The Influence of Atmospheric Composition on Polarization in the GEMS Spectral Region

摘要

Sunlight is unpolarized when it enters the Earth's atmosphere, and becomes polarized when interacting with atmospheric constituents. In the present study, the polarization state of ultraviolet-visible light in the spectral region (300-500 nm) of the Geostationary Environmental Monitoring Spectrometer (GEMS) is analyzed using the Vector Linearized Discrete Ordinate Radiative-Transfer (VLIDORT) model. The results indicate that the polarization characteristics of scattered solar light emerging from the atmosphere and observed in space vary with the amount of absorbing gases and aerosols, and with the presence or absence of clouds in the atmosphere. The degree of linear polarization (DOLP), which is related to the scattering angle of the light, is highly affected by the viewing geometry of the sun and satellite. Aerosols and clouds curtail the degree of polarization that is caused by Rayleigh scattering. The results of the model simulation for actual atmospheric conditions are assessed by comparing the Stokes fraction, i.e. the ratio of the linearly-polarized component to the total intensity, as observed from the polarization-measurement device (PMD) of the Global Ozone Monitoring Experiment-2 (GOME-2). The simulated Stokes fractions are found to be in very good agreement with the PMD observations for clear-sky regions, although some discrepancies are observed for regions with optically thin clouds.