EFFECTS OF EARTH ALBEDO ON THE LAGEOS-I SATELLITE

For several pears, 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 s hown to give acceleration peaks comparable to those observed. The effe cts of Earth albedo on LAGEOS I have been studied for the period March 1985 to June 1989, during which time measurements of reflected radiat ion from the Earth were made by one to three Earth Radiation Budget Ex periment (ERBE) satellites. Data taken during this experiment were pro cessed into hourly radiation exitances for the entire Earth divided in to 2.5 degrees x 2.5 degrees blocks. These ERBE data were used, along with detailed models of reflectance characteristics of the Earth, to c alculate the accelerations which reflected radiation would induce on L AGEOS I. The along-track component of the acceleration was averaged ov er 10 revolutions in order to average out the short-period effects. Th e results showed that the albedo effect on along-track acceleration di d not exceed 0.5 pm/s(2), or about 20% of the anomalous acceleration. Even this acceleration showed no correlation in phase with the observe d acceleration. The albedo accelerations were also used to calculate t he effects on the LAGEOS Keplerian orbital elements. The effects on th e LAGEOS node and inclination excitations were significant, having amp litudes of several milliarc seconds (mas) per year. The largest effect s were found to be on the eccentricity excitation function, having amp litudes at the 50-100 mas/yr level. The patterns also correlate well w ith the observed eccentricity vector excitations, but with a differenc e in sign, suggesting that some parameters estimated with LAGEOS data, such as ocean tide parameters, may have been corrupted by albedo effe cts.