Ability of multiangle remote sensing observations to identify and distinguish mineral dust types : Optical models and retrievals of optically thick plumes : Quantifying the radiative and biogeochemical impacts of mineral dust

We present a systematic theoretical study of atmospheric mineral dust radiative properties, focusing on implications for multiangle and multispectral remote sensing. We model optical properties of complex, nonspherical mineral dust mixtures in three visible-near-infrared satellite channels: 0.550, 0.672, and 0.866 μm, accounting for recent field and laboratory data on mineral dust morphology and mineralogy. To model the optical properties of mineral dust, we employ the discrete dipole approximation technique for particles up to 2 μm diameter and the T matrix method for particles up to 12 μm. We investigate the impact of particle irregularity, composition, and size distribution on particle optical properties, and we develop optical models for representative natural mineral dust composition-size-shape types. Sensitivity studies with these models indicate that Multiangle Imaging Spectroradiometer (MISR) data should be able to distinguish plate-like from grain-like dust particles, weakly from strongly absorbing compositional types, and monomodal from bimodal size distributions. Models containing grain-like, weakly absorbing, bimodal distributions of dust particles were favored for optically thick Saharan and Asian dust plume examples, whereas strongly absorbing and plate-like particles were rejected. We will present detailed, systematic MISR sensitivity studies and analysis of more complex field cases using the optical models derived here in a future paper.