Simulation of Polarization Effects in UV-VIS Region by Using the Radiative Transfer Model for GEMS/GK-2B

The radiative transfer model for GEMS/GK-2B (Geostationary Environment Monitoring Spectrometer) can be used as a simulation tool in the development of data processing algorithms. For example, it could be used in the production of synthetic data required for validation or correction of the data processing algorithms.

GEMS RTM can be set to calculate normalized radiance for each component of Stokes parameter, using vector or scalar for a Rayleigh atmosphere with absorbing gases such as O₃, NO₂, SO₂, H₂CO, and O_4. Lorenz-Mie theory has been used to calculate the single scattering properties of clouds and aerosols such as emissivity, scattering, absorption, single scattering albedo and phase function.

The scalar mode brings out the difference up to 8% for the radiance in comparison with the vector mode. The absolute difference is largest when the solar zenith angle is 45 degree and the relative azimuth angle is 0 or 180 degree. And these differences are greatly influenced by the polarization effects of the ozone.

 In a given Rayleigh simulating condition, DOLP (Degree of Linear Polarization) is, on average, about 0.5 throughout the spectral region. From 0.3 to 0.5 , the DOLP tends to be somewhat weakened at longer wavelengths. The effect of NO₂ and O₄ as compared to other gases is relatively large, the polarization effect of O₄ is large compared with those of other absorbing gases. Furthermore, when aerosols are loaded in the atmosphere, DOCP (Degree of Circular Polarization) and ellipticity appear differently depending on the type of aerosols.