I. Introduction
It is taken for granted that satellite-borne synthetic aperture radars (SAR) are able to provide directional wave information on a global scale. The retrieval of the wave spectrum from SAR complex images is based on the inversion of Hasselmann's integral transform [9], [16], [5], which maps the ocean wave number spectrum to the SAR image variance cross-spectrum. Still, the understanding of the real aperture radar (RAR) modulation transfer function (MTF) remains a key issue [6]. This function, which describes the modulation of the radar backscatter by the long waves, depends on the local wind conditions, the wave/wind imaging geometry as well as the radar frequency and polarization. Its contribution to the SAR imaging process becomes crucial for ocean waves that travel parallel to the range axis, and for instance, the same long waves may be imaged in very different manners by the SAR according to the local wind conditions [12].