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Isotropic and Anisotropic FEXP-Fractal Spectral Models for High Resolution Sea SAR Images

The aim of this paper is the definition of an anisotropic self-similar spectral model for high-resolution sea synthetic aperture radar (SAR) imagery. The assumption of spatial isotropy for sea SAR images is valid when the sea is calm, as the sea wave energy is spread in all directions and the SAR image PSD shows a circular symmetry. However, if the surface wind speed exceeds 7 m/s the anisotropy of sea SAR images starts to be perceptible. In this work we define an anisotropic spectral model by adding a 2-D isotropic fractionally exponential model (FEXP) to an anisotropic term defined starting from the fractal model of sea surface spectra. For this FEXP-Fractal (FEXPF) model we define a new class of spreading functions to characterize the anisotropic component. FEXPF models allow the spectra of sea SAR images to be simulated in different sea states and wind conditions - and with oil slicks -at low computational costs. FEXPF demonstrated reliable results when applied to European Remote Sensing (ERS) SAR Precision Images (PRI) of the Mediterranean Sea and the AtlanticOcean.