A significant wave height retrieval algorithm from complex synthetic aperture radar (SAR) data without prior information is presented. The semi-empirical model is derived based on theoretical SAR imaging mechanism of ocean wave and the empirical relation between two types of wave period. A preliminary validation using the Envisat ASAR wave mode data shows a good result compared with the collocated buoy data from NDBC. The bias and RMS respect to the in situ measurements are −0.11m and 0.64m. It is shown that, for Envisat ASAR data, this method works well.
Significant wave height (SWH) is one of the most important parameters of ocean surface wave for offshore engineering. Nowadays, due to its high spatial resolution, wide coverage and independence of weather conditions, spaceborne Synthetic Aperture Radar (SAR) has become a powerful tool for providing valuable information on SWH (Krogstad and Barstow, 1999). Traditionally, SWH is derived from SAR imagery by integrating the directional ocean wave spectrum retrieved in advance. Although various retrieval algorithms have been developed, there are some disadvantages with these inversion schemes. First, the results depend on a first-guess wave spectrum or additional wind information, through the integration of wave spectrum retrieved with MPI (Hasselmann and Hasselmann, 1991; Hasselmann et al., 1996), SPAR (Mastenbroek and de Valk, 2000) or PARSA (Schulz-Stellenfleth et al., 2005) algorithm. Second, other algorithms, such as ESA's level 2 algorithm (Johnsen et al., 2002) and Lyzenga's unconstrained algorithm (Lyzenga, 2002), may underestimate the SWH due to the lack of spectral information beyond a high wave number cutoff. Recently, Schulz-Stellenfleth et al. (2007) put forward an empirical algorithm for ERS wave mode data named CWAVE, which can derive SWH of ocean waves including wind waves without prior knowledge of wind or wave information.
