The perturbations of earth penumbra on LAGEOS II perigee and the measurement of lense-thirring gravitomagnetic effect

In the last few years the attenuation and deflection of the solar radiation through the atmosphere has been deeply investigated. The proposed model combines both the geometric and physical causes of penumbra. The physical effects induced by the atmosphere on the solar radiation are treated by a purely empirical approach. The idea is to use the atmospheric data of extinction and deflection of star-light which are usually collected during an astro-photometric calibration. In the last years it was performed for the first time the measurement of the Lense-Thirring gravitomagnetic (L-T) effect using a combination of some orbital parameters of both LAGEOS satellites currently in orbit. The parameters involved in the combination were: the node of the LAGEOS I, the node and perigee of the II. The assessment of the effects of non-gravitational perturbations on the LAGEOS II perigee has been the most critical and intriguing challenge to perform such measurement. So in the present work the model of penumbra is applied to the perigee of LAGEOS II in order to deeply understand what is its contribution to the overall uncertainty in the L-T LAGEOS experiment. (C) 1999 COSPAR. Published by Elsevier Science Ltd.