Evaluation of Chinese Quad-polarization Gaofen-3 SAR Wave Mode Data for Significant Wave Height Retrieval

Abstract

Our work describes the accuracy of the Chinese quad-polarization Gaofen-3 (GF-3) synthetic aperture radar (SAR) wave mode data for wave retrieval and provides guidance for operational applications of GF-3 SAR. In this study, we have evaluated the accuracy of SAR-derived significant wave height (SWH) from 10514 GF-3 SAR images with visible wave streak acquired in wave mode by using the existing wave retrieval algorithms, e.g., the theoretical-based algorithm parameterized first-guess spectrum method (PFSM), the empirical algorithm CSAR_WAVE2 for VV-polarization, and the algorithm for quad-polarization (Q-P). The retrieved SWHs are compared with the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis field at 0.125° grids. The root mean square error (RMSE) of SWH is 0.57m by using CSAR_WAVE2 is achieved, which is less than the analysis results achieved by using algorithm PFSM and Q-P. The statistical analysis also indicates that wind speed has little impact on bias with increasing wind speed.However, the retrieval tends to overestimate when SWH is smaller than 2.5m and

Ship Detection and Feature Visualization Analysis Based on Lightweight CNN in VH and VV Polarization Images

“…Figure 12 shows the detection result and Table 10 presents the evaluation index of VV polarization in the No.4 sub-image of the Huanghai Sea area. Different from the VH polarization in Figure 10, the VV polarization image shows an inhomogeneous pattern in the SAR scene due to other marine phenomena that may exist in the images, e.g., moderate-to-high wind, upwelling, and eddies [45,46]. In those methods, the RF shows the better performance with an F1 score of 0.97 and an accuracy of 99.35% than other methods.…”

Modulation Effects of Mesoscale Eddies on Sea Surface Wave Fields in the South China Sea Derived From a Wave Spectrometer Onboard the China‐France Ocean Satellite

“…Spaceborne SAR is a powerful, high‐resolution (up to O(1) m) imaging sensor for 2‐D sea surface wave fields. From SAR images, investigators can directly obtain the wavelength and propagation direction of the surface waves, empirically estimate the SWH and retrieve the directional spectra, which are essential for wave dynamic analysis and sea state forecasting (Aouf & Lefevre, 2013; Ardhuin et al., 2009; Collard et al., 2005; Engen & Johnsen, 1995; Ji et al., 2018; Li et al., 2020; Shao et al., 2016; Zhu et al., 2018). However, the azimuth‐cutoff effect on SAR imaging ability restricts the retrieved information to long waves with wavelengths generally longer than 250 m and/or to waves traveling in a direction perpendicular to the satellite ground track (Alpers & Bruening, 1986; Hauser et al., 2017).…”

Wind speed retrieval from the Gaofen-3 synthetic aperture radar for VV- and HH-polarization using a re-tuned algorithm

“…It is well known that Synthetic Aperture Radar (SAR) is one of the most efficient instruments for observing the sea surface at high spatial resolution over large areas. For example, the C-band Chinese Gaofen-3 (GF-3) SAR (5.43 GHz) has 8-m/25-m nominal resolution spacing and 30-km/40-km nominal swath coverage for quad-polarization stripmap-I/II (QPS-I/II) mode (Shao et al, 2019a) and a 10-m nominal resolution spacing and 50-km nominal swath coverage for GF-3 SAR in wave (WV) mode (Shao et al, 2019b;Zhu et al, 2018). In the literature, SARmeasured normalized radar cross-sections (NRCS) in the Vertical-Vertical (VV) and Horizontal-Horizontal (HH)-polarized channels, are directly related to the wind vector 10 m above the sea surface (Koch & Feser, 2006;Masuko et al, 1986).…”