The measurements of surface waves and wave breaking by Synthetic Aperture Radar near the coast

In this study, Synthetic Aperture Radar images containing surface waves and coastal wave breaking were obtained in conjunction with reference in-situ data near the east coast of Hainan, China during the flight experiment for SAR application at land and sea in 2009. The surface wave spectra and the associated wave parameters retrieved from RADARSAT-2 images are compared with the observation from Wave rider buoy over the study site. The signature of high backscattering signal supposed to be the zone of wave breaking due to shoaling effect is identified in both co- and cross-polarization images. It is shown that the backscattering coefficients of wave breaking zone in cross-polarization images are sufficiently distinct to that from background. Although the significance of wave breaking signal reference to background in co-polarization images is less than that in cross-polarization images due to the interference of wave stripes, the increase of backscattering cross-section of wave breaking zone in quad-polarization images can be determined. The intensity of wave breaking stripe is proportional to the signal to noise ratio of SAR spectrum. The wave spectrum is derived by the inversion of quasi-linear transform which relate the ocean wave spectrum to the SAR image spectrum. The errors of retrieval wave propagation direction of waves for SAR are less than 20° and the errors of the wave height, wave length and wave period is less than 20%, which shows the good agreement of SAR wave parameters with in-situ observation. The results can be used to evaluate the performance of coastal ocean wave observation by space-borne SAR.