Antonio Garcia Munoz (ESA)

Radiative transfer in planetary atmospheres: A Pre-Conditioned Backward Monte Carlo algorithm
When Mar 05, 2015 from 02:00 PM to 03:00 PM
What
  • Special Seminar
  • Colloquium
Where MCC
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The interpretation of polarized radiation emerging from a planet atmosphere must rely on solutions to the vector radiative transfer equation (VRTE). Monte Carlo integration of the VRTE is a valuable approach for its flexible treatment of complex viewing and/or illumination geometries, and it can intuitively incorporate elaborate physics. In this talk, I will present a novel pre-conditioned backward Monte Carlo (PBMC) algorithm for solving the VRTE. As classical BMC methods, the PBMC algorithm builds the solution by simulating the photon trajectories from the detector towards the radiation source, i.e. in the reverse order of the actual photon displacements. The neglect of polarization in the sampling of photon propagation directions in classical BMC algorithms leads to unstable and biased solutions for conservative, optically thick, strongly polarizing media such as Rayleigh atmospheres. The numerical difficulty is avoided by pre-conditioning the scattering matrix with information from the scattering matrices of prior (in the BMC integration order) photon collisions. Pre-conditioning introduces a sense of history in the photon polarization states through the simulated trajectories. Since the convergence rate for MC integration is independent of the integral’s dimension, the scheme is a valuable option for estimating the disk-integrated signal of stellar radiation reflected from planets. Such a tool is relevant in the investigation of both exo- and solar system planet phase curves. Examples of ongoing work on the investigation of planet phase curves will be presented.