Optical Properties of Snow Surfaces: Multiangular Photometric and Polarimetric Hyperspectral Measurements

Understanding the optical properties of light reflected from snow surfaces is fundamental for remote sensing-based characterizations of snow properties and quantification of radiative transfer in the atmosphere-earth system. In theory, both intensity and polarization are required for describing the optical properties of light reflected from snow. However, thus far, a few studies have focused on the polarimetric properties of snow. In this study, we measured both multiangular photometric and polarimetric (based on the Stokes parameters) hyperspectral field results of snow with different properties (grain size, pollution levels, and microscopic surface roughness). By considering the absorption ratio of the polarizer, the intensity defined by photometric results [bidirectional reflectance factor (BRF) and hemispherical directional reflectance factor (HDRF)] was first confirmed to be similar to those derived from polarimetric measurements [I parameter reflectance factor (IpRF)] of snow surfaces. Then, the bidirectional polarized reflectance factor (BPRF) of snow, which is used to define the polarimetric properties of snow, was found to be useful for characterizing snow properties. Moreover, comparing ground measurements of snow BPRF with modeled results, we found that some existing BPRF models did not match well with the BPRF measured in the 2 pi space. These results suggest that more attention should be paid to the combination of IpRF (BRF or HDRF) and BPRF because polarimetric measurements can be used both for describing the optical properties of light reflected from snow and for quantifying snow properties.