Abstract
The comparison of the angular light-scattering method (ALSM) and the spectral extinction method (SEM) in solving the inverse problem of aerosol size distribution (ASD) are studied. The inverse problem is solved by a SPSO-DE hybrid algorithm, which is based on the stochastic particle swarm optimization (SPSO) algorithm and differential evolution (DE) algorithm. To improve the retrieval accuracy, the sensitivity analysis of measurement signals to characteristic parameters in ASDs is studied; and the corresponding optimal measurement angle selection region for ALSM and optimal measurement wavelength selection region for SEM are proposed, respectively. Results show that more satisfactory convergence properties can be obtained by using the SPSO-DE hybrid algorithm. Moreover, short measurement wavelengths and forward measurement angles are beneficial to obtaining more accurate results. Then, common monomodal and bimodal ASDs are estimated under different random measurement errors by using ALSM and SEM, respectively. Numerical tests show that retrieval results by using ALSM show better convergence accuracy and robustness than those by using SEM, which is attributed to the distribution of the objective function value. As a whole, considering the convergence properties and the independence on prior optical information, the ALSM combined with SPSO-DE hybrid algorithm provides a more effective and reliable technique to obtain the ASDs.
Highlights
Atmospheric aerosols are important drivers of air quality, atmospheric heat radiative balance, human health and climate, etc
There are several global ground-based aerosol observation networks and satellite instrument networks that have been established to study the properties of the atmospheric aerosols, e.g., AERONET, MODIS [5,6,7,8], determining the aerosol size distribution (ASD) accurately is still regarded as an unsolved problem and needs further research
Unlike the spectral extinction method (SEM), only single spectral information of aerosol is required by using angular light-scattering method (ALSM), and the ASDs can be recovered by measuring multi-angle light-scattering signals [12,13]
Summary
Atmospheric aerosols are important drivers of air quality, atmospheric heat radiative balance, human health and climate, etc. All the satisfactory results obtained by using SEM were based on having sufficient spectral measurement information about the aerosol dispersion system beforehand, e.g., the multi-spectral transmittance signals. To obtain these information measurements, the multi-spectral light source and detector should be needed, and the multi-spectral optical constants of aerosol should be known, which may increase the difficulty and the cost of experiment. Unlike the SEM, only single spectral information of aerosol is required by using ALSM, and the ASDs can be recovered by measuring multi-angle light-scattering signals [12,13]. Common monomodal and bimodal ASDs are retrieved by SEM and ALSM, respectively, and the main conclusions and perspectives are provided
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