A Hierarchical Spherical Algorithm Over the Triangular Domain for Lunar Regional Brightness Temperature Analysis

The regional analysis of lunar brightness temperature (TB) data by the microwave radiometer (MRM) onboard the Chang’E-2 (CE-2) lunar probe holds significant importance in the field of thermal characteristics and TB distribution. However, most existing methods rely on a 2-D conversion, which makes it challenging to represent spherical TB data directly due to the nondevelopability of the sphere. Inspired by the triangular domain, we propose a hierarchical spherical algorithm for lunar regional TB analysis, which embeds the spherical triangular domain into the interpolation. First, we construct an octahedral framework based on spherical area coordinates (SACs), which obtain spherical information over the triangular domain by establishing coordinate correlation to enhance the feature representation ability of TB data. Second, we propose a spherical triangulation approach to reduce the loss of detailed TB information in the lunar regions. Finally, the hierarchical spherical algorithm refines the spherical triangular lattices from coarse to fine in the lunar regions. It integrates all the spherical TB functions from each level of the hierarchy into the 3-D features on the sphere, minimizing the result errors. The experimental results suggest that the hierarchical spherical algorithm for lunar regional TB construction has competitive performance and outperforms several representative methods. Extensive experiments are carried out to analyze the diurnal TB variations in typical regions, i.e., the Copernicus, Tycho, Aristarchus, and Stevinus.