Radiation pressure from sunlight reflected by the Earth's
surface and atmosphere affects in a detectable way the orbit of
laser--tracked Earth satellites or spacecraft carrying
microaccelerometric devices. In particular, long--term perturbations
arise as a consequence of radiation specularly reflected from ocean
surfaces. Most previous models of this effect modelled the ocean
surface as a perfectly smooth spherical mirror, such that the
reflected light beam was seen at the satellite as collimated and
coming from a specific point of the Earth's surface. We now improve
on these simplified models, taking into account that the wavy geometry
of the ocean surface results into a finite aperture of the reflected
light beam and into an extended (and non--uniform) image of the Sun
seen on the surface itself from the satellite's position. First we
use geometrical optics and a statistical description of the
orientation of small--scale reflecting surface elements to define an
averaged Fresnel--type reflection law giving the amount of reflected
radiation as a function of incidence angle. Then we compare the
results of two possible methods to derive the local radiative field at
the satellite: (i) using the averaged Fresnel reflection coefficient
but assuming again a perfectly spherical surface; (ii) analyzing in
detail the distribution of ray geometries from the whole surface
region contributing reflected sunlight, with the method outlined in
Vokrouhlick\'y \etal (1993c). The results show that the mirror--like
model in fact overestimates the perturbative effects of reflected
sunlight for LAGEOS--type satellites, although the extent of this
overestimate depends on the statistical properties of the ocean
surface geometry.
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