激光稳频技术在大气探测激光雷达中的应用研究进展

大气探测激光雷达因其时空分辨率高、探测精度高等特点,在大气探测、环境监测、国防安全等研究领域应用广泛。根据大气探测激光雷达的测量原理,其光源的频率稳定性会对大气参数的测量和反演产生巨大影响,因此,对光源进行稳频尤为重要。综述了目前应用于大气探测激光雷达的4种激光稳频技术及特点,介绍了这些稳频技术在大气探测激光雷达中的应用研究现状,为未来研制高精度大气探测激光雷达提供参考和借鉴。     

探测低空大气温度分布的转动拉曼激光雷达

提出了一种新的探测对流层低层大气温度的转动拉曼激光雷达方法,通过测量N2和O2的后向散射的纯转动拉曼谱的强度,计算它们的比值来确定大气温度的垂直分布,并对其性能进行了数值模拟。转动拉曼激光雷达的光源是一个调Q的Nd:YAG激光器,经扩束器后输出能量200mJ;采用双光栅单色仪提取所需要的氮气和氧气的转动拉曼谱;接收机采用光电倍增管和双通道光子计数器,量子效率是10%(48000个脉冲累加)。夜晚它对近地面10.2km高度内的探测信噪比在10:1以上,白天它对近地面3.6km高度内的探测信噪比在10:1以上,计算的温度与模拟用的温度真值阔线相差约0.3K。     

大气温室气体探测激光雷达及其标定技术研究进展

大气温室气体探测激光雷达是温室气体远程探测的重要手段,其探测技术和标定方法成为了各国温室气体探测的研究重点。综述了大气温室气体探测激光雷达技术及其标定方法的发展及应用,并对未来大气探测激光雷达的发展方向进行了展望。     

偏振微脉冲激光雷达对一次沙尘过程的探测分析

为研究沙尘暴的垂直分布及变化过程,在介绍偏振微脉冲激光雷达原理的基础上展示了自主研发的雷达系统。利用该系统监测了一次沙尘暴过程,通过分析这次沙尘过程的变化特点,认为此次过程包含有地面扬沙和高空输送两部分。数据分析表明,偏振微脉冲激光雷达具有较强的沙尘探测能力,可以直接反映沙尘垂直结构的分布状况和演变特征。     

宏/子脉冲编码光子计数激光雷达

光子计数激光雷达因其极高的探测灵敏度在远距离目标探测领域有着非常重要的作用。针对远距离、高速度的目标,普通的光子计数激光雷达无法简单通过统计直方图获得有用的回波信息。为了解决这一问题,本文提出了一种基于宏/子脉冲编码的光子计数激光雷达,利用时移脉冲累加的方法提取子脉冲的飞行时间进而在一个宏脉冲内获得目标距离信息。建立了宏/子脉冲编码光子计数激光雷达的理论模型,对虚警概率和探测概率的影响进行了分析,并通过蒙特卡洛仿真和实验验证了其对远距离高速径向运动目标探测的有效性。

     

GA-BP模型在大气微站数据修正中的应用

针对大气微站中的电化学气体传感器选择性不足,容易受到非目标气体交叉干扰的问题,提出使用遗传算法(GA)优化的反向传播(BP)神经网络模型(GA-BP模型)对微站进行数据修正的方法。GA-BP模型在善于处理非线性黑箱问题的BP神经网络模型的基础上引入具有全局寻优能力的GA,通过GA对神经网络的初始参数进行优化,弥补了BP神经网络容易陷入局部极小值的缺陷,提升了模型整体的精度和稳定性。实验结果表明,经过GA-BP模型修正后的微站可以实现对混合气体中的NO₂、CO、O₃和SO₂的准确定量分析,4种气体浓度的计算值和实测值之间的拟合优度(R²)均超过了0.95,与一元、多元线性回归和传统的BP神经网络相比,修正效果优势明显。此外,GA-BP模型还具有良好的泛化能力,将未参与训练的微站数据带入其中,得到的4种气体浓度计算值和实测值之间的R²值也均在0.88以上,证明了本方法具有很好的适用性,可以为厂家提升设备性能以及使用者得到准确的空气污染物的浓度数据提供有益的参考。     

基于啁啾脉冲的反射层析激光雷达成像

反射层析激光雷达成像具有系统简单及对湍流不敏感的优势,但普通脉冲发射信号难以兼顾远距离和高精度探测的要求.基于上述情况,本文提出了一种基于啁啾脉冲信号的反射层析激光雷达成像处理方法.该方法首先对啁啾脉冲回波进行相干压缩处理,通过对处理后信号的包络提取得到目标在各方向的反射层析投影数据,最后利用卷积反投影算法实现高分辨力的图像重构.仿真结果表明,在同一投影角度,利用该方法得到的包络与目标反射率投影相一致;在投影角度范围大于60°时能够得到目标的轮廓信息,角度范围越大,成像越精确.研究结果验证了该方法的有效性.     

集成化多线列激光雷达模拟前端微组件设计

多线列激光雷达具有广泛的需求,而现在的激光雷达探测处理电路多采用分立元器件组成,且探测器与处理电路相分离,存在体积大、成本高、可靠性差等问题.针对上述问题,本文基于系统级封装技术,设计了一种集成化的16元激光雷达模拟前端微组件,对多元激光雷达微组件的研究具有重要的现实意义.该组件集成了16元线列雪崩光电二极管探测器、自...     

大气气溶胶中有机氮和无机氮的测试方法及应用

选用元素分析仪测定大气气溶胶样品中的总氮含量,并使用总有机碳分析仪和离子色谱仪分别获得水溶性总氮和水溶性无机氮组分的含量;在此基础之上,通过相差法获得气溶胶中的水溶性有机氮和非水溶性氮组分含量;对本方法的精确度和准确度进行评估,及使用此方法对西安市大气细颗粒物PM2.5中含氮组分的进一步分析。结果表明,本方法能够系统准确地测试大气气溶胶中的多种含氮组分含量,可操作性强。     

Influence of Atmospheric Transmission on the Accuracy of Lidar Measurements of the Mie Scattering Power by Aerosol Particles

Measurement Techniques - The current issue of improving the lidar measurements accuracy has been considered. For a monostatic aerosol lidar, the degree of influence of atmospheric transmission at...     

经典Mie散射的数值计算方法改进

介绍一种改进的Mie散射数值计算方法,对Mie散射系数中不同的参量选用合适的递推关系进行计算,数值计算结果表明该方法具有快速、稳定、不受颗粒粒径和折射率范围影响的优点.     

经典Mie散射的数值计算方法改进

在光散射颗粒测量技术中,Mie散射理论的计算非常重要。本文介绍一种改进的Mie散射数值计算方法,通过对Mie散射系数进行重新构造,找到参量来控制Mie计算的收敛和计算精度。对各有关参量选用合适、稳定的递推关系进行计算。数值计算结果表明该方法具有快速、稳定的优点,可以在极大的颗粒粒径和折射率范围内得到合理结果。     

Selective Coloration of Melanin Nanospheres through Resonant Mie Scattering

Black melanin inks are prepared to selectively exhibit colors under strong light, inspired by human hair. High absorbance of melanin suppresses multiple scattering, causing resonant Mie scattering predominant. Various colors can be developed as the resonant wavelength dictated by nanosphere diameter. Therefore, the melanin inks can be used to encrypt and selectively disclose multicolor patterns for anticounterfeiting applications.     

Structural Information of the Volume Hologram from Mie Scattering

Abstract

Using Mie scattering theory, the imaging process of the volume hologram is described. The eigenequation and its integral kernel are obtained. Expressions for the maximum information density and for structural information are derived. Computations of eigenfunctions and eigenvalues for a two-dimensional object are presented.     

基于米氏散射的钧瓷乳光模拟计算

分别用米氏散射和瑞利散射对钧瓷内小气泡和分相液滴的散射进行模拟计算,以对比两种计算方法的差异.通过对比计算,解析了钧瓷乳光产生的机理.计算结果表明,对于单个颗粒的散射,气泡的散射远远大于分相.气泡和分相的散射都是各向异性,并且波长越短,散射越强.但它们对短波选择的程度随粒子半径变化是不同的,小气泡是单调的,而分相液滴会有极值出现.     

Fluorophore-Decorated Mie Resonant Silicon Nanosphere for Scattering/Fluorescence Dual-Mode Imaging

Inorganic nanoparticles with multiple functions have been attracting attention as multimodal nanoprobes in bioimaging, biomolecule detection, and medical diagnosis and treatment. A drawback of conventional metallic nanoparticle-based nanoprobes is the Ohmic losses that lead to fluorescence quenching of attached molecules and local heating under light irradiation. Here, metal-free nanoprobes capable of scattering/fluorescence dual-mode imaging are developed. The nanoprobes are composed of a silicon nanosphere core having efficient Mie scattering in the visible to near infrared range and a fluorophore doped silica shell. The dark-field scattering and photoluminescence images/spectra for nanoprobes made from different size silicon nanospheres and different kinds of fluorophores are studied by single particle spectroscopy. The fluorescence spectra are strongly modified by the Mie modes of a silicon nanosphere core. By comparing scattering and fluorescence spectra and calculated Purcell factors, the fluorescence enhancement factor is quantitatively discussed. In vitro scattering/fluorescence imaging studies on human cancer cells demonstrate that the developed nanoparticles work as scattering/fluorescence dual-mode imaging nanoprobes.     

火灾烟雾颗粒的光学散射特性研究

从理论和实验两个方面研究了几种常见的燃烧烟雾在不同波长激光下的散射特性。从Mie散射理论出发，比较几种Mie散射算法的优缺点，采用一种改进的连分式算法对火灾烟雾颗粒的散射光强分布进行计算，得出不同粒径大小和波长下光强分布图。结合理论计算，设计一套实验装置，测量并计算在不同角度下3种烟雾颗粒和面粉气溶胶散射光的相对光强比，实验测量值与理论计算值吻合较好。研究结果表明不同种类烟雾散射光相对光强比互不相同，火灾烟雾与非烟雾气溶胶差距较大，从而表明散射光相对光强比是区分不同烟雾特定的物性参数，为火灾烟雾探测技术发     

Tiny Peaks vs Mega Backgrounds: A General Spectroscopic Method with Applications in Resonant Raman Scattering and Atmospheric Absorptions

A simple method using standard spectrometers with charge-coupled device (CCD) detectors is described to routinely measure background-corrected spectra in situations where the signal is composed of weak spectral features (such as Raman peaks or absorption lines) engulfed in a much stronger (by as much as ～10(5)) broad background. The principle of the method is to subtract the dominant fixed-structure noise and obtain a shot-noise limited spectrum. The final noise level can therefore be reduced as desired by sufficient integration time. The method requires multiple shifts of the diffraction gratings to extract the pixel-dependent noise structure, which is then used as a flat-field correction. An original peak-retrieval procedure is proposed, demonstrating accurate determination of peak lineshapes and linewidths and robustness on practical examples where conventional methods would not be applicable. Examples are discussed to illustrate the potential of the technique to perform routine resonant Raman measurements of fluorescent dyes with high quantum yield, using conventional Raman systems. The method can equally be applied to other situations where small features are masked by a broad overwhelming background. An explicit example is given with the measurement of weak absorption lines in atmospheric gases.