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

Type Article
Date 2017-05
Language English
Author(s) Li Xiuzhong1, 2, Zhang Biao1, 2, Mouche AlexisORCID1, 3, He Yijun1, 2, Perrie William1, 4
Affiliation(s) 1 : Nanjing Univ Informat Sci & Technol, Sch Marine Sci, Nanjing 210044, Jiangsu, Peoples R China.
2 : Jiangsu Res Ctr Ocean Survey & Technol, Nanjing 210044, Jiangsu, Peoples R China.
3 : IFREMER, Ctr Brest, Lab Oceanog Spatiale, F-29280 Plouzane, France.
4 : Fisheries & Oceans Canada, Bedford Inst Oceanog, Dartmouth, NS B2Y 4A2, Canada.
Source Remote Sensing (2072-4292) (Mdpi Ag), 2017-05 , Vol. 9 , N. 5 , P. 474 (1-14)
DOI 10.3390/rs9050474
WOS© Times Cited 9
Keyword(s) NRCS, extreme wind conditions, low incidence angles

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.

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