A method to calculate Stokes parameters and angle of polarization of skylight from polarized CIMEL sun/sky radiometers

- The CE318-DP polarized measurements are not yet widely used except DoLP.
- Compared with DoLP and I, difficulty in calculating Stokes Q and U is discussed.
- A new polarized almucantar observation geometry based on CE318-DP is executed.
- We derive Stokes Q, U, and AoP both in principal and almucantar plane geometries.
- The results are comparable with previous DoLP and I, as well as model simulations.

The polarized CIMEL sun/sky radiometers have been routinely operated within the Sun/sky-radiometer Observation NETwork (SONET) in China and some sites of the AErosol RObotic NETwork (AERONET) around the world. However, the polarization measurements are not yet widely used due to in a certain degree the lack of Stokes parameters derived directly from these polarization measurements. Meanwhile, it have been shown that retrievals of several microphysical properties of aerosol particles can be significantly improved by using degree of linear polarization (DoLP) measurements of polarized CIMEL sun/sky radiometers (CE318-DP). The Stokes parameters Q and U, as well as angle of polarization (AoP) contain additional information about linear polarization and its orientation. A method to calculate Stokes parameters Q, U, and AoP from CE318-DP polarized skylight measurements is introduced in this study. A new polarized almucantar geometry based on CE318-DP is measured to illustrate abundant variation features of these parameters. The polarization parameters calculated in this study are consistent with previous results of DoLP and I, and also comparable to vector radiative transfer simulations.