  The dust in protoplanetary disks is an important ingredient in planet
formation and can be investigated with model simulations and quantitative
imaging polarimetry of the scattered stellar light. This study explores
circumstellar disks with calculations for the intensity and polarization of the
reflected light. The photon scattering and absorption by the disk are
calculated with a Monte Carlo method for a grid of simple, rotationally
symmetric models approximated at each point by a plane-parallel dusty
atmosphere. The results of our simple disk models reproduce well the
measurements for the intensity $I/I_{\star}$, azimuthal polarization
$Q_{\varphi}/I_{\star}$, and fractional polarization $p_{\varphi}$ reported for
well-observed transition disks. They describe the dependencies of the scattered
radiation on the disk geometry and the dust scattering parameters in detail.
Particularly strong constraints on disk properties can be obtained from certain
diagnostic quantities. Therefore, they can be used as a diagnostic tool for the
analysis of quantitative measurements, specifically in constraining or even
determining the scattering properties of the dust particles in disks.
Collecting and comparing such information for many systems is required to
understand the nature of the scattering dust in planet-forming disks.
