Polarimetric and photometric properties of the moon: Telescope observation and laboratory simulation 2. The positive polarization
This article is a sequel to Shkuratov et al. (1992, Icarus 95, 283-299). It considers the lunar positive polarization based on telescopic observations and laboratory measurements. Data obtained from point-by-point measurements as well as from images are used to study the Moon at phase angles near the polarization maximum. The first type of data shows that measurements corresponding to young craters deviate from the regression line of the log A-log P correlation ( A and P are the reflectance and polarization degree, respectively). Following the approach suggested by Shkuratov et al. (1980, Astron. Circ. 1112, 3), new images of the polarimetric anomaly parameter characterized by b = log A + a · log Pmax are obtained for the western part of the lunar disc. Young mare and highland craters show up. Some anomalies presumably can be identified as volcanic ash deposits. A new empirical relationship between b and particle size was established by laboratory measurements of the lunar samples supplied by the "Luna" space probes. This relationship as well as that presented by Geake and Dollfus (1986, Mon. Not. R. Astron. Soc. 218, 75) is not universal and should be used carefully. New parameters (width and asymmetry) of the positive polarization branch, δ = (α 1 - α 2) /α max and ∆ = (α max - α 1) /(α 2 - α max) , where α1 and α2 are the phase angles at which P = 0.7 · Pmax are introduced. From laboratory polarimetric measurements of artificial glasses and lunar samples, some correlations between these parameters and the particle size of the surface were established.