G. Engen et H. Johnsen, SAR OCEAN WAVE INVERSION USING IMAGE CROSS SPECTRA, IEEE transactions on geoscience and remote sensing, 33(4), 1995, pp. 1047-1056
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.