Abstract
Microwave radar is a well-established tool for all-weather monitoring of film slicks which appear in radar imagery of the surface of water bodies as areas of reduced backscatter due to suppression of short wind waves. Information about slicks obtained with single-band/one-polarized radar seems to be insufficient for film characterization; hence, new capabilities of multi-polarization radars for monitoring of film slicks have been actively discussed in the literature. In this paper the results of new experiments on remote sensing of film slicks using dual co-polarized radars—a satellite TerraSAR-X and a ship-based X-/C-/S-band radar—are presented. Radar backscattering is assumed to contain Bragg and non-Bragg components (BC and NBC, respectively). BC is due to backscattering from resonant cm-scale wind waves, while NBC is supposed to be associated with wave breaking. Each of the components can be eliminated from the total radar backscatter measured at two co-polarizations, and contrasts of Bragg and non-Bragg components in slicks can be analyzed separately. New data on a damping ratio (contrast) characterizing reduction of radar returns in slicks are obtained for the two components of radar backscatter in various radar bands. The contrast values for Bragg and non-Bragg components are comparable to each other and demonstrate similar dependence on radar wave number; BC and NBC contrasts grow monotonically for the cases of upwind and downwind observations and weakly decrease with wave number for the cross-wind direction. Reduction of BC in slicks can be explained by enhanced viscous damping of cm-scale Bragg waves due to an elastic film. Physical mechanisms of NBC reduction in slicks are discussed. It is hypothesized that strong breaking (e.g., white-capping) weakly contributes to the NBC contrast because of “cleaning” of the water surface due to turbulent surfactant mixing associated with wave crest overturning. An effective mechanism of NBC reduction due to film can be associated with modification of micro-breaking wave features, such as parasitic ripples, bulge, and toe, in slicks.
Highlights
Pollution of the sea surface is an imminent threat for the ecological state of open ocean, coastal zones, and inland waters
This paper presents new results of studies of film slicks using dual co-polarized radar: the satellite TerraSAR-X and an X-/C-/S-band scatterometer mounted onboard a research vessel
Organic films of oleic acid deployed on the water surface were observed using dual-polarized TerraSAR-X and an X-/C-/S-band dual-polarized microwave radars
Summary
Pollution of the sea surface is an imminent threat for the ecological state of open ocean, coastal zones, and inland waters. Remote sensing of marine films, both biogenic pollutions and oil spills, is aimed to identify the films and to quantify their characteristics, and is a very important and urgent problem actively discussed in the literature (see, [1,2,3,4,5,6,7], and references therein). This problem, is still far from a comprehensive solution. Film slicks appear in radar imagery of the sea surface as areas of reduced radar backscatter, and the latter is essentially a result of enhanced suppression of short wind waves
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
