The impact of surface roughness on scattering by realistically shaped wavelength-scale dust particles

The impact of dust particles surface roughness on scattering is investigated using model particles with realistic shapes based on stereogrammetry, up to size parameter 10. The surface roughness is introduced at the particle surfaces by randomly adding or subtracting volume elements in random surface locations with a Monte Carlo method, in such a way that the total number of volume elements comprising the particle is approximately conserved. Assuming an ensemble of randomly oriented particles, roughening seems to decrease the backscattered intensity, reduce the horizontal and vertical polarization, especially in the backscattering hemisphere, and increase diagonal and circular polarization at all scattering angles. The asymmetry parameter and single-scattering albedo are virtually unaffected, while lidar ratio and linear depolarization ratio are increased significantly, especially for large size parameters. These results are qualitatively similar for all particles and the impact of roughness on scattering is clearly related to the amount of roughening. (C) 2014 Elsevier Ltd. All rights reserved.