Can the Earth–Moon distance influence the accuracy of lunar irradiance with the plane-parallel assumption in atmospheric radiative transfer at night?

Abstract

AbstractThe plane-parallel atmosphere as an underlying assumption in physics is appropriately used in the rigorous numerical simulation of the atmospheric radiative transfer model (RTM) with incident solar light. The Solar irradiance is a constant with the plane-parallel assumption, which is attributed to the small difference in the distance between any point on the Earth’s surface to the Sun. However, at night, atmospheric RTMs use the Moon as a unique incident light source in the sky. The Earth–Moon distance is approximately 1/400 of the Earth–Sun distance. Thus, the varying Earth–Moon distance on the Earth’s surface can influence the top of atmosphere (TOA) lunar irradiance for the plane-parallel atmosphere assumption. In this investigation, we observe that the maximum biases in Earth–Moon distance and day/night band lunar irradiance at the TOA are ±1.7% and ±3.3%, respectively, with the plane-parallel assumption. According to our calculations, this bias effect on the Earth–Moon distance and lunar irradiance shows a noticeable spatio-temporal variation on a global scale that can impact the computational accuracy of an RTM at night. In addition, we also developed a fast and portable correction algorithm for the Earth–Moon distance within a maximum bias of 18 km or ±0.05%, because of the relatively low computational efficiency and the large storage space necessary for the standard ephemeris computational software. This novel correction algorithm can be easily used or integrated into the atmospheric RTM at night.