Impact of Atmospheric Delay on Equivalence Principle Tests Using Lunar Laser Ranging

Lunar laser ranging (LLR) has currently achieved millimeter-level ranging accuracy, establishing itself as a powerful tool for testing general relativity, particularly the equivalence principle. However, atmospheric delay introduces spurious signals in LLR-based equivalence principle tests, significantly degrading parameter constraint precision. Through analysis of observational data from the Grasse station—which has contributed the most normal point data in recent years—we demonstrate that atmospheric delay may significantly affect the test of equivalence principle. Moreover, this paper provides a comprehensive analysis of how temporal and elevation-angle non-uniformity in atmospheric delay distribution affects equivalence principle tests. Simulation results demonstrate that fixing the elevation angle significantly enhances the precision of equivalence principle tests. Therefore, to achieve more stringent constraints, it is recommended to analyze segments from the long-term ranging archive that have minimal variation in elevation angle.