Umov effect in single-scattering dust particles: effect of irregular shape.

The Umov effect manifests itself as an inverse correlation between the light-scattering maximum of positive polarization P_max and the geometric albedo A of the target. In logarithmic scales, P_max is linearly dependent on A. This effect has been long known in the optics of particulate surfaces and, recently, it was extended for the case of single-scattering dust particles whose size is comparable to the wavelength of the incident light. In this work, we investigate the effect of irregular shape on the Umov effect in single-scattering particles. Using the discrete dipole approximation (DDA), we model light scattering by two different types of irregularly shaped particles. Despite significant differences in their morphology, both types of particles reveal remarkably similar diagrams of log(P_max) versus log(A). Moreover, in a power-law size distribution r^-n with n=2.5-3.0, the Umov diagrams in both types of particles nearly coincide. This suggests little dependence on the shape of target particles in the retrieval of their reflectance using the Umov effect.