Evaluation of radar contrasts in film slicks at high winds

Abstract

The investigation of surface film pollution is extremely important for ocean ecology and developing the methods of ocean remote sensing. The goal of this work is an experimental study of parameters of surfactant films in real conditions on the sea surface and their effect on measured radar return contrast in the film slicks. The properties of films of oleic acid in real conditions were studied under moderate winds in the Gorky Reservoir. Previously, the dependence of the elasticity and the surface tension coefficient of the oleic acid film (the parameters that determine the wave damping) on the surface of the distilled liquid were studied in detail in our laboratory. To study the properties of the film on the water surface under real conditions, a surfactant was sprayed onto the water surface, after which surface samples were taken using a net method. The film concentration and elasticity of the film were retrieved in the IAP laboratory. It is shown that the mean surface concentration of the film is several times higher than the concentration of the monomolecular layer of oleic acid. In different areas of the film slick, the concentration can vary by 2-3 times. The elasticity of the film formed by oleic acid on the water surface in real conditions is approximately two times less than the elasticity of the oleic acid film previously measured in laboratory conditions. The retrieved elasticity was used to explain the suppression of the X-band radar signal operating at VV polarization at an incidence angle of 60 degrees. To calculate the damping, a model was used that takes into account nonlinear sources of wind wave generation. Using the new elasticity value improves the agreement between the measured and calculated data.