Small angle approximation for the lidar return from clouds and fogs

Abstract

The paper is aimed at the inter-comparison of the small angle approximation (SAA) for the lidar return with Monte Carlo calculations at small receiver field of views, where the SAA can be used for the evaluation of lidar signals from clouds and fogs. The diffraction component of light scattering by a local volume of a cloudy medium is fully taken into account and the geometrical part of light scattering field has been neglected. It has been found that the derived approximation provides useful approximation for the simulation of lidar signals from a cloudy medium close to its boundary, where the contribution of small-angle light scattering and propagation on the path from the cloud boundary to the observation point and back is significant. It has been found that the multiple light scattering enhancement factor A in the framework of the SSA for clouds with the same half - width parameter μ of the droplet size distribution depends just on two main parameters: optical depth τand the scale parameter s, which is equal to the ratio of the effective scattering angle to the receiver field of view.