An Empirical Approach for the Retrieval of Integral Ocean Wave Parameters from Synthetic Aperture Radar Data

Abstract

In this study a new empirical approach to retrieve integral 1 ocean wave parameters from synthetic aperture radar (SAR) data is presented. The idea behind this computationally e_cient technique is to estimate integral ocean wave parameters without the intermediate step of retrieving the 2-D ocean wave spectrum. The method has the radiometrically calibrated SAR image as the only source of information and is based on a quadratic model function with 22 input parameters. These parameters include the radar cross section, the image variance and 20 parameters computed from the SAR im age variance spectrum using a set of orthonormal functions. The coe_cients of the quadratic function were _tted for the estimation of Hs, the mean peri ods Tm01; Tm02; T􀀀10, the wave power and the wave heights associated with di_erent spectral bands. The _t procedure is based on a stepwise regression method. A data set of 12000 globally distributed ERS-2 wave mode image spectra and co-located WAM ocean wave spectra was available for the study. Two separate subsets of 6000 collocation pairs each were used to _t the model and to carry out comparisons of the retrieved wave parameters with numerical model results. Additional comparisons were performed using NDBC buoy measurements. Scatter plots and global maps with the derived parameters are presented. It is shown that the rms of the SAR derived Hs with respect to the WAM Hs is about 0.5 m. For the mean period Tm􀀀10 an rms of 0.72 s with a high frequency cuto_ period of about 6 s is achieved.