Characteristics of light scattering at small phase angles by surfaces consisting of spherical particles

We present the results of measurements of the phase dependences of brightne ss and of the polarization and depolarization characteristics for surfaces consisting of spherical glass particles in the phase-angle range from 0.1 d egrees to 5.0 degrees. The measurements are performed using the laboratory photometer/polarimeter of Kharkov Astronomical Observatory and the photomet er of Jet Propulsion Laboratory. An optically thick layer of transparent-gl ass spheres with mean size of about 57 mum and refractive index of 1.44 exh ibits a strong opposition effect due to single scattering. The contribution of interparticle scattering is nearly independent of the phase angle. At a n angle of 0.4 degrees, the spheres exhibit a glory ring that manifests its elf in the phase behavior of all characteristics investigated. Small detail s are seen on the curves when a monochromatic radiation source is used for measurements. Their occurrence is confirmed by calculations based on the Mi e theory. The unusual behavior of the phase dependences of reflectivity, de gree of polarization, and color index for layers composed of spherical part icles can be used to search for sites of possible deposits of spherical gla ss (or ice) particles in regoliths of atmosphereless celestial bodies.