In the marine environment, sea salt aerosol particles transition from cubic or rectangular shapes when dry to various non-spherical shapes like ellipsoids and cylinders under different humidities. The complex humidity conditions and particle morphologies pose challenges to simulating the optical scattering properties of non-spherical sea salt aerosols. This study, addressing real environmental scenarios, employs the randomly oriented T-matrix computational method to calculate the optical scattering and polarization characteristics of sea salt aerosols at a wavelength of 1.06 μm under three relative humidity conditions (50%, 80%, and 95%) and three particle morphologies (spheroid, circular cylinder, and Chebyshev particle shapes). The results show the following: (1) In terms of optical scattering properties, the greater the non-sphericity of particles under the same humidity conditions, the larger the deviation between non-spherical and spherical models. For spheroid and circular cylinder sea salt aerosols, the error in the extinction efficiency factor mainly lies within 10–30%, reaching up to 120%; the error in the asymmetry factor is primarily between 3 and 25%, with a maximum of 75%, and the error in the forward-scattering phase function is mainly within 10–60%, reaching up to 180%. Chebyshev particle-shaped sea salt aerosols exhibit smaller deviations in optical scattering properties compared to equivalent spherical models, generally within the 5–25% range. Under different humidity conditions, the scattering characteristic parameters of sea salt aerosol particles for various non-spherical models show a positive correlation with relative humidity. When relative humidity is below 70%, the optical scattering properties of differently shaped sea salt aerosols are less affected by relative humidity. Above 70% relative humidity, the optical scattering properties of sea salt aerosols of different shapes become more sensitive to changes in relative humidity. (2) Regarding polarization properties, the greater the humidity, the more significant the impact on polarization properties, and as humidity increases, sea salt aerosols with higher non-sphericity exhibit more complex changes in polarization characteristics. The differences in shapes of non-spherical models mainly affect the numerical values of polarization properties. Under the same humidity conditions, spheroid polarization characteristics are significantly different from other models. In terms of depolarization ratio for aerosols, circular cylinder sea salt aerosols show the highest depolarization ratio at various relative humidities, followed by spheroid, with Chebyshev-shaped having the least. The effect of relative humidity on the depolarization ratio varies with the scattering angle. The higher the relative humidity, the more complex the variation in the depolarization ratio with scattering angle, with more pronounced oscillations in the curve, and the less non-spherical the shape, the more intense the oscillations in the depolarization ratio curve due to humidity. In conclusion, this study calculated the optical scattering and polarization properties of sea salt aerosol particles under different relative humidities and shapes, which is of significant importance for applications like 1.06 μm laser engineering and atmospheric radiation transmission in actual marine scenarios.

The T-matrix method was utilized to study the polarization characteristics of nonspherical sea salt aerosol models within the wavelength range of 0.48–2.5 µm. Analysis was conducted on the polarization characteristics of nonspherical sea salt aerosols across different wavelengths as a function of scattering angle. This included scrutinizing linear depolarization ratios under typical visible and near-infrared wavelengths for various aspect ratios. The impact of particle nonsphericity on the linear depolarization ratios of monodisperse and polydisperse sea salt aerosol particles was examined. The results indicate: (1) In the analysis of the polarization characteristics of sea salt aerosols, the trends of polarization properties are similar between monodisperse and polydisperse systems. The scattering phase function P₁₁(θ) is predominantly more significant in the forward-scattering direction. P11(θ) is insensitive to wavelength changes in the backward-scattering direction. P₃₃(θ)/P₁₁(θ) varies across different bands; in the visible light spectrum, there are significant fluctuating changes, while in the infrared spectrum, it trends towards nearly linear changes. The variation trends of −P₁₂(θ)/P₁₁(θ) and P₃₄(θ)/P₁₁(θ) with scattering angle are similar, and both are significantly affected by changes in wavelength. (2) Regarding the depolarization ratio of sea salt aerosols, the value for polydisperse systems is more than twice that of monodisperse systems, and the greater the nonsphericity, the higher the linear depolarization ratio. In monodisperse systems, at a wavelength of 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 118.82, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum depolarization ratio is near 97.52; under polydisperse conditions, at 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 117.18, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum linear depolarization ratio is near 215.66. Investigating the polarization characteristics and linear depolarization ratios of nonspherical spheroid sea salt aerosol particle models at all scattering angles is important for remote-sensing detection, high-precision calibration, and other optoelectronic applications.

Aerosols significantly affect the transmission of optical signals in the atmosphere, necessitating accurate atmospheric models for the performance evaluation of electro-optic devices. Aerosol size distribution is a critical parameter in these models, and the lognormal function is commonly used to mathematically represent it. This study aims to handle the lack of a solid criterion for determining the number of lognormal modes and introduces an improved scheme that leverages the characteristics of the second derivative (SD) of the Gaussian curve to identify the mode amount and to initialize mode parameters for fitting. The optimization problem is solved using a genetic algorithm, incorporating a goodness-of-fit index to determine the presence of spurious modes. For aerosol size distributions characterized by a single Gaussian peak, mode parameters such as mode radius and width can be straightforwardly identified through the positions of peaks and roots on the SD curve. However, the original mode dissociation method may overlook potential modes in distributions composed of superimposed Gaussian peaks. Numerical tests indicate that such oversights can result in substantial errors in calculating the aerosol extinction coefficient, with relative errors exceeding 100%. The proposed scheme significantly enhances the accuracy of mode dissociation in aerosol size distribution, reducing errors in aerosol extinction coefficient calculations by approximately 40% when applied to data from the Aerosol Robotic Network (AERONET). An additional benefit of this method is its ability to constrain the number of lognormal modes in an aerosol size distribution. Results from applying this scheme to data from selected AERONET sites reveal that over half of the size distributions consist of more than two lognormal modes, highlighting the effectiveness of the proposed approach in capturing complex aerosol behaviors.

The variation in key parameters of the solar–terrestrial space during two consecutive auroral disturbances (the magnetic storm index, Dst index = −422 nT) that occurred during the 18–23 November 2003 period was analyzed in this paper, as well as the spatiotemporal characteristics of NO 5.3 μm radiation with an altitude around the location of 55°N 160°W. The altitude was divided into four regions (50–100 km, 100–150 km, 150–200 km, and 200–250 km), and it was found that the greatest amplification occurs at the altitude of 200–250 km. However, the radiance reached a maximum of 3.38 × 10⁻³ W/m²/sr at the altitude of 123 km during the aurora event, which was approximately 10 times higher than the usual value during “quiet periods”. Based on these findings, the spatiotemporal variations in NO 5.3 μm radiance within the range of latitude 51°S–83°N and longitude of 60°W–160°W were analyzed at 120 km, revealing an asymmetry between the northern and southern hemispheres during the recovery period. Additionally, the recovery was also influenced by the superposition of a second auroral event. The data used in this study were obtained from the OMNI database and the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) infrared radiometer onboard the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite. Finally, the correlation of NO 5.3 μm radiance at 120 km with temperature, solar wind speed, auroral electrojet index (AE index), and Dst index were analyzed. It was found that only the Dst index had a good correlation with the radiance value. Furthermore, the correlation between the Dst index and radiance at different altitudes was also analyzed, and the highest correlation was found at 170 km.

Sky background radiance serves as a crucial background element in optical imaging, target detection, and atmospheric remote sensing. This study assesses the capability of the CART radiative transfer model to replicate the characteristics of full - sky background radiance. It does so by comparing the model simulations with the measurements obtained from a spectral full - sky background radiometer in typical regions. The angular and spectral variations of sky radiance are examined under different viewing geometries. Additionally, comparisons between the model results and measurements are carried out for representative broadband and narrowband integrations. The calculated full - sky radiance distributions exhibit a good agreement with the overall angular patterns of the measured data. However, the most significant discrepancies are observed at small forward - scattering angles, as it is challenging to represent real aerosol phase functions using simplified aerosol models. For representative cloud - free directions, the maximum mean relative error of the reported comparison groups is less than 9.6%. This indicates that the CART model can provide reliable full - sky background radiance simulations for infrared target - background analysis and atmospheric transmission studies.