The Influence of Anisotropic Surface Reflection on Earth’s Outgoing Shortwave Radiance in the Lunar Direction

Abstract

The variation in the radiation budget at Earth’s top of the atmosphere (TOA) represents the most fundamental metric defining the status of global climate change. The accurate estimation of Earth’s shortwave radiant exitance is of critical importance to study Earth’s radiation budget (ERB) at TOA. Measuring Earth’s outgoing shortwave radiance (OSR) is a key point to estimate Earth’s shortwave radiant exitance. Compared with space-borne satellite systems, Moon-based sensors (MS) could provide large-scale, continuous, and long-term data for Earth radiation observations, bringing a new perspective on ERB. However, the factors affecting the estimation of Earth’s OSR in the lunar direction have not yet been fully explored, for example, anisotropic surface reflection and the effects of clouds and aerosols on radiation budget. In this work, we only focused on the influence of anisotropic surface reflection. To evaluate the extent of this influence, we constructed a model to estimate Earth’s OSR in the lunar direction (EOSRiLD), integrating the variables of anisotropic surface reflection (scene types, solar zenith angles, viewing zenith angles, and relative azimuth angles) and radiant flux in Moon-viewed sunlit regions. Then, we discussed it over three time periods (Earth’s rotation, revolution period, and synodic month cycle) and analyzed the impact of three variables (area of the Moon-viewed sunlit region, scene types, and incident-viewing angular bins) on anisotropic EOSRiLD. Our results indicate that EOSRiLD based on the assumptions of anisotropic and isotropic reflection is different but they all show the same monthly cycle change, which is related to the area of the Moon-viewed sunlit region. At the beginning and end of the lunar month, the differences between anisotropy and isotropy are greatest in each cycle; when it is close to the first half of each cycle, there is a small difference peak. Both anisotropy and isotropy are caused by the relative azimuth angles between the Sun and Moon. In conclusion, even if the Moon-based platform has a wider scope than space-borne satellites, the difference is still large between anisotropy and isotropy. Therefore, we still need to consider the anisotropic surface reflection based on the Moon-based observation.

Disk‐Integrated Earth’s Outgoing Longwave Radiation Viewed From a Moon‐Based Platform: Model Simulations

“…Recently, serving the Moon as an Earth observation platform has gained widespread attentions from the remote sensing community (Carruthers & Page, 1972; Gorkavyi et al., 2021; Guo et al., 2016, 2017; He et al., 2013, 2016; Moccia and Renga, 2010; Pallé and Goode, 2009; Song et al., 2017; Xu and Chen, 2019; Xu et al., 2020). Earth’s emitted radiation, that is, Earth’s outgoing longwave radiation (OLR), is one of the potential observed parameters (Guo et al., 2017; Huang et al., 2022; Pallé and Goode, 2009; Song et al., 2017; Wu et al., 2022; Ye et al., 2021; Zhang et al., 2022). Determining the disk‐integrated Earth’s OLR is of importance in probing the characteristics of Earth’s emitted radiation, and in estimating the global mean OLR.…”

Lunar calibration for the visible light channel of FY-2F satellite

“…Fewer domestic geostationary meteorological satellites use lunar targets for radiometric calibration work. Rong-Hua Wu7 et al used the MERSI cold space observation lunar data carried on the FY-3C satellite to obtain the radiometric attenuation of the MERSI instrument of FY-3C by using the method of ratio with the stable channel. The geostationary satellite Fengyun-2 series of satellites cannot observe the Lunar in a planned manner, but using the incidental Lunar image in the operational image of the Earth's full disk, Chen Fuchun et al8…”