Retrieval of sea surface winds under hurricane conditions from GNSS-R observations
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Retrieval of sea surface winds under hurricane conditions from GNSS-R observations JING Cheng1, YANG Xiaofeng1*, MA Wentao1, YU Yang1, DONG Di1, LI Ziwei1, XU Cong2 1 State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of
Sciences, Beijing 100101, China 2 National Engineering Center for Geoinformatics, Institute of Remote Sensing and Digital Earth, Chinese Academy of
Sciences, Beijing 100101, China Received 14 October 2015; accepted 11 January 2016 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
Reflected signals from global navigation satellite systems (GNSSs) have been widely acknowledged as an important remote sensing tool for retrieving sea surface wind speeds. The power of GNSS reflectometry (GNSS-R) signals can be mapped in delay chips and Doppler frequency space to generate delay Doppler power maps (DDMs), whose characteristics are related to sea surface roughness and can be used to retrieve wind speeds. However, the bistatic radar cross section (BRCS), which is strongly related to the sea surface roughness, is extensively used in radar. Therefore, a bistatic radar cross section (BRCS) map with a modified BRCS equation in a GNSS-R application is introduced. On the BRCS map, three observables are proposed to represent the sea surface roughness to establish a relationship with the sea surface wind speed. Airborne Hurricane Dennis (2005) GNSS-R data are then used. More than 16 000 BRCS maps are generated to establish GMFs of the three observables. Finally, the proposed model and classic one-dimensional delay waveform (DW) matching methods are compared, and the proposed model demonstrates a better performance for the high wind speed retrievals. Key words: global navigation satellite system-reflectometry, Hurricane Dennis, delay doppler maps, bistatic radar cross section map, sea surface wind speed Citation: Jing Cheng, Yang Xiaofeng, Ma Wentao, Yu Yang, Dong Di, Li Ziwei, Xu Cong. 2016. Retrieval of sea surface winds under hurricane conditions from GNSS-R observations. Acta Oceanologica Sinica, 35(9): 91–97, doi: 10.1007/s13131-016-0933-7
1 Introduction Global navigation satellite systems not only supply users with position information, but they also continuously emit L-band microwaves onto the earth’s surface. Since Martin-Neira (1993) proposed a passive reflectometry and interferometry system (PARIS) concept as a means to measure sea surface heights using reflected signals from global navigation satellite systems (GNSS) satellites, the GNSS reflectometry (GNSS-R) has been widely used in many fields including sea surface wind field retrieval, studies of soil moisture, sea ice and oil slicks and even target detection. In 1996, Katzberg and Garrison (1996) suggested the concept of using low earth orbit (LEO) satellites to receive sea surface reflected GPS signals. Subsequently, they completed several flight experiments with different sea states and verified the relationship between the time-delay coherent power
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