A semiempirical algorithm for SAR wave height retrieval and its validation using Envisat ASAR wave mode data

Many synthetic aperture radar (SAR) wave height retrieval algorithms have been developed. However, the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted to the long wave regime. A semiempirical algorithm is presented, which has the objective to estimate the wave height from SAR imagery without any prior knowledge. The proposed novel algorithm was developed based on the theoretical SAR ocean wave imaging mechanism and the empirical relation between two types of wave period. The dependency of the proposed model on radar incident and wave direction was analyzed. For Envisat advanced synthetic aperture radar (ASAR) wave mode data, the model can be reduced to the simple form with two input parameters, i.e., the cutoff wavelength and peak wavelength of ocean wave, which can be retrieved from SAR imagery without any prior knowledge of wind or wave. Using Envisat ASAR wave mode data and the collocated buoy measurements from NDBC, the semiempirical algorithm is validated and compared with the Envisat ASAR level 2 products. The root-mean-square-error (RMSE) and scatter index (SI) in respect to the in situ measurements are 0.52 m and 19% respectively. Validation results indicate that, for Envisat ASAR wave mode data, the proposed method works well.