Ka-Band Radar Cross-Section of Breaking Wind Waves

Type Article
Date 2021-05
Language English
Author(s) Yurovsky Yury Yu.ORCID1, Kudryavtsev Vladimir N.ORCID1, 2, Grodsky Semyon A.ORCID3, Chapron BertrandORCID2, 4
Affiliation(s) 1 : Applied Marine Physics Laboratory, Marine Hydrophysical Institute Russian Academy Sci., 2 Kapitanskaya, 299011 Sevastopol, Russia
2 : Satellite Oceanography Laboratory, Russian State Hydrometeorological University, 98 Malookhtinskiy, 195196 Saint Petersburg, Russia
3 : Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742, USA
4 : Laboratoire d’Océanographie Physique Spatiale, Institut Français de Recherche pour l’Exploitation de la Mer, 29280 Plouzané, France
Source Remote Sensing (2072-4292) (MDPI AG), 2021-05 , Vol. 13 , N. 10 , P. 1929 (17p.)
DOI 10.3390/rs13101929
Note This article belongs to the Section Ocean Remote Sensing
Keyword(s) radar, ocean, backscatter, Ka-band, field measurements, breaking wave, breaker, normalized radar cross-section, Lambda-distribution

The effective normalized radar cross section (NRCS) of breaking waves, σwb, is empirically derived based on joint synchronized Ka-band radar and video records of the sea surface from a research tower. The σwb is a key parameter that, along with the breaker footprint fraction, Q, defines the contribution of non-polarized backscattering, NP =σwbQ, to the total sea surface NRCS. Combined with the right representation of the regular Bragg and specular backscattering components, the NP component is fundamental to model and interpret sea surface radar measurements. As the first step, the difference between NRCS values for breaking and non-breaking conditions is scaled with the optically-observed Q and compared with the geometric optics model of breaker backscattering. Optically-derived Q might not be optimal to represent the effect of breaking waves on the radar measurements. Alternatively, we rely on the breaking crest length that is firmly detected by the video technique and the empirically estimated breaker decay (inverse wavelength) scale in the direction of breaking wave propagation. A simplified model of breaker NRCS is then proposed using the geometric optics approach. This semi-analytical model parameterizes the along-wave breaker decay from reported breaker roughness spectra, obtained in laboratory experiments with mechanically-generated breakers. These proposed empirical breaker NRCS estimates agree satisfactorily with observations.

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