Empirical model of multiple-scattering effect on single-wavelength lidar data of aerosols and clouds

Abstract

We performed extensive Monte Carlo (MC) simulations of single-wavelength lidar signals from a plane-parallel homogeneous layer of atmospheric particles and developed an empirical model to account for the multiple scattering in the lidar signals. The simulations have taken into consideration four types of lidar configurations (the ground based, the airborne, the CALIOP, and the ATLID) and four types of particles (coarse aerosol, water cloud, jet-stream cirrus, and cirrus). Most of the simulations were performed with a spatial resolution 20gm and particle extinction coefficients ϵp between 0.06 and 1.0gkm-1. The resolution was 5gm for high values of ϵp (up to 10.0gkm-1). The majority of simulations for ground-based and airborne lidars were performed at two values of the receiver field of view (RFOV): 0.25 and 1.0gmrad. The effect of the width of the RFOV was studied for values up to 50gmrad. The proposed empirical model is a function that has only three free parameters and approximates the multiple-scattering relative contribution to lidar signals. It is demonstrated that the empirical model has very good quality of MC data fitting for all considered cases. Special attention was given to the usual operational conditions, i.e. low distances to a layer of partices, small optical depths, and quite narrow receiver fields of view. It is demonstrated that multiple-scattering effects cannot be neglected when the distance to a layer of particles is about 8gkm or higher, and the full RFOV is 1.0gmrad. As for the full RFOV of 0.25gmrad, the single-scattering approximation is acceptable; i.e. the multiple-scattering contribution to the lidar signal is lower than 5g% for aerosols (ϵpĝ‰21.0gkm-1), water clouds (ϵpĝ‰20.5gkm-1), and cirrus clouds (ϵp≤0.1gkm-1). When the distance to a layer of particles is 1gkm, the single-scattering approximation is acceptable for aerosols and water clouds (ϵpĝ‰21.0gkm-1, both RFOVgCombining double low lineg0.25 and RFOVgCombining double low lineg1gmrad). As for cirrus clouds, the effect of multiple scattering cannot be neglected even at such low distances when ϵpĝ‰30.5gkm-1.