New spectral estimate for SAR imaging of the ocean

Abstract

On the basis of the theory of microwave scattering from the ocean surface the correlation function of the synthetic aperture radar (SAR) signal intensity was obtained as a sum of two items. The first item is the proper image correlation function, i.e. the correlation function free of speckle noise SAR signal intensity, which has been investigated in many works (mostly by Alpers et al.). The second item describes the speckle structure in the image. It has been shown that at sufficiently large values of the well‐known velocity bunching parameter the speckle energy is significant within the spectral interval, where the spectrum of large ocean waves is concentrated. In this case the speckle noise can not be suppressed efficiently by means of image filtering. Meanwhile, the mentioned second item is nothing other than half of the correlation function of the complex intensity, which is the square of the SAR signal complex amplitude (unlike the usual real intensity, i.e. the square of the modulus). Therefore, the unspeckled image correlation function can be presented as the difference between the real intensity correlation function and half of the complex intensity function. This leads to a new spectral estimate, free of speckle noise, for the SAR image. The corresponding expression for the new estimate is presented.