# Precipitable Water Vapor Retrieval Based on DPC Onboard GaoFen-5 (02) Satellite
## 5 Conclusions  
The DPC is one of the main payloads on board the newly launched GFS-02 satellite. At present, the DPC is in the stage of on-orbit testing, and no publicly released DPC PWV data are available. In this study, we developed a DPC-suited water vapor retrieval algorithm based on the spectral characteristics of DPC data. The DPC water vapor retrieval algorithm consists of three parts: (1) the construction of the PWV retrieval lookup table, (2) the calculation of the WVAT in the DPC 910 nm band, and (3) DPC water vapor retrieval. The DPC PWV data are spatially continuous and can reflect the global water vapor content distribution. The validation results based on ground-based data show that the DPC PWV data developed in this study have metric values close to those of the widely used and accurate MODIS PWV data published by NASA. Although the DPC PWV data developed in this study have low absolute error and relative error, we still found a systematic overestimation trend in DPC PWV data. We found it was mainly caused by the calibration error. The DPC needs an updated calibration coefficient to further improve the accuracy of PWV products in the future.  
This work was carried out in collaboration with all the authors. Conceptualization, C.W., Z.S., Y.X., Z.L. D.L. and X.C.; Methodology, C.W., Z.S., Y.X. Z.L. and D.L.; Data acquisition, Z.S. and Y.X.; Supervision, Z.S. and Y.X.; Visualization, C.W., Z.S., Y.X. and D.L.; Validation; C.W. and Y.X.; Original draft preparation, C.W. and Y.X.; Writing--review and editing, Z.S., Y.X., Z.L., D.W. and X.C. All authors have read and agreed to the published version of the manuscript.  
This work was supported by National Key R&D Program of China (grant No. 2020 YFE0200700), National Natural Science Foundation of China (grant No. 42175147), and National Outstanding Youth Foundation of China (grant No. 41925019).  
The DPC data can be obtained from China Centre for Resources Satellite Data and Application (available online: [[http://www.cresda.com](http://www.cresda.com)]([http://www.cresda.com](http://www.cresda.com)) (accessed on 20 February 2022)).  
Figure 7: Comparison between DPC TOA reflectance in the 865 nm band and DPC TOA reflectance in the 910 nm band after water vapor absorption correction. The correction is implemented using 6 SV with AERONET PWV as input.  
The AERONET data can be downloaded from the official website of AERONET ([[https://aeronet.gsfc.nasa.gov/](https://aeronet.gsfc.nasa.gov/)]([https://aeronet.gsfc.nasa.gov/](https://aeronet.gsfc.nasa.gov/)), last accessed on 5 March 2022). The MODIS data can be downloaded from the official website of NASA ([[https://ladsweb.modaps.eosdis.nasa.gov/](https://ladsweb.modaps.eosdis.nasa.gov/)]([https://ladsweb.modaps.eosdis.nasa.gov/](https://ladsweb.modaps.eosdis.nasa.gov/)), last accessed on 25 February 2022).  
**Acknowledgments:** The authors thank [PERSON], [PERSON], and [PERSON] from China Centre for Resources Satellite Data and Application for providing DPC L1 data during the on-orbit testing of the Gaofen5-02 satellites. We would also like to thank the PI(s), Co-I(s), and their staff for their efforts in establishing and maintaining the AERONET sites for providing valuable validation datasets. In addition, we thank NASA for providing us with MODIS water vapor data.  
**Conflicts of Interest:** The authors declare no conflict of interest.