  We investigate the intensity and polarization of reflected light from
planetary atmospheres. We present a large grid of Monte Carlo simulations for
planets with Rayleigh scattering atmospheres. We discuss the disk-integrated
polarization for phase angles typical of extrasolar planet observations and for
the limb polarization effect observable for solar system objects near
opposition. The main parameters investigated are single scattering albedo,
optical depth of the scattering layer, and albedo of an underlying Lambert
surface for a homogeneous Rayleigh scattering atmosphere. We also investigate
atmospheres with isotropic scattering and forward scattering aerosol particles,
as well as models with two scattering layers.
  The model grid provides a tool for extracting quantitative results from
polarimetric measurements of planetary atmospheres from solar system planets
and extrasolar planets, in particular on the scattering properties and
stratification of particles in the highest atmosphere layers.
Spectropolarimetry of solar system planets offers complementary information to
spectroscopy and polarization flux colors can be used for a first
characterization of exoplanet atmospheres. From limb polarization measurements,
one can set constraints on the polarization at large phase angles.
