Radar and optical measurements of damping of small-scale wind waves in artificial slicks

Damping of short centimetre-millimetre (cm-mm)-scale wind waves was studied during experiments conducted from a platform in the Black Sea. During the experiments artificial organic slicks were observed using Ka-band and X-band radars and using optical spectrum analysers. Film sampling from the artificial slicks with small nylon nets was also performed and the film elasticity was later estimated from laboratory measurements of wave damping. One of the experiments was conducted during an ERS-2 satellite overpass and the slick was imaged by the C-band ERS-2 SAR. It is shown that damping of mm-scale waves exceeds the damping of cm-dm-waves and exhibits a maximum at surface wavelengths about 5-7 mm. The maximum is assumed to be a manifestation of a new nonlinear mechanism of damping of “parasitic” capillary ripples generated on the slopes of decimetre (dm)-scale wind waves