The impact of rain to observed signal from Chinese Gaofen-3 synthetic aperture radar in typhoons
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The impact of rain to observed signal from Chinese Gaofen-3 synthetic aperture radar in typhoons Jian Shi1, Jiachen Hu2, Weizeng Shao2*, Xiaoqing Wang3, Xinzhe Yuan4, Liangbo Zhao5, Xiaofeng Li2 1 College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China 2 Marine Science and Technology College, Zhejiang Ocean University, Zhoushan 316022, China 3 School of Electronics and Communication Engineering, Sun Yat-sen University, Guangzhou 510275, China 4 Key Laboratory of Space Ocean Remote Sensing and Application, National Satellite Ocean Application Service,
Beijing 100081, China 5 Institute of Spacecraft System Engineering, China Academy of Space Technology, Beijing 100094, China
Received 28 May 2019; accepted 2 September 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
Gaofen-3 (GF-3), a Chinese civil synthetic aperture radar (SAR) at C-band, has operated since August 2016. Remarkably, several typhoons have been captured by GF-3 around the China Seas over its last two-year mission. In this study, six images acquired in Global Observation (GLO) and Wide ScanSAR (WSC) modes at verticalvertical (VV) polarization channel are discussed. This work focuses on investigating the observation of rainfall using GF-3 SAR. These images were collocated with winds from the European Centre for Medium-Range Weather Forecasts (ECMWF), significant wave height simulated from the WAVEWATCH-III (WW3) model, sea surface currents from climate forecast system version 2 (CFSv2) of the National Centers for Environmental Prediction (NCEP) and rain rate data from the Tropical Rainfall Measuring Mission (TRMM) satellite. Sea surface roughness, was compared with the normalized radar cross section (NRCS) from SAR observations, and indicated a 0.8 correlation (COR). We analyzed the dependences of the difference between model-simulated NRCS and SARmeasured NRCS on the TRMM rain rate and WW3-simulated significant wave height. It was found that the effects of rain on SAR damps the radar signal at incidence angles ranging from 15° to 30°, while it enhances the radar signal at incidence angles ranging from 30° to 45° and incidence angles smaller than 10°. This behavior is consistent with previous studies and an algorithm for rain rate retrieval is anticipated for GF-3 SAR. Key words: Gaofen-3, synthetic aperture radar, typhoon Citation: Shi Jian, Hu Jiachen, Shao Weizeng, Wang Xiaoqing, Yuan Xinzhe, Zhao Liangbo, Li Xiaofeng. 2019. The impact of rain to observed signal from Chinese Gaofen-3 synthetic aperture radar in typhoons. Acta Oceanologica Sinica, 38(11): 121–133, doi: 10.1007/s13131-019-1502-7
1 Introduction Typhoons are a natural disaster in coastal areas, and in particular, rainfall is always accompanied with strong winds. The track and category of a typhoon can be monitored by means of passive optical satellites, e.g., moderate-resolution imaging spectroradiometer (MODIS) of Earth Observation System (EOS). However, sea surface informa
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