Remote Sensing of Organic Films on the Water Surface Using Dual Co-Polarized Ship-Based X-/C-/S-Band Radar and TerraSAR-X

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.

[1]  Reinhard Miller,et al.  Static and dynamic surface tension of marine water: onshore or platform-based measurements by the oscillating bubble tensiometer , 2006 .

[2]  Torbjørn Eltoft,et al.  Comparing Near-Coincident C- and X-Band SAR Acquisitions of Marine Oil Spills , 2015, IEEE Transactions on Geoscience and Remote Sensing.

[3]  Heinrich Hühnerfuss,et al.  Imaging of biogenic and anthropogenic ocean surface films by the multifrequency/multipolarization SIR‐C/X‐SAR , 1998 .

[4]  S. A. Ermakov,et al.  Damping of gravity-capillary waves in the presence of oil slicks according to data from laboratory and numerical experiments , 2012, Izvestiya, Atmospheric and Oceanic Physics.

[5]  S. G. Salashin,et al.  Surface film effect on short wind waves , 1986 .

[6]  Stanley J. Jacobs,et al.  Wave damping by a thin layer of viscous fluid , 1997 .

[7]  A. Solberg,et al.  Oil spill detection by satellite remote sensing , 2005 .

[8]  G. Valenzuela.  Theories for the interaction of electromagnetic and oceanic waves — A review , 1978 .

[9]  Bertrand Chapron,et al.  Wave Breaking in Slicks: Impacts on C-Band Quad-Polarized SAR Measurements , 2016, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[10]  Daniel S. Kwoh,et al.  The Nature of Microwave Backscattering from Water Waves , 1985 .

[11]  W. Alpers,et al.  The damping of ocean waves by surface films: A new look at an old problem , 1989 .

[12]  Benjamin Holt,et al.  Polarimetric Analysis of Backscatter From the Deepwater Horizon Oil Spill Using L-Band Synthetic Aperture Radar , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[13]  I. Sergievskaya,et al.  Remote sensing of oil films on the water surface using radar , 2012, Remote Sensing.

[14]  Irina Sergievskaya,et al.  Damping of gravity–capillary waves on water surface covered with a visco-elastic film of finite thickness , 2017, Izvestiya, Atmospheric and Oceanic Physics.

[15]  S. G. Salashin,et al.  Film slicks on the sea surface and some mechanisms of their formation , 1992 .

[16]  R. P. Cleaver,et al.  Crest instabilities of gravity waves. Part 1. The almost-highest wave , 1994, Journal of Fluid Mechanics.

[17]  S. A. Ermakov,et al.  Laboratory study of the damping of parametric ripples due to surfactant films , 2006 .

[18]  B. Chapron,et al.  A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model , 2003 .

[19]  Heinrich Hühnerfuss,et al.  Wave damping by monomolecular surface films and their chemical structure. Part II: Variation of the hydrophilic part of the film molecules including natural substances , 1984 .

[20]  Andrew T. Jessup,et al.  Measurements of sea spikes in microwave backscatter at moderate incidence , 1990 .

[21]  M. Longuet-Higgins,et al.  Parasitic capillary waves: a direct calculation , 1995, Journal of Fluid Mechanics.

[22]  M. Donelan,et al.  Radar scattering and equilibrium ranges in wind‐generated waves with application to scatterometry , 1987 .

[23]  Olga V. Shomina,et al.  On the Doppler Frequency Shifts of Radar Signals Backscattered from the Sea Surface , 2014 .

[24]  F. Bass,et al.  Wave scattering from statistically rough surfaces , 1979 .

[25]  E. H. Lucassen-Reynders,et al.  Properties of capillary waves , 1970 .

[26]  O. Phillips.  Spectral and statistical properties of the equilibrium range in wind-generated gravity waves , 1985, Journal of Fluid Mechanics.

[27]  I. A. Kapustin,et al.  On peculiarities of scattering of microwave radar signals by breaking gravity-capillary waves , 2012 .

[28]  Heinrich Hühnerfuss,et al.  Wind‐wave tank measurements of bound and freely propagating short gravity‐capillary waves , 1998 .

[29]  O. M. Phillips,et al.  Radar Returns from the Sea Surface—Bragg Scattering and Breaking Waves , 1988 .

[30]  S. V. Kijashko,et al.  Role of surface films in ERS SAR signatures of internal waves on the shelf: 1. Short-period internal waves , 1998 .

[31]  Bertrand Chapron,et al.  On Dual Co-Polarized SAR Measurements of the Ocean Surface , 2013, IEEE Geoscience and Remote Sensing Letters.

[32]  B. Lake,et al.  A deterministic, coherent, and dual-polarized laboratory study of microwave backscattering from water waves, Part I: Short gravity waves without wind , 1984, IEEE Journal of Oceanic Engineering.