# First Assessment of GF3-02 SAR Ocean Wind Retrieval
## 5 Conclusions  
In this paper, the wind speed of the co-polarization obtained by the GF3-02 SAR from January to March 2022 is retrieved, and a more detailed comparative analysis is made with the wind speed measured by buoys of NDBC and ERA5 wind. For the VV polarization, the experimental results show that the optimal wind speed retrieval function is CMOD5.N. Compared with NDBC, ERA5, and HY-2B SCA wind speeds, the RMSE is 1.40 m/s, 1.18 m/s, and 1.24 m/s, respectively. For the HH polarization, the experimental results show that the optimal wind speed retrieval function is the CMODH_HH model. Compared with NDBC wind speed, ERA5 wind speed, and HY-2B SCA wind speed, the RMSE is 1.45 m/s, 1.19 m/s, and 1.52 m/s, respectively. Furthermore, CMODH_VV also performs well in wind speed retrieval from GF3-02 SAR VV polarization data. In conclusion, the retrieval results have high precision, which preliminarily verified that GF3-02 SAR has high spatial resolution sea surface wind speed retrieval capability. In addition, the retrieval results show that the GF3-02 Satellite SAR image produced by NSOAS has fine radiation accuracy and radiation stability. Future work will first focus on analyzing the denoising process of GF3-02 SAR cross-polarization to evaluate the performance of GF3-02 SAR cross-polarization to retrieve wind speed. In addition, we will collect more sea surface data of each model of GF3-02 SAR that match the buoy wind fields and reanalysis wind field data and improve the performance evaluation of GF3-02 SAR sea surface wind speed retrieval. Moreover, the GMF is further optimized to improve the operational capability of GF3-02 SAR wind field retrieval.  
Figure 10: Comparison of NDBC buoy wind field and HY-2B SCA wind field. **(a)** Wind speed comparison results; **(b)** wind direction comparison results.  
Figure 9: Comparison of NDBC buoy wind field and ERA5 wind field. **(a)** Wind speed comparison results; **(b)** wind direction comparison results.  
**Author Contributions:** Conceptualization, J.Y. and B.H.; methodology, J.Y., B.H. and X.W.; software, J.Y. and L.Z.; validation, J.Y. and X.Y.; formal analysis, J.Y.; investigation, X.W.; data curation, J.Y., L.Z. and X.Y.; writing--original draft preparation, J.Y.; writing--review and editing, J.Y. and B.H.; supervision, Y.H. and C.D.; funding acquisition, B.H. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China under Grant Number 41976169.  
**Acknowledgments:** The GF3-02 SAR products are produced by the NSOAS, and the HY-2B SCA data is provided by the NSOAS through the website [[https://osdds.nsoas.org.cn/](https://osdds.nsoas.org.cn/)]([https://osdds.nsoas.org.cn/](https://osdds.nsoas.org.cn/)), accessed on 1 April 2022 (registration required). The authors thank ECMWF for freely providing the ERA5 wind data via [[https://cds.climate.copernicus.eu/](https://cds.climate.copernicus.eu/)]([https://cds.climate.copernicus.eu/](https://cds.climate.copernicus.eu/)), accessed on 16 February 2022. And we are also grateful for the wind measurements of buoy freely provided by NDBC via [[https://www.ndbc.noaa.gov/](https://www.ndbc.noaa.gov/)]([https://www.ndbc.noaa.gov/](https://www.ndbc.noaa.gov/)), accessed on 1 April 2022.  
**Conflicts of Interest:** The authors declare no conflict of interest.