How well does the Rayleigh model describe the E-vector distribution of skylight in clear and cloudy conditions? A full-sky polarimetric study

摘要

We present the first high-resolution maps of Rayleigh behavior in clear and cloudy sky conditions measured by full-sky imaging polarimetry at the wavelengths of 650 nm (red), 550 nm (green), and 450 nm (blue) versus the solar elevation angle θ_(s). Our maps display those celestial areas at which the deviation Δα=|α_(meas)-α_(Rayleigh)| is below the threshold α_(thres)=5°, where α_(meas) is the angle of polarization of skylight measured by full-sky imaging polarimetry, and α_(Rayleigh) is the celestial angle of polarization calculated on the basis of the single-scattering Rayleigh model. From these maps we derived the proportion r of the full sky for which the single-scattering Rayleigh model describes well (with an accuracy of Δα=5°) the E-vector alignment of skylight. Depending on θ_(s), r is high for clear skies, especially for low solar elevations (40%