Abstract
This study analyzed the noise equivalent sigma zero (NESZ) and ocean wind sensitivity for Chinese C-band Gaofen-3 (GF-3) quad-polarization synthetic aperture radar (SAR) measurements to facilitate further operational wind extraction from GF-3 data. Data from the GF-3 quad-polarization SAR and collocated winds from both NOAA/NCEP Global Forecast System (GFS) atmospheric model and National Data Buoy Center (NDBC) buoys were used in the analysis. For NESZ, the co-polarization was slightly higher compared to the cross-polarization. Regarding co-polarization and cross-polarization, NESZ was close to RadarSAT-2 and Sentinel-1 A. Wind sensitivity was analyzed by evaluating the dependence on winds in terms of normalized radar cross-sections (NRCS) and polarization combinations. The closest geophysical model function (GMF) and the polarization ratio (PR) model to GF-3 data were determined by comparing data and the model results. The dependence of co-polarized NRCS on wind speed and azimuth angle was consistent with the proposed GMF models. The combination of CMOD5 and CMOD5.N was considered to be the closest GMF in co-polarization. The cross-polarized NRCS exhibited a strong linear relationship with moderate wind speeds higher than 4 m·s−1, but a weak correlation with the azimuth angle. The proposed model was considered as the closest GMF in cross-polarization. For polarization combinations, PR and polarization difference (PD) were considered. PR increased only with the incidence angle, whereas PD increased with wind speed and varied with azimuth angle. There were three very close PR models and each can be considered as the closest. Preliminary results indicate that GF-3 quad-polarization data are valid and have the ability to extract winds in each polarization.
Highlights
Spaceborne C-band synthetic aperture radar (SAR) can measure high-resolution sea surface normalized radar cross-sections (NRCS)
The cross-polarization noise equivalent sigma zero (NESZ) for both RS-2 and S1-A SAR were approximately −35 dB [12,13]. This provides a preliminary indication that GF-3 data have an NESZ level comparable with S-1A and RS-2 in each polarization within this incidence angle range
This study focuses on the preliminary analysis of NESZ and wind sensitivity for Chinese GF-3 SAR measurements
Summary
Spaceborne C-band synthetic aperture radar (SAR) can measure high-resolution sea surface normalized radar cross-sections (NRCS). The SAR-derived NRCS originate from Bragg scattering, which arose from the resonant interaction between radar transmitting magnetic waves and centimeter-scale short waves [1]. Through this interaction, the NRCS can be related to radar geometry and sea surface characteristics (wind and waves). With the development of polarimetric SAR technology, an increasing number of polarization configurations have been attempted on SAR. This polarization diversity will inevitably deliver new features to the SAR data or the GMF
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