Earth's Outgoing Radiation Monitoring From the Moon

Earth's outgoing radiation (EOR) at the top-of-atmosphere (TOA) is a vital parameter of earth's energy budget. Moon-based earth observations as one of the scientific goals of the International Lunar Research Station (ILRS) project could provide long-term, well-calibrated, and disk-integrated EOR data to complement existing platforms. To study the difference between a Moon-based platform and existing platforms, in this study, we established a method to simulate outgoing longwave (OLR) and shortwave radiation (OSR) from a Moon-based radiometer. Then, by parameterizing Moon-based earth observations, the relationship between observation geometry and diurnal and seasonal variations of OLR were derived. Finally, the relationship between OSR viewed from a Moon-based sensor and earth's phase is obtained. We summarized three Moon-based EOR observation characteristics. 1) Moon-based observational scope is almost earth's hemisphere, and Earth-Moon distance has great effects on EOR. With the Moon moves from perigee to apogee, the OLR decreases almost 40% and OSR decreases about 60%. 2) Diurnal and seasonal variations also influent OLR, and compared correlation coefficients between OLR removing the effects of seasonal with diurnal, the former has bigger value, meaning hemisphere-scale observations is less sensitive to seasonal signals. 3) A Moon-based platform can observe the earth with different earth's phases. For OLR, earth's phase changes earth's scene. For OSR, with the increase of earth's phase, OSR is greatly decreased, the ratio of incoming shortwave radiation (ISR) is close to earth albedo when the earth's phase is 0 degrees. Our results offer new understanding that will help to facilitate Moon-based monitoring of EOR.