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Remote Sens. 2012, 4(5), 1162-1189; doi:10.3390/rs4051162
Article

Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity

*  and
Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
* Author to whom correspondence should be addressed.
Received: 14 March 2012 / Revised: 16 April 2012 / Accepted: 18 April 2012 / Published: 27 April 2012
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Abstract

Foam fraction can be retrieved from space-based microwave radiometric data at frequencies from 1 to 37 GHz. The retrievals require modeling of ocean surface emissivity fully covered with sea foam. To model foam emissivity well, knowledge of foam properties, both mechanical and dielectric, is necessary because these control the radiative processes in foam. We present a physical description of foam dielectric properties obtained from the foam dielectric constant including foam skin depth; foam impedance; wavelength variations in foam thickness, roughness of foam layer interfaces with air and seawater; and foam scattering parameters such as size parameter, and refraction index. Using these, we analyze the scattering, absorption, reflection and transmission in foam and gain insights into why volume scattering in foam is weak; why the main absorption losses are confined to the wet portion of the foam; how the foam impedance matching provides the transmission of electromagnetic radiation in foam and maximizes the absorption; and what is the potential for surface scattering at the foam layers boundaries. We put all these elements together and offer a conceptual understanding for the high, black-body-like emissivity of foam floating on the sea surface. We also consider possible scattering regimes in foam.
Keywords: passive remote sensing; whitecaps; sea foam; foam fraction; whitecap fraction; foam permittivity; dielectric constant; foam dielectric properties passive remote sensing; whitecaps; sea foam; foam fraction; whitecap fraction; foam permittivity; dielectric constant; foam dielectric properties
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Anguelova, M.D.; Gaiser, P.W. Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity. Remote Sens. 2012, 4, 1162-1189.

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