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We compare the transport theoretic and a stochastic approach of modeling light propagation in the atmosphere. Computations of LIDAR return signals using algorithms based on the two different approaches show very good agreement of the numerical data. Furthermore, a deeper analysis of the formulas for the LIDAR return signal obtained from two kinds of modeling shows that they are equivalent. Combining these approaches and introducing splitting techniques, variance reduction Monte Carlo methods and codes are designed which are adapted to the configuration of the LIDAR. These codes allow the calculation of multiple scattering effects with high accuracy. Finally, we point out the importance and some perspectives of ultilization of multiple scattering in laser remote sensing of clouds.

The contribution of multiple scattering to a spaceborne lidar return from clear molecular atmosphere obscured by transparent upper-level crystal clouds is assessed by the use of the variance-reduction Monte Carlo technique. High anisotropy of scattering in the forward direction by polydispersions of ice crystals is the basis of a significant effect of multiple scattering for small values of the lidar receiver field of view. Because of scattering by large nonspherical crystal particles, the lidar signal backscattered from the molecular atmosphere under the cloud increases significantly compared with the single-scattering return. The ratio of the multiple-to-single-scattering contributions from the clear atmosphere hidden by the clouds is greater than from the crystal clouds themselves, and it is proportional to the values of cloud optical thickness.