Abstract
The Chinese Gaofen-3 (GF-3) synthetic aperture radar (SAR) launched by the China Academy of Space Technology (CAST) has operated at C-band since September 2016. To date, we have collected 16/42 images in vertical-vertical (VV)/horizontal-horizontal (HH) polarization, covering the National Data Buoy Center (NDBC) buoy measurements of the National Oceanic and Atmospheric Administration (NOAA) around U.S. western coastal waters. Wind speeds from NDBC in situ buoys are up to 15 m/s and buoy-measured significant wave height (SWH) has ranged from 0.5 m to 3 m. In this study, winds were retrieved using the geophysical model function (GMF) together with the polarization ratio (PR) model and waves were retrieved using a new empirical algorithm based on SAR cutoff wavelength in satellite flight direction, herein called CSAR_WAVE. Validation against buoy measurements shows a 1.4/1.9 m/s root mean square error (RMSE) of wind speed and a 24/23% scatter index (SI) of SWH for VV/HH polarization. In addition, wind and wave retrieval results from 166 GF-3 images were compared with the European Centre for Medium-Range Weather Forecasts (ECMWF) re-analysis winds, as well as the SWH from the WaveWatch-III model, respectively. Comparisons show a 2.0 m/s RMSE for wind speed with a 36% SI of SWH for VV-polarization and a 2.2 m/s RMSE for wind speed with a 37% SI of SWH for HH-polarization. Our work gives a preliminary assessment of the wind and wave retrieval results from GF-3 SAR images for the first time and will provide guidance for marine applications of GF-3 SAR.
Highlights
The Chinese Gaofen-3 (GF-3) satellite was launched on 10 August 2016 by the China Academy of Space Technology (CAST), and carries a C-band (~5.3 GHz) synthetic aperture radar (SAR) sensor with different polarizations
Through a cooperation project between the National Satellite Ocean Application Service (NSOAS) and our institutes, a number of images have been recorded of whole open seas, covering the National Data Buoy Center (NDBC) in situ buoys of the National Oceanic and Atmospheric Administration (NOAA) around U.S western coastal areas
Wind and wave retrieval results from 58 GF-3 images in co-polarization were validated against NDBC in situ buoy measurements around the U.S western coastal area, including wind speed and significant wave height (SWH)
Summary
The Chinese Gaofen-3 (GF-3) satellite was launched on 10 August 2016 by the China Academy of Space Technology (CAST), and carries a C-band (~5.3 GHz) synthetic aperture radar (SAR) sensor with different polarizations. It has 12 imaging modes with a spatial resolution of image ranging from 1 m to 500 m and a swath coverage ranging from 10 to 650 km. Wind and wave monitoring are the two main marine applications of SAR in all-weather conditions, especially in tropical cyclones [1,2]. Bragg waves are produced by sea surface winds.
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