Ocean wave slope spectra from polarimetric SAR images of the ocean surface

Abstract

Fully-polarimetric SAR measurements have been used successfully to estimate the slopes of natural surfaces in the azimuth direction. The primary thrust of these previous studies has been the use of polarimetric measurements to generate digital elevation maps (DEM) of terrain. In this study, fully-polarimetric SAR measurements of ocean waves from NASA/JPL's AIRSAR are used to estimate the azimuth wave slopes of surface waves. These slope estimates are then used to generate wave slope spectra. The technique follows the approach developed by Schuler and Lee for estimating DEMs. Since the wave slope measurements are small and are extremely sensitive to errors, different algorithms for estimating the slopes were investigated. In addition to this technique for estimating the azimuth wave slopes, a new processing technique is developed for using polarimetric SAR measurements for estimating the range directed wave slopes. The range slope estimates are obtained by using the phase difference between the HH and VV complex images. Initial results indicate that this technique may help to 'fill-in' the spectrum for wave components traveling close to the range direction. The slope spectra derived from the fully-polarized, signatures appear to agree well with the slope spectra derived from the image spectra.