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K. Muinonen (Univ. Helsinki)
Coherent backscattering is a key physical mechanism contributing to the opposition effects observed for numerous asteroids and other airless solar system bodies. In a particulate medium like the regolith of an asteroid, the multiply scattering electromagnetic waves propagating in opposite directions along the same paths always interfere constructively at the backward direction whereas, in other directions, the interference varies between constructive and destructive, the net effect being a peak close to the backward direction. An efficient scalar Monte Carlo technique is presented for computing coherent backscattering and radiative transfer by particulate media. What is essential for the treatise of coherent backscattering, instead of collecting reflected (and transmitted) rays into bins of finite angular size, the scattered intensity is updated at all reflection (and transmission) angles at each individual scattering process. Theoretical modeling is offered for the narrow opposition effects of the asteroids (44) Nysa and (64) Angelina. A vector Monte Carlo technique including polarization is under preparation.