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Remote Sens. 2019, 11(7), 839;

Sea Surface Ka-Band Doppler Measurements: Analysis and Model Development

Remote Sensing Department, Marine Hydrophysical Institute of RAS, 2 Kapitanskaya St., 299011 Sevastopol, Russia
Satellite Oceanography Laboratory, Russian State Hydrometeorological University, 98 Malookhtinskiy Pr., 195196 St-Petersburg, Russia
Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20740, USA
Spatial and Physical Oceanography Laboratory, Institut Français de Recherche pour l’Exploitation de la Mer, 29280 Plouzané, France
Author to whom correspondence should be addressed.
Received: 26 February 2019 / Revised: 1 April 2019 / Accepted: 4 April 2019 / Published: 8 April 2019
(This article belongs to the Section Ocean Remote Sensing)
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Multi-year field measurements of sea surface Ka-band dual-co-polarized (vertical transmit–receive polarization (VV) and horizontal transmit–receive polarization (HH)) radar Doppler characteristics from an oceanographic platform in the Black Sea are presented. The Doppler centroid (DC) estimated using the first moment of 5 min averaged spectrum, corrected for measured sea surface current, ranges between 0 and ≈1 m/s for incidence angles increasing from 0 to 70 . Besides the known wind-to-radar azimuth dependence, the DC can also depend on wind-to-dominant wave direction. For co-aligned wind and waves, a negative crosswind DC residual is found, ≈−0.1 m/s, at ≈20 incidence angle, becoming negligible at ≈ 60 , and raising to, ≈+0.5 m/s, at 70 . For our observations, with a rather constant dominant wave length, the DC is almost wind independent. Yet, results confirm that, besides surface currents, the DC encodes an expected wave-induced contribution. To help the interpretation, a two-scale model (KaDOP) is proposed to fit the observed DC, based on the radar modulation transfer function (MTF) previously developed for the same data set. Assuming universal spectral shape of energy containing sea surface waves, the wave-induced DC contribution is then expressed as a function of MTF, significant wave height, and wave peak frequency. The resulting KaDOP agrees well with independent DC data, except for swell-dominated cases. The swell impact is estimated using the KaDOP with a modified empirical MTF. View Full-Text
Keywords: radar; scatterometer; ocean; backscatter; Doppler shift; Doppler centroid; sea surface current; wind drift; modulation; transfer function; empirical model radar; scatterometer; ocean; backscatter; Doppler shift; Doppler centroid; sea surface current; wind drift; modulation; transfer function; empirical model

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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 (CC BY 4.0).

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Yurovsky, Y.Y.; Kudryavtsev, V.N.; Grodsky, S.A.; Chapron, B. Sea Surface Ka-Band Doppler Measurements: Analysis and Model Development. Remote Sens. 2019, 11, 839.

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