Reply on RC1

V Shcherbakov

doi:10.5194/amt-2021-312-ac1

Abstract

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 20âm and particle extinction coefficients Îµp between 0.06 and 1.0âkmâ1. The resolution was 5âm for high values of Îµp (up to 10.0âkmâ1). 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 1.0âmrad. The effect of the width of the RFOV was studied for values up to 50âmrad. 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 8âkm or higher, and the full RFOV is 1.0âmrad. As for the full RFOV of 0.25âmrad, the single-scattering approximation is acceptable; i.e. the multiple-scattering contribution to the lidar signal is lower than 5â% for aerosols (Îµpâ²1.0âkmâ1), water clouds (Îµpâ²0.5âkmâ1), and cirrus clouds (Îµpâ¤0.1âkmâ1). When the distance to a layer of particles is 1âkm, the single-scattering approximation is acceptable for aerosols and water clouds (Îµpâ²1.0âkmâ1, both RFOVâ=â0.25 and RFOVâ=â1âmrad). As for cirrus clouds, the effect of multiple scattering cannot be neglected even at such low distances when Îµpâ³0.5âkmâ1.

Highlights

30 It is well accepted that single-wavelength lidar signals from cloud or aerosol layers are affected by multiple scattering (MS) when the optical thickness is quite high or/and the distance to a layer is large
The majority of simulations for ground-based and airborne lidars were performed at two values of the receiver field-of-view (RFOV): 0.25 mrad and 1.0 mrad
The effect of the width of the RFOV was studied for the values up to 50 mrad

Summary

Introduction

30 It is well accepted that single-wavelength lidar signals from cloud or aerosol layers are affected by multiple scattering (MS) when the optical thickness is quite high or/and the distance to a layer is large (see, e.g., Winker and Poole, 1995; Bissonnette et al, 1995; Winker, 2003). 35 et al, 2010), which is “roughly two orders of magnitude larger than for ground-based or airborne lidars, due to the large distance from the atmosphere, allowing a much greater fraction of the multiply-scattered light to contribute to the return signal” (Winker, 2003). It follows from Monte-Carlo simulations of CALIOP signals that multiple scattering is of importance even though photon mean free paths are much larger than the footprint diameter, e.g., cirrus clouds or aerosol layers (see, e.g., Winker, 2003). A number of approximate models, i.e., non-Monte-Carlo approaches to simulate lidar signals in multiple scattering conditions

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