Simulation studies of SAR remote sensing of doubly peaked ocean waves

Two kinds of doubly peaked ocean wave spectra such as Torsethaugen spectrum and Ochi-Hubble spectrum are used to simulate the mixed ocean waves with both swells and wind seas. The Envisat ASAR (Advanced Synthetic Aperture radar) image cross spectra of mixed ocean waves in different significant wave height (SWH), wave direction, wave component and peak period are then simulated by using Engen's nonlinear transformation formula. Analysis based on the simulation indicate that (1) in addition to the contribution of wind wave part and swell part of the mixed waves, the cross spectra of mixed waves consist of an extra term; (2) the cross spectra of mixed ocean waves dilate in range direction and shrink in azimuth direction (the so-called azimuth cutoff effect) and the cutoff effect increases for waves with larger wave height, or for waves propagating closer the azimuth direction, or for waves containing more wind wave component, or for waves with shorter peak period; (3) the cross spectra split into two parts for waves propagating along range direction; (4) the direction ambiguity of ocean waves can be removed by using the imaginary part of cross spectra.