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
(Vokrouhlick\'y \& 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.
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