Specular reflection of sunlight from wavy ocean surfaces and the albedo effect on satellite orbits. II. LAGEOS long-term albedo perturbations reassessed.
We reanalyse the role of radiation pressure by sunlight specularly reflected from the Earth's ocean surface in generating long-term perturbations on the orbit of the laser-tracked satellite LAGEOS, by using the new theory for light reflection from a "rough" (or "wavy") surface developed in the previous paper of this series (Vokrouhlicky & Farinella 1994a). The results of the more accurate method based on the application of geometrical optics to a distribution of surface elements with different orientations are compared to those based on a simple redefinition of the Fresnel reflection coefficient. In agreement with the estimates based on the dependence of the perturbing acceleration upon the satellite's mean anomaly, we show that the "roughness" of the ocean surface and the resulting finite-lobe reflection pattern cause a 10-40% decrease of the magnitude of the long-term perturbations of LAGEOS' semimajor axis with respect to the ideal, mirror-like reflection case. However, the resulting perturbations are still large enough that radiation pressure by specularly reflected sunlight provides a major contribution to the observed LAGEOS along-track residuals. We also confirm that the secular effect on the nodal longitude of LAGEOS does not exceed 1 milliarcsec/year, namely a few percent of the general-relativistic Lense-Thirring precession, and that long-periodic effects on the inclination can reach about 3 milliarcsec/year. In order to model in a reliable way all these effects, extensive data on the optical properties of ocean surfaces and the global cloud coverage would be required.
Astronomy and Astrophysics
- Pub Date:
- September 1995
- CELESTIAL MECHANICS;
- ARTIFICIAL SATELLITES;
- SPACE PROBES;
- RADIATION MECHANISMS: MISCELLANEOUS