A nonlinear mapping from dual−polarization SAR image spectra to Ocean wave spectra

It is well known that ocean waves are an important component of upper ocean dynamics. The synthetic aperture radar (SAR) has been widely used to measure ocean surface wave spectra from space since the Seasat satellite was launched in 1978. Many papers have been published dealing with the imaging mechanism and retrieval methodology. Schuler and Lee proposed a method to improve the measurement of directional ocean wave spectra based on the identification of a new modulation process, polarization orientation modulation. We derived the polarization orientation modulation transfer function and tilt modulation transfer function of a linear polarization SAR. The ocean surface wave spectra are retrieved by using an image intensity−based algorithm. Recently, a new method was proposed by Lee et al., and independently by Pottier, that measured azimuth components of ocean wave slopes and wave spectra using the relationship between polarimetric orientation angle shift and the azimuth surface tilts. The key to this method is estimation of the orientation angles. Here, we present a new method to measure ocean wave slopes in the range direction using dual−polarization Real Aperture Radar (RAR) image intensity, without need for estimation of the polarization orientation angles. In the velocity bunching model, a nonlinear mapping relationship between dual−polarization SAR image spectra and Ocean wave spectra is derived and the uncertain hydro−dynamical modulation function is not included. Some numerical simulation test has done. Comparisons will be made between ocean wave spectra measured using ENVISAT C band dual−polarization (HH and VV) backscatter data and in situ buoys.