Kahnert, M. and Kanngießer, Franz (2024) Optical Characterization of Marine Aerosols Using a Morphologically Realistic Model With Varying Water Content: Implications for Lidar Applications and Passive Polarimetric Remote Sensing. Geophysical Research Letters, 51 (5). Art.Nr. e2023GL107541. DOI 10.1029/2023GL107541.

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Abstract

Retrieving the physical properties and water content of marine aerosols requires understanding the links between the particles' optical and microphysical properties. By using a morphologically realistic model with varying salt mass fractions fm, describing the transition from irregularly shaped, dry salt crystals to brine-coated geometries, optical properties relevant to polarimetric remote sensing are computed at wavelengths of 532 and 1,064 nm. The extinction cross section and its color ratio depend on particle size, but are insensitive to changes in fm; thus, measured extinction coefficients at two wavelengths contain information on both particle number and size. The lidar ratio's dependence on both size and wavelength has implications for inverting the lidar equation. The results suggest that active observations of the backscattering cross section's color ratio and the depolarization ratio, as well as, passive observations of the degree of linear polarization offer avenues to obtain the water content of marine aerosols.

Key Points:
- Modeled extinction coefficient of marine aerosol depends on particle radius and wavelength, but not on water content
- The depolarization ratio and the color ratio of the backscattering cross section generally decrease with growing aerosol water content
- The linear polarization peak near backscattering angles at NIR wavelength could be used in passive polarimetry to retrieve water content

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