Computation of Irradiance Distribution Near the Lunar South Pole and Data Validation

Abstract

The lunar south pole has emerged as a focal point in deep space research in recent years and irradiance computation in this region, which elucidates spatial and temporal irradiance distribution, is vital for future exploration. The irradiance of both the directly illuminated areas and permanently shadowed regions (PSRs) fluctuates rapidly with changes in the solar vector. In addition to scattered solar radiation, earthshine also contributes to the illumination of the lunar surface and its effect warrants further investigation. In this article, we propose a model to calculate the spatial and temporal distribution of irradiance near the lunar south pole, incorporating topographic data and ephemeris, which accounts for direct sunlight, scattered solar illumination, and earthshine. The accuracy of irradiance distribution contributed by solar light is validated by the calibrated images captured by narrow-angle cameras equipped on the Lunar Reconnaissance Orbiter. Moreover, our algorithm shows that the earthshine illuminates certain regions within the PSRs, although the intensity is comparatively low relative to that of scattered solar radiation. Combined with the simulation and real-captured images, the abnormal reflectance of the Shackleton crater is confirmed. The irradiance distribution from 88$^{\circ }$s to 90$^{\circ }$s on the lunar surface, spanning the period from 30 June 2026 to 31 December 2026 at 4-h intervals is calculated, providing a valuable reference for future lunar exploration.