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

Abstract

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 (S $S$) and depolarization ratio (δ $\delta $) 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 (α $\alpha $), roundness parameters (n) $(n)$, 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 n $n$ and α $\alpha $ could be used to model almost the entire range of the observed joint distributions of S $S$ and δ $\delta $. The S−δ $S-\delta $ relation could effectively discriminate among dust particle types. The observed S $S$ and δ $\delta $ values with the largest population density were best covered by models with n > 2, especially by those with n $n$ varying from 2.4 to 3.0.

Sensitivities of Spectral Optical Properties of Dust Aerosols to Their Mineralogical and Microphysical Properties

“…Simulation results at 355 nm by Kong et al. (2022) show that the depolarization ratio is proportional to the dust particle effective radius when the effective radius is smaller than 0.3 μm. This corresponds with the results presented in Figure 15e.…”

“…In situ measurements (e.g., Freudenthaler et al, 2009;Haarig et al, 2017) give smaller values of the depolarization ratio, but show a similar spectrally consistent trend. Simulation results at 355 nm by Kong et al (2022) show that the depolarization ratio is proportional to the dust particle effective radius when the effective radius is smaller than 0.3 μm. This corresponds with the results presented in Figure 15e.…”

Single‐Scattering Properties of Encapsulated Fractal Black Carbon Particles Computed Using the Invariant Imbedding T‐Matrix Method and Deep Learning Approaches

“…One such property is the LDR, δ, which holds significant importance in lidar remote sensing. LDR can help identify the mixing state of aerosols and clouds (Burton et al., 2014; Kong et al., 2022). Another commonly measured property is the absorption enhancement E abs , which is used to evaluate absorption amplification, known as the “lensing effect” (Y. Zhang et al., 2018).…”

Understanding size-resolved dust emission from field measurements in Morocco

“…Furthermore, dust optical properties inferred assuming tri-axial ellipsoids agree with observations substantially better than when approximating dust by spheres or spheroids (Huang et al, 2020). This indicates that constraining dust shape is crucial to determine its optical and aerodynamic properties (Bi et al, 2009;Saito and Yang, 2021;Kong et al, 2022) and therefore make accurate estimations of dust impacts in the Earth System.…”