## 5 Conclusions  
The VIIRS DNB on Suomi NPP and NOAA-20 have great sensitivity to low light radiances, which allows us to measure lunar radiances reflected by the deep convective clouds from full moon to quarter moon on a monthly basis with no significant temporal gap. It has been shown that the DNB calibration is very stable during day time over deep convective clouds with reflected solar radiances, and it is expected that the night time DNB calibration stability is also comparable based on analysis of calibration data.  
This study shows that the VIIRS DNB measured lunar radiances reflected from deep convective clouds is primarily a function of lunar phase angle and lunar zenith angle. There is good consistency in the DNB observations between NOAA20 and Suomi NPP, although a bias on the order of up to 5% is found between them, with the NOAA20 DNB biased lower. The Suomi NPP VIIRS DNB observations matched very well with the lunar model predictions by GIRO within 3% with a standard deviation of  
Figure 10: Comparison between GIRO and MT2009 Lunar Irradiance Model Outputs for the November-December 2018 lunar cycle.  
\(\pm\)5% (1\(\sigma\)) based on analysis of data from October 2018 to March 2019, which significantly outperforms the VIIRS DNB instrument specification. The two lunar irradiance model outputs are found to agree within \(\pm\)7% for a large range of lunar phase angles, although the difference can be up to 17% at high lunar phase angles at low radiances. The GIRO was unable to produce predictions for near full moon cases, where VIIRS DNB observations are available occasionally. The unique dataset and methodology presented in this paper provide a viable technique for evaluating and ensuring the consistency of VIIRS DNB calibration across satellites for low light observations. It also potentially provides an independent approach validating both the lunar irradiance and ADM bi-directional reflectance models for improved accuracy, as well as ensuring our confidence in their use for satellite radiometer calibration.  
[PERSON] conceived of and designed the study, analyzed the data, and wrote the paper; [PERSON], [PERSON], and [PERSON] supported the study with data acquisition, processing, model prediction, and analysis, as well as graphic drawing.  
This study is partially funded by the NOAA Joint Polar Satellite System (JPSS) Program with a grant to the University of Maryland.  
The authors would like to thank EUMETSAT for providing the GIRO model (version 1.0) for lunar irradiance predictions. We thank Dr. [PERSON] for his orbital dynamics analysis which helped us clarify related issues in this study. We also thank Dr. [PERSON], Mr. [PERSON], and Dr. [PERSON] for clarifying several issues related to the operational calibration of VIIRS DNB. Special thanks go to Dr. [PERSON] for her extensive editorial assistance and proofing reading the manuscript. Thanks are extended to the anonymous reviewers for their thorough review and constructive suggestions and comments. The manuscript contents are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of NOAA or the U.S. government.  
The authors declare no conflict of interest.