Comparison of WindSat and buoy-measured ocean products from 2004 to 2013
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Comparison of WindSat and buoy-measured ocean products from 2004 to 2013 ZHANG Lei1, SHI Hanqing1, DU Huadong1*, ZHU Enze, ZHANG Zhihua1, FANG Xun1 1 Institute of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing 211101, China
Received 20 November 2014; accepted 5 June 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
To evaluate the ocean surface wind vector and the sea surface temperature obtained from WindSat, we compare these quantities over the time period from January 2004 to December 2013 with moored buoy measurements. The mean bias between the WindSat wind speed and the buoy wind speed is low for the low frequency wind speed product (WSPD_LF), ranging from –0.07 to 0.08 m/s in different selected areas. The overall RMS error is 0.98 m/s for WSPD_LF, ranging from 0.82 to 1.16 m/s in different selected regions. The wind speed retrieval result in the tropical Ocean is better than that of the coastal and offshore waters of the United States. In addition, the wind speed retrieval accuracy of WSPD_LF is better than that of the medium frequency wind speed product. The crosstalk analysis indicates that the WindSat wind speed retrieval contains some cross influences from the other geophysical parameters, such as sea surface temperature, water vapor and cloud liquid water. The mean bias between the WindSat wind direction and the buoy wind direction ranges from –0.46° to 1.19° in different selected regions. The overall RMS error is 19.59° when the wind speed is greater than 6 m/s. Measurements of the tropical ocean region have a better accuracy than those of the US west and east coasts. Very good agreement is obtained between sea surface temperatures of WindSat and buoy measurements in the tropical Pacific Ocean; the overall RMS error is only 0.36°C, and the retrieval accuracy of the low latitudes is better than that of the middle and high latitudes. Key words: WindSat, polarimetric microwave radiometer, wind vector, sea surface temperature, validation Citation: Zhang Lei, Shi Hanqing, Du Huadong, Zhu Enze, Zhang Zhihua, Fang Xun. 2016. Comparison of WindSat and buoy-measured ocean products from 2004 to 2013. Acta Oceanologica Sinica, 35(1): 67–78, doi: 10.1007/s13131-016-0798-9
1 Introduction Ocean surface wind is an essential parameter for the studies of marine waves, water mass, ocean circulation, marine atmospheric boundary layer and air-sea interaction. Modulating the fluxes of heat, moisture, and gas between the atmosphere and the ocean, the wind vector plays a crucial role in studying the regional and global weather and climate. WindSat, as the first spaceborne polarimetric microwave radiometer, was launched in January 2003 by the U.S. Naval Research Laboratory aboard the Department of Defense Coriolis satellite. The chief objective of WindSat is to test and demonstrate the capabilities of a fully polarimetric radiometer to measure sea surface wind speed and wind direction from space. In addition, WindSat can also measure other atmosphe
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