Improvement of aerosol fine mode fraction retrieval from skylight measurements by degree of linear polarization: information content analysis

Fengxun Zheng; Weizhen Hou; Zhengqiang Li

doi:10.1117/12.2572302

5 November 2020 Improvement of aerosol fine mode fraction retrieval from skylight measurements by degree of linear polarization: information content analysis

Fengxun Zheng, Weizhen Hou, Zhengqiang Li

Author Affiliations +

Proceedings Volume 11566, AOPC 2020: Optical Spectroscopy and Imaging; and Biomedical Optics; 1156602 (2020) https://doi.org/10.1117/12.2572302
Event: Applied Optics and Photonics China (AOPC 2020), 2020, Beijing, China

Abstract

Aerosol fine mode fraction (FMF) is an important parameter in associating aerosol loading with fine particle matter (PM2.5) pollution in the atmosphere. Previous studies have retrieved FMF from scalar measurements (centered at 490, 550, 670, 870, 1610 nm) from Synchronization Monitoring Atmospheric Corrector (SMAC) sensor. As a polarimetric instrument, SMAC also provides degree of linear polarization (DOLP) measurements (centered at 490, 670, 870, 1610 nm). In this paper, we try to evaluate the capabilities of both scalar and polarimetric measurements for aerosol retrieval. For the purpose, the analyses of information content and errors propagation are performed based on synthesized SMAC data. The Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is adopted as the forward model, and the ground-based skylight measurements on the solar principal plane are simulated. Additionally, the analytic formula used to calculate Jacobians of DOLP with regard to FMF is verified by the finite difference method. Secondly, based on the information content analysis theory, the degree of freedom for signal (DFS) of FMF contained in polarimetric observations are calculated. Meanwhile, the a posteriori error of FMF are also calculated for the error propagation analysis. We found the mean DFS of FMF is greater than 0.8, which indicates that the FMF can be well retrieved from both intensity and polarization measurements. Compared to scalar measurements, the DOLP measurements can provide extra 0.14 and 0.08 DFS for fine- and coarse-dominated aerosols, respectively. As for the inversion errors, the uncertainties of both AOD and FMF decrease apparently. The a posteriori error of AOD decreases from 23.33% to 11.6%, and the a posteriori error of FMF decreases from 33.8% to 26.5%.

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Fengxun Zheng, Weizhen Hou, and Zhengqiang Li "Improvement of aerosol fine mode fraction retrieval from skylight measurements by degree of linear polarization: information content analysis", Proc. SPIE 11566, AOPC 2020: Optical Spectroscopy and Imaging; and Biomedical Optics, 1156602 (5 November 2020); https://doi.org/10.1117/12.2572302

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KEYWORDS

Aerosols

Scattering

Polarization

Atmospheric modeling

Polarimetry

Atmospheric particles

Error analysis

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