Observations of radar/optical slick signatures of marine processes in the coastal zone

Abstract

Analysis of possibilities of identification and characterization of marine processes using their signatures in radar and optical imagery of the sea surface is a very important problem of the ocean remote sensing which has not been solved yet completely by now. Marine slicks which are the areas of suppressed wind waves can be recorded by different sensors and can be indicators of internal waves, non uniform currents, atmospheric convective cells, etc. Field studies including those simultaneous and co-located with remote observations is the most perspective way to the problem solution. An expedition of the Institute of Applied Physics RAS was organized to study the nature of slick bands and its dynamics in the field of various subsurface processes. Field experiments were carried out in the coastal zone of the Black sea from the Oceanographic Platform of Marine Hydrophysical Institute RAS and from the shore. The structure of the currents in the studied area is characterized by significant heterogeneity, so we were able to register different slick structures in the flow field and wind and the slick dynamics. In some experiments, marine slicks were recorded simultaneously in satellite Sentinel images. Observations of surface manifestations of internal waves were carried out using a digital radar station MRS-1000 and multi-frequency radar complex of IAP RAS. At the same time the measurements of currents in the water column were carried out using the ADCP WH Monitor 1200 kHz, wind speed and direction at a height of 30 meters using WindSonic acoustic anemometer. During the passage of internal waves a system of slick bands with a reduced intensity of small-scale waves were observed. Slick bands were observed mainly over the rear slopes of the internal waves; the data from the accompanying measurements showed that the phase velocity was close to the surface current velocity. Theoretical analysis has shown that in this case the convergent zones, where surfactants are accumulated were formed at the rear slopes of the internal waves. This mechanism of slick formation was predicted earlier theoretically and then was modeled in laboratory experiment.