Lidar Ratio–Depolarization Ratio Relations of Atmospheric Dust Aerosols: The Super-Spheroid Model and High Spectral Resolution Lidar Observations

The backscattering optical properties of an ensemble of randomly oriented dust particles at a wavelength of 355 nm were comprehensively studied by examining the invariant imbedding T-matrix results of the super-spheroid dust model. In particular, we focused on the lidar ratio ((Formula presented.)) and depolarization ratio ((Formula presented.)) relations of dust aerosols to aid interpretation of data from the Atmospheric Lidar (ATLID) instrument that will be onboard the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) satellite. Super-spheroid models with various aspect ratios ((Formula presented.)), roundness parameters (Formula presented.), and refractive indices were investigated over a wide range of particle sizes and compared to the observation data of the National Aeronautics and Space Administration (NASA) Langley 355-nm airborne high spectral resolution lidar. We found that super-spheroid dust particles with different sets of (Formula presented.) and (Formula presented.) could be used to model almost the entire range of the observed joint distributions of (Formula presented.) and (Formula presented.). The (Formula presented.) relation could effectively discriminate among dust particle types. The observed (Formula presented.) and (Formula presented.) values with the largest population density were best covered by models with n > 2, especially by those with (Formula presented.) varying from 2.4 to 3.0.