Azimuth Smearing in Ocean-Sar Image Spectra: A Study of Hasselmann's Closed-Form Transformation Based on Simulations of Norcsex' 88 Sar Data

The well known along track resolution loss in S A R ocean wave image specIra is investigated comparing simulations based on Hasselmann's nonlinear integral nansform and measurements from the NORCSEXS8 experiment. In the literature, the resolution loss has often been modeled as a lowpass fdter process, described by the rms azimuth shift width ox, acting within a quasilinear S A R transformation. Estimates from real data of ox, as a function of the range-to-platform velocity (R/V) and incidence angle, are compared to Hasselmann's new nonlinear spectral transformation and the widely used quasilinear model. Simulations correlated with real wave data show that the quasilinear model, with this dataset and with contributions to ox from the entire spectrum, overestimates ox with roughly 3040%. The conformity between Hasselmann's model and real data is however excellent. The numerics also indicate that the nonlinearity degree in Hasselmann's transform is explicitly related to the surface truth parameters significant waveheight and peak wavelength whcreas thc spectral bandwidth, including thc subresolution part of the Ocean wave spectrum, seems to be of minor importance. It is also shown that the resultant smearing can not (due to imaging nonlinearities) explicitly be separated from the coherent linear velocity bunching part of the transform.