The effect of the spatially inhomogeneous wind field on the wave spectra employing an ERS-2 SAR PRI image

Using wave spectra extracted from image mode ERS-2 SAR scenes, the spatial homogeneity of the wave field in deep water is investigated. From the 100×100 km image, several small images of 6.4×6.4 km are selected and the wave spectra are computed. The locally disturbed wind velocity pattern, caused by the sheltering effect of large mountains near the coast, translates into the selected SAR image as regions of higher and lower wind speed. Assuming that the swell field is uniform over the whole image, SAR derived swell spectra retrieved from the sheltered and non-sheltered areas are intercompared. Any difference between them could be related to a possible modification associated with the sheltering effect on the wind speed and/or a possible interaction between wind sea and swell, since the wind sea part of the spectrum would be slightly different due to the different wind speeds. The results show that there is no significant modification, and apparently there is no clear difference in the swell spectra despite the different wind sea components and wind speeds.

► We have examined the spatial homogeneity of ERS-2 SAR wave spectra. ► The sheltering effect of the mountains formed regions with different wind speeds. ► The aim is to investigate how/if the SAR retrieved swell wave spectrum is affected. ► There is no clear difference among the spectra computed over the different regions. ► There is no significant effect of the variable wind speed on the swell spectra.