-distributions, corresponding to the Gaussian and non-Ga ussian statistics, respectively. The images used were some C-band SAR data from the Canadian airborne SAR collected during the NORCSEX'88 ca mpaign and some ERS-1 data collected during the NORCSEX'91 campaign, T he analysis of the NORCSEX'88 data included studies of the dependency of the signal statistics on incidence angle and meteorological and ima ging conditions, It was found, specifically at small incidence angles, that there was a significant deviation from Gaussian statistics, It w as also found that when the wind was blowing against the wares, the de viation from Gaussian statistics was more pronounced than when the win d was blowing in the same direction as the waves were propagating, The study also showed a correlation between the signal statistics and the width of the SAR image spectra, At low incidence angles, this agrees with the interpretation that non-Gaussian statistics may be related to strong widebanded scattering events, However, since non-Gaussian stat istics also were observed at incidence angles as high as 50 degrees, i t is evident that the modulation of the scattering cross section by th e long waves is also an important factor, In addition, the analysis of the ERS-1 data shelved that to account for the width of the SAR image spectra, an azimuth smearing term, due to short scene coherence time, had to be included, This was in the present work done by modeling the short-coherence-time-smearing as a Gaussian low-pass filter, By this procedure, we were able to obtain realistic estimates for the average scene coherence time of the SAR scenes.