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 shallow was studied on the basis of daily SeaWiFS ocean colour scanner data and QuickScat scatterometer wind data collected from 1999 to 2004 in the southern Caspian Sea, where the deep basin borders a vast shallow west of the shore of meridional extent. It was found that radiance distributions, clustered by wind rhumbs, exhibited different long-term mean patterns for winds of opposing directions: within the shallow’s boundaries, the radiances were about twice as high for winds having an offshore component with reference to the onshore wind conditions. The zonal profile of radiance across the shallow resembled a closed loop whose upper and lower branches corresponded to the offshore and onshore winds respectively. The loop was the most pronounced at sites with 10–15 m of water for any wavelength of light, including the red region. On the basis of specific features of the study area, we attributed this pattern to sunlight backscattered from bottom sediments resuspended by bottom compensation currents induced by the offshore winds.