石墨气溶胶粒度分布及远红外消光因子研究

在烟幕试验箱中测试了不同湿度条件下超细石墨气溶胶的粒子分布及其随时间变化的规律。根据Mie散射理论计算了石墨气溶胶粒子对8～14μm远红外的消光因子。分析表明,石墨气溶胶的粒度随着分散时间延长和空气相对湿度减小而变小。小尺度的石墨气溶胶粒子对8～14μm红外的消光效率因子非常小,但随着气溶胶粒子直径的增加,消光效率因子显著变大并趋于稳定。直径大于2.5μm的石墨气溶胶粒子均能够对8～14μm远红外产生良好的消光效果。     

人造水雾粒度测试及红外消光因子计算分析

在大型半密闭空间内发生具有不同粒度分布的水雾体系,用喷雾激光粒度仪测试粒度分布规律并采用Van Der Hulst公式计算不同大小水雾粒子对红外辐射的散射效率因子、吸收效率因子和消光效率因子。结果表明:试验条件下水雾粒子的平均直径在5~65μm范围内。计算结果显示:水雾粒子对3～5、8～14μm红外辐射的消光作用主要取决于散射效应而非吸收效应。当水雾粒子的直径大于等于红外辐射的波长时,水雾体系对该波长红外辐射能够产生较强的消光效果。综合分析水雾体系的稳定性和消光特性,直径在3~30μm之间的水雾粒子对3～5、8～14μm红外辐射的衰减效果更为明显。     

水溶性气溶胶对自由空间量子通信性能影响

为了研究水溶性气溶胶对量子通信的影响,本文根据水溶性有机碳(WSOC)的复折射率及Mie散射理论得到其消光效率因子,分析了水溶性气溶胶粒子质量浓度对量子通信链路衰减、信道容量、信道生存函数以及信道误码率的影响并进行了仿真实验。结果表明,当传输距离为8 km,水溶性气溶胶粒子质量浓度分别为1.5μg/m³和6.5μg/m³时,对应的链路衰减、信道容量和信道误码率分别为0.506 d B/km和2.193 dB/km、0.622 bit/s和0.314 bit/s、0.0055和0.0099;当水溶性气溶胶粒子浓度为4μg/m³,传输距离分别为4 km和10 km时,对应的信道容量保真度分别为0.82和0.45。实际进行量子通信时,应根据水溶性气溶胶粒子的浓度来调整各项性能参数以保证通信正常进行。     

气溶胶对电磁信号的影响分析

气溶胶作为大气电磁环境的重要组成部分,对电磁信号具有很强的吸收和散射作用,从而影响电磁信号的传输质量,本文分析了气溶胶和电磁信号的相互作用机理,利用Mie散射给出了球形气溶胶粒子的散射、吸收和消光效率因子以及不对称因子随电磁信号波长变化的数值结果,为提高电磁信号传输质量提供了理论参考。     

红磷烟幕粒度测试及红外消光因子计算分析

测试了红磷烟幕的粒度分布及平均直径,给出了典型样品的累积曲线.根据Mie散射理论计算了多种直径红磷烟幕粒子对不同波长红外的吸收效率因子、散射效率因子和消光效率因子.分析表明,红磷烟幕粒子的直径与成烟时间和环境湿度有很大关系,其面积平均直径分布在0.5～30μm范围内;小尺度红磷烟幕粒子对红外的吸收效应比较明显,随着粒子直径增大,散射效应和吸收效应逐渐接近一致.最大消光效率因子对应的波长随着入射波长的增大而逐渐增加.     

雾对“日盲”紫外光传输的影响分析

该文从"日盲"紫外光的传输特性出发,利用经典散射理论以及前向散射修正,再结合雾粒子尺度分布,对紫外光在雾中传输的衰减公式进行推导,应用新的公式,对紫外光传输的衰减进行计算机仿真,得出相关结论。     

旋芯直径对喷嘴雾化特性的影响

针对现有旋芯需要高压雾化的问题,设计一种低压下能达到同等雾化性能的旋芯喷嘴,利用激光多普勒粒子分析仪测试不同旋芯直径和流道直径时距离喷嘴1 m处雾滴的中位直径、速度和雾锥角。结果表明:当水压为0.9~1.2 MPa时,喷嘴所形成的雾滴的中位直径均小于100μm,说明了旋芯喷嘴改进的合理性;旋芯直径越大,雾滴的中位直径和速度越小,雾锥角越大。     

气溶胶粒子特性对激光衰减系数的影响

1.06 μm激光通常依赖经验数据或典型气溶胶模式计算大气消光系数,无法将理论计算与实际的气溶胶情况相结合,其精度无法满足激光武器的要求.本文通过在绥中地区多种天气下进行的1.06 μm激光大气衰减实验,验证了依据气溶胶大气模型数据计算得到的消光系数与真实数据存在较大误差,即典型气溶胶模式与绥中地区实际气溶胶情况不一致...     

一种半导体激光云高仪时序控制和信号处理方案

半导体激光云高仪APD探测器获取的大气气溶胶后向散射信号信噪比较低,难以直接用于反演云高、垂直能见度等大气参数.针对后向散射信号的这种特点,提出了一种半导体激光云高仪时序控制和信号处理实现方案,在完成后向散射信号的高速采集、分段累积平均的同时实现整个系统发射、接收、维护、数据存储和上传等复杂时序控制.经对比实验验证,该...     

卫星遥感气溶胶光学厚度的双通道方法

本文提出了一种利用ＮＯＡＡ－１４极轨卫星甚高分辨率辐射计可见光和近红外两个通道的反射率资料遥感晴空条件下，均匀下垫面上整层大气气溶胶光学厚度的双通道方法。该方法利用气溶胶散射的波长关系，把基于大气辐射传输方程近红外通道的光学厚度均值引入可见通道，使单个通道中地表反射率和大气因子参数化的误差得以抵消，极大地提高遥感精度。     

Propagation at 10 microm through smoke produced by atmospheric combustion of diesel fuel

Absorption and extinction due to the smoke produced by the atmospheric combustion of diesel fuel have been measured using a CO2 laser spectrophone at a wavelength of 10.6 microm. The absorption coefficient normalized to the aerosol mass density is 0.84 +/-0.076 m2/g, and the total scattering coefficient (the difference between the extinction and absorption values) normalized in the same way is 0.15 +/- 0.014 m2/g. The largely fibrous aerosol was found to be 80% carbon, with most of the remainder consisting of hydrocarbons which are comparatively transparent at 10.6 microm and physically resemble the unburned fuel. The normalized coefficients of this study approximate those of diesel automobile effluents. This is not surprising since the aerosol composition and morphology appear to be similar.     

Empirical relationships between extinction coefficient and visibility in fog

Relationships between visibility and an extinction coefficient that is due to fog in optical windows that are free from molecular absorption are derived. The extinction coefficients in the visible (0.55 microm), the near IR (1.2 microm), and the mid IR (3.7 microm) are comparable to and roughly twice as much as that in the far IR (10.6 microm) when visibility is less than a few hundred meters. The advantage of far-IR radiation compared with shorter wavelengths grows as visibility exceeds 500 m. Correspondingly, the relationship between extinction coefficient and visibility becomes more sensitive to variations in the particle-size distribution of fog.     

Differences arising in the determination of the atmospheric extinction coefficient by transmission and target reflectance measurements

Measurements of the optical extinction at a wavelength of 1.06 microm have been made in water droplet clouds. The extinction coefficient has been measured in the laboratory using two different methods simultaneously. In the first, measurements of the transmitted signal attenuation over a known path length were used. In the second the extinction coefficient was derived from the two-way attenuation of the signal reflected from a target on the opposite side of the cloud from the laser source and detector. It is found that in general the two values of the coefficient derived differ considerably, and the magnitude of the difference depends on the cloud density, the target size, and the system's optical parameters. The difference is shown to originate in the off-axis forward scattering caused by the cloud droplets, and the implications of the results on the measurement of the atmospheric extinction by reflection (lidar) techniques are discussed.     

Optical Properties of Polydispersed Atmospheric Aerosols Following Wet Removal

It is well known that size distributions of aerosols influence their optical properties. Many previous studies have focused on the optical properties of aerosols with particular weather conditions, such as haze, fog, or pollution. However, few studies have investigated the influence of precipitation on the optical properties of aerosols. In this study, the optical properties of polydispersed atmospheric aerosols following a wet removal process were investigated. For these calculations, a lognormal distribution was used to represent the raindrop size distribution and the tri-modal aerosol size distributions. Variations in aerosol size distributions and the corresponding changes an extinction coefficient caused by the wet scavenging process were quantified with different compositions of aerosols as a function of rain intensity. The results showed that the extinction coefficient decreased and the corresponding visibility was enhanced with the precipitation duration because of the precipitation scavenging. It was also shown that the rain intensity and the refractive index and size distribution of aerosols influenced the calculations of extinction coefficient of aerosols.     

Aerosol extinction models based on measurements at two sites in Sweden

Two aerosol extinction models have been developed using statistical analysis of long-term optical transmission measurements in Sweden performed at two locations from July 1977 to June 1982. The aerosol volume extinction coefficient for infrared (IR) radiation is calculated by the models with visibility, temperature, and air pressure as input parameters. As in the MODTRAN model, the IR extinction coefficient is proportional to the coefficient at 550 nm, which depends on the visibility. In the new models, the wavelength dependence of the extinction also depends on the visibility. The models predict significantly higher attenuation in the IR than does the Rural aerosol model from MODTRAN, which is commonly used. Comparison with the Maritime model shows that the new models predict lower extinction values in the 3-5 microm region and higher values in the 8-12 microm region. The uncertainties in terms of variance levels are calculated by the models. The properties of aerosols, and thereby the extinction coefficient, are partly correlated to local meteorological parameters, which enables the calculation of a mean predicted value. A substantial part of the variation is, however, caused by conditions in the source area and along the trajectory path of the aerosols. They are not correlated to the local meteorological parameters and therefore cause the variance in the models.     

Visible and infrared extinction of atmospheric aerosol in the marine and coastal environment

The microphysical model Marine Aerosol Extinction Profiles (MaexPro) for surface layer marine and coastal atmospheric aerosols, which is based on long-term observations of size distributions for 0.01-100 μm particles, is presented. The fundamental feature of the model is a parameterization of amplitudes and widths for aerosol modes of the aerosol size distribution function (ASDF) as functions of fetch and wind speed. The shape of the ASDF and its dependence on meteorological parameters, altitudes above the sea level (H), fetch (X), wind speed (U), and relative humidity is investigated. The model is primarily to characterize aerosols for the near-surface layer (within 25 m). The model is also applicable to higher altitudes within the atmospheric boundary layer, where the change in the vertical profile of aerosol is not very large. In this case, it is only valid for "clean" marine environments, in the absence of air pollution or any other major sources of continental aerosols, such desert dust or smoke from biomass burning. The spectral profiles of the aerosol extinction coefficients calculated by MaexPro are in good agreement with observational data and the numerical results obtained by the well-known Navy Aerosol Model and Advanced Navy Aerosol Model codes. Moreover, MaexPro was found to be an accurate and reliable instrument for investigation of the optical properties of atmospheric aerosols.     

Measured Infrared Spectral Extinction for Aerosolized Bacillus subtilis var. niger Endospores from 3 to 13 mum

We measured spectral extinction in situ for aerosolized Bacillus subtilis var. niger endospores using Fourier-transform infrared spectroscopy from 3.0 to 13.0 mum. Corresponding aerosol size distributions were measured with a commercially available elastic light-scattering probe and verified by direct particle capture and subsequent counting by video microscopy. Aerosol mass density was monitored simultaneously with conventional dosimetry and was used to mass normalize the measured spectral extinction. Mie theory calculations based on measured distributions and available complex indices of refraction agreed well. We also present resultant Mie calculations for the absorption, total scattering, and backscatter. For comparison, measured spectral extinction for three common environmental aerosols is also presented, i.e., for water fog, diesel soot, and Arizona road dust.     

激光通信中雨滴、烟雾信道相干带宽特性研究

本文选用合理的模型模拟了大气信道中雨滴、烟雾带来的相干带宽,并进行了数值计算。结果表明:对于雨滴、轻雾信道,相干带宽很宽;而对于烟雾浓度较大的信道,信道的相干带宽应引起激光大气通信的重视。