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Abstract. The lidar backscattering properties of Asian dust particles, namely the lidar ratio (S) and backscattering depolarization ratio (δ), were studied using a discrete dipole approximation (DDA) model. The three-dimensional morphology of the dust particles was reconstructed in fine detail using the focused ion beam (FIB) tomography technique. An index based on the symmetry of the scattering matrix was developed to assess the convergence of random orientation computation using DDA. Both S and δ exhibit an asymptotic trend with dust particle size: the S initially decreases, while the δ increases with size, before both approach their asymptotic values. The lidar properties were found to have statistically insignificant dependence on effective sphericity. The presence of strongly absorbing minerals, such as magnetite, can greatly reduce the dust's single-scattering albedo and δ. Utilizing the robust asymptotic trend behavior, two parameterization schemes were developed: one to estimate the δ of a single dust particle given its size and the other to estimate the δ of dust particles with a lognormal particle size distribution given the effective radius. The parameterization scheme was compared with results based on the TAMUdust2020 database, showing hexahedrons to reasonably represent realistic geometries with similar physical properties.
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Polarized lidar and ocean particles: Insights from a mesoscale coccolithophore bloom
Oceanographic lidar can provide remote estimates of the vertical distribution of suspended particles in natural waters, potentially revolutionizing our ability to characterize the distribution of marine ecosystems and properly represent them in models of upper ocean biogeochemistry. However, lidar signals exhibit complex dependencies on water column inherent optical properties (IOPs) and instrument characteristics, which complicate efforts to derive meaningful biogeochemical properties from lidar return signals. In this study, we used a ship-based system to measure the lidar attenuation coefficient () and linear depolarization () across a variety of optically and biogeochemically distinct water masses, including turbid coastal waters, clear oligotrophic waters, and calcite rich waters associated with a mesoscale coccolithophore bloom. Sea surface IOPs were measured continuously while underway to characterize the response of and to changes in particle abundance and composition. The magnitude of was consistent with the diffuse attenuation coefficient (Kd), though the -Kd relationship was nonlinear. was positively related to the scattering optical depth and the calcite fraction of backscattering. A statistical fit to these data (r2 = 0.69) suggests that polarized forward scattering properties of calcified particles are distinct, and contribute to measurable differences in the lidar depolarization ratio. A better understanding of the polarized scattering properties of coccolithophores and other marine particles will further our ability to interpret polarized oceanographic lidar measurements, and may lead to new techniques for measuring the material properties of marine particles remotely.
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- Award ID(s):
- 1635748
- PAR ID:
- 10302640
- Date Published:
- Journal Name:
- Applied optics
- Volume:
- 59
- Issue:
- 15
- ISSN:
- 0066-5495
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/AO.389845
