SAR OCEAN WAVE INVERSION USING IMAGE CROSS SPECTRA

Image cross-spectra obtained by combining pairs of single look SAR ima ges are utilized in an inversion scheme for extracting the underlying ocean wave spectrum. The reasons for proposing the use of image cross- spectra instead of standard multilook spectra are twofold, First, the image cross-spectra are shown to significantly reduce the speckle nois e level while preserving the spectral shape, Second, the image cross-s pectra provide information about the wave propagation direction. A clo sed form expression of the ocean-to-SAR spectral transform and its inv ersion is formulated for the cross-spectral case, The inversion method is based on computing the full derivative of the nonlinear ocean-to-S AR image cross-spectral transform. The SAR image cross-spectra are sho wn to yield a SNR typically 16-25 dB higher than the corresponding sta ndard 3 look image spectra, The noise level is typically reduced with a factor of 20 compared to the 3 look spectra and a factor of 60 compa red to the single look spectra. The inherent information about the wav e propagation direction is utilized in the inversion scheme to resolve the 180-degree ambiguity without using any external information, The method is demonstrated on airborne C-band SAR data.