Theory of multiwave differential optical absorption spectroscopy surface ozone measurement with open path meters

The multiwave differential optical absorption spectroscopy (DOAS) technique is normally applied to obtain information on a few gas components in a mixture, as well as to reduce errors while evaluating their concentrations. Multiwave measurements also lead to a universal concept for analysing possible sources of errors affecting the accuracy of gas concentrations. This method allows precise estimation of the contribution of every error source to measurement results. A mathematical formulation of multiwave technique for measuring surface ozone concentration with a DOAS open path instrument is presented here along with an analysis of the role of spectral differences in the sounding radiation emitted to sondage and auxiliary routes.     

Atmospheric aerosol measurements and the reliability problem: new results

Atmospheric aerosol measurements and the reliability problem have been discussed previously. New results of the inverse problem solutions are discussed here. The relationship between the backscattering coefficient and the extinction coefficient was found for different approximations of the integral method using finite duration probe pulses. The optical thickness of the atmosphere was determined by methods of multiposition probing without numerical integration. The integral algorithms for the determination of the extinction coefficients can be more accurate than the algorithms for the determination of the optical thicknesses. New algorithms were developed for the determination of the relationship between the optical parameters of aerosols. New lidar equation solutions developed for weak signal processing were investigated. The errors of the extinction coefficient for different minimizing procedures were considered based on the weighting coefficients. A method was developed to determine the weighting coefficients. The preliminary calculated parameters were used for more accurate linearization of the inverse problem. The model of spherical particles with the radially variable refractive index was considered. The effectiveness of the proposed model is based on the possibility of choosing the thickness of inhomogeneous coating depending on the particle size. The proposed model can explain the significant discrepancy found between the photoelectric and filter aspiration results and can be used to minimize the error of particle size optical determination.     

气体静压导轨气膜厚度的电容式测试方法

气体静压导轨是超精密工程的核心基础技术之一,其气膜振动是影响加工精度的主要因素。提出了一种气体静压导轨气膜厚度的电容式测试方法,将气体静压导轨的节流器工作底面与实验台面当作电容式传感器的2个极板,当气膜厚度发生变化时,电容将产生较大变化。通过测量节流器与工作面间的电容,计算得到气膜厚度值。同时建立了不同凹面节流器电容与气膜厚度的数学模型。实验利用电容测量仪与电感测微测头同时对气膜厚度进行测量,结果显示两者误差为0.42μm,为气体静压导轨气膜厚度的测量提供了新的方法。     

Analysis of the atmospheric and emissivity influence on the splitwindow equation for sea surface temperature

In this paper we have analysed the effects of the different atmospheric species (water vapour, fixed gases and aerosols) and the surface emissivity on the split-window method for determining the sea surface temperature. The widely used split-window method is based on the differential absorption of water vapour in the atmospheric window 10.5ndash;12.5 μm. Other atmospheric species with absorption coefficients different to that of water vapour can then have a large influence on the split-window. The effect of gases, such as C0₂, N₂0, CH₄, CO and 0₃, and maritime aerosols is evaluated by comparing the effect of the water vapour alone. To do this we simulated AVHRR measurements in channels 4 and 5 for a set of mid-latitude atmospheres using LOWTRAN 7 code. Our results indicated that the fixed gases have a negative effect on the split-window specially for dry atmospheres; in this case the error in retrieved temperatures was shown to increase by about 70 per cent with respect to that obtained considering water vapour only. The effect of maritime aerosols was parameterised in terms of the surface meteorological range and the path optical thickness was measured at 0.55 μm, which can be obtained from both visible channels of AVHRR. The total effect on the split-window appeared to be a linear function of the path optical thickness. On the other hand, we analysed the impact of sea surface emissivity showing that it is strongly dependent on the observation angle, especially for angles larger than 40°. In addition to this it has been shown that the emissivity effect depends on the atmospheric moisture. However, for angles lower than 40° the atmospherically averaged emissivity effect is close to zero. Finally we have given a correction algorithm accounting for all the studied effects, yielding an error estimated at 0–34 degK. over the simulated mid-latitude data set.     

多声路超声波流量计在引水明渠中的流量测量分析

介绍了多声路超声波流量计在明渠中的流量测量原理,并通过多声路时差式超声波流量计在引水明渠上的实例应用对影响流量测量的误差源进行了具体的分析。     

Cross-sensitivity evaluation for ammonia sensing using absorption spectroscopy in the UV region

This paper describes an optical sensor for the monitoring of ammonia gas. An open path optical technique is used to analyze the absorption lines of ammonia within the ultra-violet region. The optical sensor shows absorption lines comparable to the theoretical ammonia spectra. Cross-sensitivity with carbon dioxide and oxygen gas has been tested and clearly shows that these two gases have no effect on ammonia measurement in the ultra-violet region, between 200 nm and 230 nm. The optical sensor is able to detect ammonia down to 9 ppm with an average error less than 2%. The optical sensor system also shows a fast response time which is less than 4 s.     

Fuzzy-genetic optimization of the parameters of a low cost system for the optical measurement of several dimensions of vehicles

When designing optical measurement systems, it is common to use cameras, lenses and frame grabbers specially designed for metrology applications. These devices are expensive, therefore optical metrology is not the technology of choice in low cost applications. On the contrary to this, surveillance video cameras and home oriented frame grabbers are cheap, but imprecise. Their use introduces inaccuracies in the measurements, that sometimes can be compensated by software. Following this last approach, in this paper it is proposed to use fuzzy techniques to exploit the tolerance for imprecision of a practical metrology application (to automate the measurement of vehicle dimensions in Technical Inspection of Vehicles in Spain, the equivalent of the Ministry Of Transport Test or MOT Test in UK) and to find an economic solution. It will be shown that a genetic algorithm (GA), guided by a fuzzy characterization of the sources of error, can optimize the placement of the video cameras in a station so that these mentioned sensors can be used to take measurements within the required tolerance. Supported by the Spanish Ministry of Science and Technology under Projects TIN-2005-08386-C05-05 and TIN-2005-08386-C05-01.     

测量甲烷体积分数的高灵敏度光纤传感器研究

基于气体的红外吸收原理,研究了一种能在复杂环境下测量甲烷气体体积分数的新方法.这种方法可以有效地减小由于光源的不稳定、环境的变化而引起的测量误差.在这种测量方法中设计了一条参考测量光路,此参考测量光路和测量光路同时随环境的变化而变化,通过对待测量气体光路与参考气体测量光路作对比而得出较为准确的待测甲烷气体体积分数.     

Design of optical path of pickup for small form factor optical disk drive

We designed an optical path of pickup for the small form factor optical disk drive that is compatible with Blu-ray Disc format using 405 nm wavelength laser, 0.85 NA objective lens, and the 0.1-mm thick cover layer. The optical path consists of a high NA objective lens, a micro compensatory lens that is fabricated by micro-molding process, three reflective mirrors and a partial mirror. The optical performance of the optical path is analyzed and the expected yield ratio is calculated for 22 tolerance parameters by using Monte Carlo method. Finally, the micro compensatory lens is fabricated by micro-molding process.     

火灾烟气中CO和烟颗粒的光声复合探测方法

利用气体滤波光声技术和光散射原理测量早期火灾烟气中CO和烟颗粒浓度的方法和系统.分别采用两个气体滤波光声腔的作为CO测量光声腔和烟雾参比光声腔,在光源和光声腔之间建立火灾烟气的测量路径,记录其进入该路径后光声信号强度的变化,通过两个滤波波长上CO吸收和烟颗粒消光的相关处理,同时得到CO浓度和烟雾浓度.     

A case study on the determination of fog optical depth and liquid water path using AVHRR data and relations to fog liquid water content and horizontal visibility

An improved direct method is presented for the calculation of fog optical depth and liquid water path from fog top albedo using AVHRR channel 1. Fog top albedo is determined by means of a simple radiative transfer model under special consideration of radiometric corrections. By the conversion of channel I digital counts into a reflectance factor, a correction has to be performed, due to the degradation of channel 1 radiometer with time. By omitting atmospheric and anisotropy corrections, modal uncertainties in the calculations of fog top albedo in the order of ±25 per cent and ± 5 per cent were obtained. Assuming a homogeneous droplet distribution within fog layers at scan lime, a horizontal visibility was calculated from fog optical depth and fog geometrical thickness, whereas fog liquid water content was derived from liquid water path and fog thickness. Ground truth from high resolution transmiss-ometer observations showed an encouraging accuracy with a mean deviation between the observed and calculated visibility of about 56 m and a mean error in the determination of fog liquid water content of about 0·025 gm^?3.     

Guided local laplacian filter-based image enhancement for deep-sea sensor networks

This paper describes a novel method of enhancing deep-sea optical images using guided local Laplacian filter. Absorption and are two major distortion issues for deep-sea optical imaging. While light traveling through the water, light rays are scattered and absorbed depending on the wavelength. Scattering is caused by large suspended particles, as in turbid water that contains abundant particles, which causes the degradation of the captured image. Absorption corresponds to the varying degrees of attenuation encountered by light traveling in water at different wavelengths that causing ambient underwater to be dominated by a bluish tone. Our key contributions are proposed include a novel deep-sea imaging model to compensate for the attenuation discrepancy along the propagation path and an effective underwater scene enhancement scheme. The recovered images are characterized by a reduced noised level, better exposure of the dark regions, and improved global contrast where the finest details and edges are enhanced significantly.

     

In-situ optical monitoring of single-crystal silicon membrane etching

We present a simple yet efficient technique to monitor membrane thickness during etching of silicon in anisotropic etching bath. This technique uses a mechanical holder to protect the front side of the wafer and the measurement of light absorption to obtain remotely the thickness of a reference zone in the etched wafer. The original feature in our set-up is that we measure the absorption in two different bands of wavelength, one where the silicon is strongly absorbing and the other where it is not, improving the robustness of the measurement. Actually, this principle allows for effectively compensating the fluctuation in the optical path, and after calibration provides real-time information on the membrane thickness, which proves to be particularly useful for fabricating membranes below 40 \(\upmu\)m.     

Application of astigmatic method and snell’s law on the thickness and refractive index measurement of a transparent plate

In this study, a thickness and refractive index measuring system for the transparent plate has been proposed. The measuring system is composed of an astigmatic measurement module and a light spot measurement module using a DVD optical pickup, a laser diode and a quadrant photodiode detector. Both of the thickness and refractive index of a transparent plate are converted into the focusing error of DVD pickup based on astigmatic method and the light spot displacements based on snell’s law in our proposed system. The thickness and the refractive index are simultaneously calculated by means of two nonlinear formulas. The accuracy of the proposed system is 99 % verified by a height Gauge and the refractive index by the TF-166.     

Cost Efficient Fault Tolerant Design in Mesh Optical Networks with the Load Aware Method

With increasing wavelength capacity, the fault tolerant policy of the mesh optical network becomes much more important. To meet the survivability requirement, a set of cost efficient fault tolerant mechanisms are designed in this paper. The main objective is the minimization of the total number of required wavelengths. Furthermore, based on the method of the Integer Linear Program (ILP), shared-path protection and shared-link protection strategies are achieved, respectively. Moreover, the objective of minimizing the load imbalance is used to ensure the network resources utilized efficiently, and then the wavelength contention can be mitigated by selecting the working path and backup path reasonably. The results show that the survivability of the optical network can be guaranteed in a cost efficient manner.     

忆阻桥放大效应在光纤式结冰探测中的应用

鉴于双光路通道差动测量方法能够有效去除共模干扰,本文将新型电路元件—忆阻器与传统的光纤式结冰传感器相结合,提出了纳米级尺寸具有放大效应的忆阻桥网络结构,分析了忆阻桥的放大效应原理,实现了光电二极管光电流信号的放大,以桥臂忆阻阻值和感知忆阻两端电压作为传感输出,对冰层厚度进行探测。仿真实验结果表明：该双测量通道忆阻桥网络结构能够同时有效消除光路扰动和扩大结冰厚度的测量范围。     

基于TDLAS-WMS的近红外痕量CH_4气体传感器

为了对煤矿CH4气体进行实时监测,基于混合可调谐二极管激光吸收光谱(TDLAS)与波长调制光谱(WMS)的检测技术,采用中心波长为1.65μm的分布反馈(DFB)激光器,设计并研制出痕量CH4气体传感器。利用自主设计的DFB激光器温度控制器,通过调节激光器工作温度,进而使其发光光谱扫描CH4气体的吸收跃迁谱线。同时利用WMS检测技术将待测信号频率移至高频区,减小1/f噪声。利用该痕量CH4气体传感器,在被测气体体积分数为(0~106)×10-6的范围内,对二次谐波信号进行了提取。测试结果显示:在(0~106)×10-6范围内相对测量误差小于7%,检测下限为11×10-6。同时,研究人员可以通过更换其他波长的激光器,实现对其他气体的检测。     

海水光学硝酸盐传感器结构设计

根据海水硝酸盐紫外吸收光谱法测量原理,确定了海水光学硝酸盐传感器的组成与结构方式;根据海水环境应用要求,完成了传感器壳体选材与抗压计算;详细阐述了机械制作工艺测量光路同轴度的保障方法,并对传感器关键部分的密封方式、加工与装配精度进行了说明,实现了传感器水深100m的应用要求.     

一种内容完整的视频稳定算法

设计了一种基于可靠特征集合匹配的内容完整的视频稳定算法。为了避免运动前景上的特征点参与运动估计,由经典的KLT(Kanade-Lucas-Tomasi)算法提取特征点,而后基于特征有效性判定规则对特征点集合进行有效性验证以提高特征点的可靠性。利用通过验证的特征点对全局运动进行估计,得到精确的运动参数并据此对视频图像进行运动补偿。对于运动补偿造成的无定义区,首先计算当前帧的定义区与相邻帧的光流,以此为向导腐蚀无定义区;利用拼接的方法,填充仍为无定义区的像素。实验结果表明该算法对于前景物体运动具有较好的鲁棒性并能够生成内容完整的稳定视频序列。     

反射式红外甲烷传感器气室设计

设计给出一种稳定性好、灵敏度高的反射式红外甲烷传感器气室设计过程与测试结果。红外甲烷传感器基于色散型红外吸收光谱法的原理,利用非分光红外探测技术过滤甲烷气体的特征波长以外的光线,再采用双通道补偿技术对气室内部的甲烷气体体积分数进行检测。气室是红外探测器、传输光路、红外光源集成装配体,其结构和性能对器件性能至关重要。气室内壁设计成镀金的旋转抛物面,红外光经抛物面反射成近似平行的光束,该红外光束在气室内部传播过程被气室底盖反射到探测器,增加了甲烷气体的吸收光程,起到了提高气室的灵敏度的作用。设计完成后,经过甲烷环境的测试,反射式气室的稳定性、灵敏度、反应时间等都有良好的表现。