Linear depolarization of lidar returns by aged smoke particles

Area of Science:

• Atmospheric Science
• Optical Physics
• Remote Sensing

Background:

• Aged smoke plumes are significant atmospheric aerosols.
• Understanding smoke particle properties is crucial for climate and air quality models.
• Lidar measurements provide valuable data on aerosol optical properties.

Purpose of the Study:

• To analyze the spectral dependence of backscattering linear depolarization ratio (LDR) for aged smoke.
• To model the observed LDR spectral features using the T-matrix method.
• To determine the particle morphology and composition indicated by LDR measurements.

Main Methods:

• Numerically exact T-matrix method for light scattering calculations.
• Analysis of lidar backscattering linear depolarization ratio (LDR) measurements.
• Modeling spectral LDR dependence across multiple lidar wavelengths (355–1064 nm).

Main Results:

• The unique spectral dependence of LDR for aged smoke was successfully modeled.
• Modeling required assuming nonspherical smoke particle morphologies.
• Particles were inferred to contain significant amounts of nonabsorbing or weakly absorbing refractory materials, such as sulfates.

Conclusions:

• Spectral backscattering LDR measurements are indicative of morphologically complex smoke particles.
• Definitive characterization of smoke particle morphology and composition may require complementary measurements.
• Additional data from passive polarimetric or bistatic lidar could enhance particle analysis.