Degree of Linear Polarization of Land Surfaces: Analyses Using POLDER/PARASOL Measurements

Polarized reflectance (<inline-formula> <tex-math notation="LaTeX">$R_{\mathrm {p}}$ </tex-math></inline-formula>) and degree of linear polarization (DOLP) provide essential information about polarized characteristics of land surfaces. For a given target, DOLP determines the magnitude of <inline-formula> <tex-math notation="LaTeX">$R_{\mathrm {p}}$ </tex-math></inline-formula>. It has been proved that DOLP can be used for some remote monitoring cases that cannot be well detected with either non-polarized or polarized reflectance. Several bidirectional polarization distribution function (BPDF) models have been proposed in the last several decades to reproduce the angular distribution of <inline-formula> <tex-math notation="LaTeX">$R_{\mathrm {p}}$ </tex-math></inline-formula>, but much less attention has been devoted to modeling and analyzing of DOLP. In this study, the Nadal–Bréon BPDF model was transferred for calculating the DOLP of earth targets, and characteristics of DOLP were analyzed based on the modeling results. To evaluate the model’s feasibility, two experiments were executed: a fitting and a <italic>a priori</italic> modeling. The results showed good correlations (<inline-formula> <tex-math notation="LaTeX">$r>0.9$ </tex-math></inline-formula>) between estimated and measured DOLP when the model was fitted with POLDER/PARASOL (a space-borne multi-angle multi-spectral polarimetric sensor) measurements. An increase of accuracy from 490 nm to 865 nm for fitting modeling was achieved and the highest accuracy was found at 865 nm for both experiments, with overall relative root mean square errors of 1.1 and 1.3 for fitting and <italic>a priori</italic> modeling, respectively. Class-based free parameters can be used for the <italic>a priori</italic> model of DOLP. The dispersion of the target-based free parameters controls the correlation of the <italic>a priori</italic> modeling results. Moreover, the maximum DOLP was found to be strongly determined by the corresponding bidirectional reflectance factor for every surface type (<inline-formula> <tex-math notation="LaTeX">$R^{2}=0.86$ </tex-math></inline-formula>). This study provides an additional approach for obtaining DOLP from remote sensing platform and is helpful for studies of typical land surfaces.