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Remote Sens. 2017, 9(5), 474;

Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions

School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China
Jiangsu Research Center for Ocean Survey and Technology, Nanjing 210044, China
Laboratoire d’Oceanographie Spatiale, Centre de Brest, IFREMER, Plouzané 29280, France
Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, NS B2Y4A2, Canada
Authors to whom correspondence should be addressed.
Academic Editors: Xiaofeng Yang, Xiaofeng Li, Ferdinando Nunziata, Alexis Mouche and Prasad S. Thenkabail
Received: 14 March 2017 / Revised: 18 April 2017 / Accepted: 9 May 2017 / Published: 12 May 2017
(This article belongs to the Special Issue Ocean Remote Sensing with Synthetic Aperture Radar)
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This paper reports Ku-band normalized radar cross section (NRCS) at low incidence angles ranging from 0° to 18° and in the wind speed range from 6 to 70 m/s. The precipitation radar onboard the tropical rainfall measuring mission and Jason-1 and 2 have provided 152 hurricanes observations between 2008 and 2013 that were collocated with stepped-frequency microwave radiometer measurements. It is found that the NRCS decreases with increasing incidence angle. The decrease is more dramatic in the 40–70 m/s range of wind speeds than in the 6–20 m/s range, indicating that the NRCS is very sensitive to low incidence angles under extreme wind conditions and insensitive to the extreme wind speed. Consequently, the sea surface appears relatively “smooth” to Ku-band electromagnetic microwaves. This phenomenon validates the observed drag coefficient reduction under extreme wind conditions, from a remote sensing viewpoint. Using the NRCS dependence on incidence angle under extreme wind conditions, we also present an empirical linear relationship between NRCS and incidence angles, which may assist future-satellites missions operating at small incidence angles to measure sea surface wind and wave field. View Full-Text
Keywords: NRCS; extreme wind conditions; low incidence angles NRCS; extreme wind conditions; low incidence angles

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Li, X.; Zhang, B.; Mouche, A.; He, Y.; Perrie, W. Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions. Remote Sens. 2017, 9, 474.

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