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湿度环境下的气溶胶粒子群具有形状不一、成分不同、密度不等、复折射率多样、吸湿性参数不唯一、长短轴比不固定等复杂的微物理特性，并且这些物理量会直接影响激光的传输和散射特性。基于湿度环境下气溶胶粒子存在的各种可能性，本文充分考虑了气溶胶粒子的形态(球形、扁椭球形、长椭球形、不规则形)、尺度谱、复折射率、密度、长短轴比及其分布模型、吸湿性参数等理化特性的多样性，构建了一种复杂外混合气溶胶粒子群的光散射模型。基于该光散射模型，数值分析典型激光波长(0.78
mm、0.905 mm、1.064 mm、1.55 mm、2.1 mm)入射下不同混合比例和相对湿度对消光系数、单次散射反照率、不对称因子、散射相矩阵、后向散射系数、激光雷达比、线性退偏比等光学特性的影响。结果表明：消光系数、相函数P11对混合比例和相对湿度均表现出较强的敏感性，且随着相对湿度的增加，消光系数和相函数P11的前向散射也随之增大；相比混合比例，单次散射反照率、不对称因子对相对湿度更加敏感；不同散射角处的线偏振、圆偏振特性对相对湿度和波长的敏感性差异显著；后向散射系数和激光雷达比成反比，且它们对混合比例和相对湿度均比较敏感，相对湿度对线性退偏比的影响较大，而混合比例的影响较弱。本文所提出的复杂气溶胶光散射模型进一步丰富了气溶胶光学特性的研究，为研究不同湿度环境下的大气物理、遥感探测、光通信等应用提供了理论支撑。 The microphysical quantities (particle shape, composition, size, density, complex refractive index, size distribution model, aspect ratio, hygroscopic parameter, etc.) of the ensemble of complex externally mixed aerosol particles in humid environments (sea fog, water mist, haze, etc.) vary greatly. These microphysical quantities directly affect the laser transmission and scattering properties. Due to the optical properties (extinction coefficient, absorption coefficient, backscattering coefficient, phase function, etc.) of the ensemble of complex externally mixed aerosol particles directly determine the propagation properties of laser signals in the atmosphere, as well as the intensity and shape of echo signals. Therefore, studying the optical properties of the ensemble of complex externally mixed aerosol particles in humid environments is of significant importance for engineering applications such as autonomous driving, mapping, remote sensing detection, and more.
Based on the various possibilities of aerosol particles existing in humid environments, the diversity of physicochemical properties of aerosol particles, including their shape (sphere, oblate spheroid, prolate spheroid, and irregular), size distribution, complex refractive index, density, aspect ratio and its distribution models, as well as hygroscopicity parameters, etc., was fully taken into consideration in this paper. Therefore, a scattering model of the ensemble of complex externally mixed aerosol particles was presented in Section 2. Based on the presented complex aerosol scattering model, the influence of different mixing ratios (MR), and relative humidity (RH) on the optical properties, such as extinction coefficient, single scattering albedo, scattering phase matrix, asymmetry factor, backscattering coefficient, lidar ratio, and linear depolarization ratio, were numerically analyzed at typical laser wavelengths incident (0.78mm, 0.905 mm, 1.064 mm, 1.55 mm, and 2.1 mm).
In order to verify and illustrate the rationality of the complex aerosol scattering model presented in this paper, it was compared with the scattering model of maritime pollution aerosol in OPAC in Section 3.1. The results show that the optical properties of these two different aerosol scattering models vary similarly with wavelength, although differences exist; overall, the differences are relatively small. Therefore, the influences of MR on the optical properties of the ensemble of complex internally mixed aerosol particles were analyzed in Section 3.2. The influences of RH on the optical properties of the ensemble of complex internally mixed aerosol particles were also analyzed in Section 3.3. The numerical results indicate that the extinction coefficient and phase function P11 exhibit strong sensitivity to both the MR and RH. As RH increases, the extinction coefficient, and the forward scattering of P11 also increase. Compared to MR, single scattering albedo and asymmetry factor are more sensitive to RH. Significant differences in the sensitivity of linear, and circular polarization properties to RH and wavelength are observed at different scattering angles. The backscattering coefficient is found to be inversely proportional to the lidar ratio, and both the backscattering coefficient and lidar ratio are sensitive to MR and RH. It is observed that RH has a more pronounced effect on the linear depolarization ratio, while the influence of MR is weaker. The complex scattering model presented in this paper further expands the study of aerosol optical properties and provides theoretical support for studying engineering applications involving lasers in different RHs environments. It is worth emphasizing that this paper only focuses on external mixing. Therefore, the optical properties of the ensemble of complex internally mixed aerosol particles under different RHs will be the focus of future research. -
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