Effects of Earth albedo on the LAGEOS I satellite

Abstract

For several years, Earth albedo has been one of the leading candidates for explaining the anomalous along‐track acceleration experienced by the LAGEOS satellites, with reasonable reflection models having been shown to give acceleration peaks comparable to those observed. The effects of Earth albedo on LAGEOS I have been studied for the period March 1985 to June 1989, during which time measurements of reflected radiation from the Earth were made by one to three Earth Radiation Budget Experiment /ERBE) satellites. Data taken during this experiment were processed into hourly radiation exitances for the entire Earth divided into 2.5° × 2.5° blocks. These ERBE data were used, along with detailed models of reflectance characteristics of the Earth, to calculate the accelerations which reflected radiation would induce on LAGEOS I. The along‐track component of the acceleration was averaged over 10 revolutions in order to average out the short‐period effects. The results showed that the albedo effect on along‐track acceleration did not exceed 0.5 pm/s2, or about 20% of the anomalous acceleration. Even this acceleration showed no correlation in phase with the observed acceleration. The albedo accelerations were also used to calculate the effects on the LAGEOS Keplerian orbital elements. The effects on the LAGEOS node and inclination excitations were significant, having amplitudes of several milliarc seconds /mas) per year. The largest effects were found to be on the eccentricity excitation function, having amplitudes at the 50–100 mas/yr level. The patterns also correlate well with the observed eccentricity vector excitations, but with a difference in sign, suggesting that some parameters estimated with LAGEOS data, such as ocean tide parameters, may have been corrupted by albedo effects.