# FY3E GNOS II GNSS Reflectometry: Mission Review and First Results
## 5 Summary and Future Perspectives  
The GNOS II on FY3E is the first GNSS-R payload on an operational Chinese meteorological satellite. It successfully integrates GNSS RO and GNSS-R in one instrument, receiving signals from multiple GNSS constellations, such as GPS and BeiDou. This paper introduced the instrument, GNSS-R measurements, data product, power calibration and wind speed retrieval algorithm of GNOS II. Preliminary validation for Level 2 wind speed data in its in-orbit testing stage was presented. For data with RCG larger than 15 and SNR larger than \(-3\) dB, the overall root-mean-square error of retrieved wind speeds was 1.78 m/s for reflections from GPS and 1.70 m/s for reflections from BDS at wind speeds below 20 m/s.  
The wind speeds in this paper were retrieved from the GMFs developed from pre-launch simulated data. The next step is to update the GMFs using the real measurements. In addition, the estimation of GNSS transmitter EIRP and the quality control scheme should be refined. Since the wind validation in this paper is preliminary, a comprehensive assessment of the wind speeds retrieved using buoy winds, model winds and other satellite observations (such as scatterometer winds) is expected in the future. In addition, products related to land and the cryosphere, such as soil moisture and sea ice coverage, are currently on the way. In the future, the FY satellite series (including FY3F, FY3R, FY3G, etc.) will all carry GNOS II to establish a GNSS-R observation constellation. The constellation of GNSS observatories will provide larger spatial coverage and higher temporal resolution for Earth observations.  
Conceptualization, G.Y., W.B., J.W., P.Z., X.H. and Y.S.; methodology, G.Y., W.B., Y.S., Q.D., X.W. and Y.C.; software, J.X., F.H., C.Y., X.M., G.T., P.H. and C.L.; data curation, J.X., F.H. and C.Y.; writing--original draft preparation, G.Y., W.B., F.H., J.X. and C.Y.; writing--review and editing, J.W., P.Z., G.Y. and W.B.; project administration, G.Y., J.W., P.Z., Y.S., X.H., N.X., X.Z. and X.X.; funding acquisition, J.W., P.Z. and X.H. All authors have read and agreed to the published version of the manuscript.  
This work is supported by National Natural Science Foundation of China (41774195), the Ten-thousand Talents Program of [PERSON] and in part by the National Natural Science Foundation of China under grant 42074042 and 42104032 and in part by the Youth Cross Team Scientific Research Project of the Chinese Academy of Sciences (JCTD-2021-10) and in part by the Feng Yun 3 (FY-3) Global Navigation Satellite System Occultation Sounder (GNOS and GNOS II) Development and Manufacture Project led by the National Space Science Center, Chinese Academy of Sciences (NSSC/CAS). This work is also supported by Special Fund for Public Welfare Industry (meteorology) (GYHY201306063).  
The ECMWF ERA5 reanalysis is available at: [[https://cds.climate.copernicus.eu](https://cds.climate.copernicus.eu)]([https://cds.climate.copernicus.eu](https://cds.climate.copernicus.eu)) (accessed 11 November 2021).  
Figure 14: Scatter density plots for the comparison between GNOS II Level 2 wind speeds and collocated ECMWF wind speeds. The left one is for results from GPS signals and the right one is for results from BDS signals.  
**Acknowledgments:** The authors would like to acknowledge Copernicus Climate Change Service for providing the ECMWF ERA5 reanalysis data.  
**Conflicts of Interest:** The authors declare no conflict of interest.