Influence of the wind field on the radiance of a marine shallow: evidence from the Caspian Sea

The influence of the near-water wind field on the radiance of a marine shallowwas studied on the basis of daily SeaWiFS ocean colour scanner data andQuickScat scatterometer wind data collected from 1999 to 2004 in the southernCaspian Sea, where the deep basin borders a vast shallow west of the shore ofmeridional extent. It was found that radiance distributions, clustered bywind rhumbs, exhibited different long-term mean patterns for winds of opposingdirections: within the shallow's boundaries, the radiances were about twice ashigh for winds having an offshore component with reference to the onshore windconditions. The zonal profile of radiance across the shallow resembleda closed loop whose upper and lower branches corresponded to the offshore and onshore winds respectively. Theloop was the most pronounced at sites with 10-15 m of water for any wavelengthof light, including the red region. On the basis of specific features of the studyarea, we attributed this pattern to sunlight backscattered from bottom sedimentsresuspended by bottom compensation currents induced by the offshorewinds.