Abstract
The visible and NIR maximum degree of polarization (DoP) of cloud-free skylight depends on many factors, including wavelength, sun zenith angle, surface reflectance, and aerosol properties. For clear-sky environments, radiative transfer models accurately estimate the sky DoP when each of these properties is well constrained. (The model used here was recently compared with full-sky polarization measurements with excellent agreement.) Using coincident Hyperion satellite observations and AERONET retrievals to provide model inputs, we simulate the maximum sky DoP for a variety of locations. Results show large variations in the wavelength dependence of sky polarization across different Earth environments. Therefore, accurate modeling of the sky DoP depends largely upon proper representation of the surface and aerosols in the model. Simple models which do not incorporate accurate aerosol and surface information have limited utility for simulating cloud-free sky DoP.
Highlights
The degree of polarization (DoP) of skylight depends upon atmospheric aerosols, molecules, surface reflectance, and solar elevation angle
Given the excellent agreement between measurements and model results found in that study, in this paper we rely on the model to demonstrate the high variability of sky polarization spectra
Using the Stokes parameters simulated by the model, the maximum DoP in the principal plane was found for each case
Summary
The degree of polarization (DoP) of skylight depends upon atmospheric aerosols, molecules, surface reflectance, and solar elevation angle. Accounting for each of these properties can be complex, and an investigator may have limited observational data. In these situations, it can be preferable to make assumptions regarding some properties. While solar elevation angle and atmospheric molecular properties are calculated or derived from standardized models, aerosol and surface data must be measured from ground or satellite-based instruments. The results are constrained to realistic situations where both aerosol and high-spectral-resolution surface reflectance measurements are simultaneously available. These model results demonstrate the wide variety of sky maximum DoP values that are exhibited for cloud-free Earth environments across visible/NIR wavelengths. We have modified the code slightly to be able to directly incorporate parameters from the modified Rahman-Pinty-Verstraete (MRPV) surface bi-reflectance (BRF) model [6,7] used by the Multi-angle Imaging SpectroRadiometer (MISR) [8]
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