On discrimination between film slicks and 'look-alikes' on the sea surface in multifrequency radar images

摘要

Slicks on the sea surface are characterized by attenuation of short wind waves and appear in radar imagery at moderate incidence angles as areas of reduced intensity. In the proximity of oil platforms, ship routes, fish farms, etc. marine slicks are often identified as oil spills or biogenic films. However, probability of false alarm when detecting film slicks is very high because of the occurrence of structures in radar images looking similar but not related to surface films ("look-alikes"). One of the most frequent "look-alikes" is wind depression areas (WDAs) where the wind excitation of short surface waves is reduced compared to the ambient background. Results of field observations of films slicks and WDA are described and differences in character of wind wave attenuation in different parts of the wind wave spectrum are revealed. Model calculations of wave damping degree (contrast) in film slick and in WDA are carried out and are shown to be in general agreement with experiment. Capabilities of dual-polarization and multi-band microwave radar for discrimination between film slicks and "look-alikes" are analyzed based on experiment and model results.