## 5 Conclusions  
A MERO could bring several improvements to current ERB observations: (1) long-term continuous observation in a diurnal cycle for a region on Earth (12-h continuous observation per day) enables a MERO to capture the small-temporal-scale variations of the TOA OLR and OSR, benefiting the production of a more accurate measurement of OLR and OSR diurnal variations; (2) a MERO could simultaneously measure the half-globe TOA OSR and OLR fluxes at an acceptable spatial resolution; this could help to shed light on the regional and global radiation imbalance without the bias caused by non-simultaneous sampling of the spatial and temporal variability of TOA OSR and OLR; (3) all locations on the Moon share a highly similar viewing geometry towards Earth, facilitating the merging of data from MERO missions of different periods to produce long-term OSR and OLR data with good consistency; (4) a MERO could provide a longer-term observation within a diurnal cycle for polar regions compared to current LEO and GEO ERB missions.  
In this paper, we quantify the effects of the spatial resolution and sampling scheme on the measurement error for a Moon-Based Earth Radiation Observatory (MERO). It is found that the spatial sampling error in the unit of percentage reduces linearly as the spatial resolution varies from 1000 km to 100 km; the rate is 2.5%/100 km for the TOA OSR flux, which is higher than that (1%/100 km) for TOA OLR flux. Moreover, this rate becomes larger when the spatial resolution is less than 40 km. It is also shown that sampling temporal sequence with a starting time of 64 min and with a sampling interval of 90 min is the optimal sampling scheme that results in the least temporal sampling error for a MERO system with a 40 km spatial resolution; however, due to the \"real\" TOA OSR and OLR fluxes are based on the 1-h CERES data in this study, which neglect the actual data variability that is less than 1 h, this conclusion still can be improved by utilizing a more realistic TOA fluxes dataset in higher temporal resolution. The proposed method and the derived results in this study could help to determine the optimal spatial resolution and sampling scheme (sampling interval and the temporal sampling sequence) of a MERO system under specific manufacturing budget and measurement error limits.  
Conceptualization, W.D.; methodology, W.D. and J.L.; software, W.D., J.L. and Q.Y.; validation, H.R., Q.Y.; writing--original draft preparation, W.D.; writing--review and editing, W.D., J.L., Q.Y., H.R. and S.J.; visualization, W.D., S.J. and J.L.; project administration, S.J. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the Experiments for Space Exploration Program of the Qian Xuesen Laboratory, China Academy of Space Technology (Grant No. TKPSY-2020-06-02) and by the Startup Foundation for Introducing Talent of NUIST project at Nanjing University of Information Science and Technology (Grant No. 2019r086).  
The CERES SYN data are the basis of this study are publicly available on the CERES data archive at [[https://ceres.larc.nasa.gov/data/](https://ceres.larc.nasa.gov/data/)]([https://ceres.larc.nasa.gov/data/](https://ceres.larc.nasa.gov/data/)) (access on 12 February 2021).  
The authors declare no conflict of interest.