Simplified Earth infrared and albedo coefficient models for spacecraft thermal analysis based on the CERES data products

Abstract

For Earth-orbiting spacecraft, infrared flux and albedo flux from the Earth surface have a major impact on their thermal behavior. Earth infrared flux, also known as Outgoing Longwave Radiation (OLR), and the albedo coefficient are often evaluated as a uniform value in the spacecraft thermal analysis. However, in reality, these values exhibit complex variation over area and time. In this study, we propose simplified models for describing the OLR and albedo coefficient distributions, based on the measurement-based dataset compiled by Clouds and the Earth’s Radiant Energy System (CERES) project. The model consists of spherical harmonics and trigonometric functions for representing the spatial distribution and temporal variation, respectively. The model parameters are calculated to minimize the root mean square error (RMSE) between the model and the CERES dataset. The constructed models are employed to calculate the infrared and albedo flux in various types of orbits. These results are then compared to the flux values calculated by using the CERES dataset. The evaluation demonstrates that the model represents the overall spatial and temporal trend of the infrared and albedo flux. Additionally, by incorporating RMSE between the model and CERES dataset as the model uncertainties, hot and cold environments can be formulated to account for the effect of the local variations of the OLR and albedo coefficient.