Shkuratov et al., 2004

Laboratory and computer modeling investigations of the negative polarization of particulate surfaces at small phase angles are important in the development of remote-sensing research of atmosphereless celestial bodies. We present measurements of the phase-angle dependence of the intensity and degree of linear polarization of particles in air and particulate surfaces composed of the particles at illuminating wavelengths 0.63 and and 0.44 um.
The particulate surface measurements were carried out with the equipment at the Kharkov National University; whereas the scattering measurements of single particles were carried out with the Amsterdam equipment. We study a suite of samples of natural mineral particles (including two volcanic ash samples) that are characterized by a variety of shapes and colors. We find evidence that suggests that in some instances the negative polarization of the surfaces is a remnant of the negative polarization of the single scattering by particles constituting the surfaces. Computer simulations of the light scattering from the particulate surfaces support this conclusion.