  Light transfer in gradient-index media generally follows curved ray
trajectories, which will cause light beam to converge or diverge during
transfer and induce the rotation of polarization ellipse even when the medium
is transparent. Furthermore, the combined process of scattering and transfer
along curved ray path makes the problem more complex. In this paper, a Monte
Carlo method is presented to simulate polarized radiative transfer in
gradient-index media that only support planar ray trajectories. The ray
equation is solved to the second order to address the effect induced by curved
ray trajectories. Three types of test cases are presented to verify the
performance of the method, which include transparent medium, Mie scattering
medium with assumed gradient index distribution, and Rayleigh scattering with
realistic atmosphere refractive index profile. It is demonstrated that the
atmospheric refraction has significant effect for long distance polarized light
transfer.
