In 2016, the first Chinese synthetic aperture radar (SAR), the Gaofen-3 (GF-3) satellite, was launched. Unlike the single-polarized
wave mode SARs in Europe, GF-3 is the first satellite acquiring the quad-polarized SAR data in wave mode
configuration, which could benefit the ocean wave estimation. Here, the ocean wave spectra estimation from quad-polarized
GF-3 wave mode is presented and its performances are evaluated. For the period from January to October in
2017, the ocean wave spectra were inverted from GF-3 wave mode data. The quad-polarized SAR-ocean spectra inversion
scheme was utilized, in which the azimuthal and range wave slopes are obtained from the vertically and linearly polarized
normalized radar cross sections and then converted to ocean wave slope spectra. The validation was also performed through
comparisons against directional wave buoy observations. The spatio-temporal criteria of 100 km and 0.5 h, yield 87 matchups.
Two representative cases illustrate the consistency between the GF-3 SAR ocean wave spectra and buoy
measurements. Statistical assessment shows the root mean square error (RMSE) of 0.35 m, 19.52 m and 24.89° for the
significant wave height, peak wavelength and wave direction, respectively. Evaluation results indicate that the quad-polarized
algorithm is suitable for spectral ocean wave estimation from GF-3 wave mode, and encouraging for operational
implementation.
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