星载高光谱红外传感器反演大气痕量气体综述

利用遥感监测全球尺度上的痕量气体分布以及动态变化,对于理解对流层大气化学以及温室气体的源与汇具有重要的意义。本文首先介绍了国内外用于痕量气体探测的高光谱红外传感器的发展,由辐射传输方程出发分析了大气痕量气体遥感反演的特点,从前向模型、先验知识和最小化代价函数方案三个方面阐述了大气痕量气体遥感反演方案,最后指出了目前利用星载高光谱红外遥感数据反演大气痕量气体存在的一些问题以及可能的解决方案。     

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。     

基于光声光谱技术的多组分气体探测研究进展

多组分痕量气体检测在工业、军事、农业和医疗等领域均有着重要的研究和应用价值。高性能光声光谱技术因其灵敏度高、响应快、选择性高及非接触式实时连续测量等优点受到人们的青睐。本文首先对多组分气体监测需求和光声光谱技术的主要优势和基本原理进行阐述;然后从光源分类的角度出发,介绍了现有多组分气体测量技术的最新研究进展,概括光声光谱中常用的探测方式,包括多路复用技术和干涉型傅里叶变换红外光谱等,并对其具体的适用范围和优缺点进行了对比分析。同时,针对实际应用环境中气体传感系统主要存在的光谱干扰和吸附效应的问题,介绍了相应的解决方法。最后,对光声光谱多组分探测方法的未来发展方向进行了总结和展望。     

应用TDLAS探测气体的误差分析与补偿研究

针对基于可调谐二极管激光吸收光谱技术(TDLAS)的气体体积分数检测系统,介绍了TDLAS探测气体体积分数的原理;详细分析了测量误差的影响因素;研究了将所测得的吸收谱线扣除背景谱线,对采集到的二次谐波信号采用最小二乘波形拟合的信号处理方法。这种方法可以有效地抑制噪声干扰,提高探测灵敏度。     

瓦斯遥测关键技术现状与发展方向

介绍了基于可调谐半导体激光吸收光谱的瓦斯遥测关键技术——可调谐半导体激光技术、信号降噪技术、痕量气体检测技术的应用现状,指出了瓦斯遥测关键技术中存在可调谐半导体激光器性能不稳定、瓦斯遥测距离短、信号降噪效果较差、痕量气体检测误差大等问题,提出了研发高性能可调谐半导体激光器、研究非线性和非稳定性信号降噪算法、设计适用于井下的数字锁相放大器是瓦斯遥测关键技术的发展方向。     

利用光纤和OMA研究A1等离子体的空间分辨光谱

利用光纤和光学多道分析仪(OMA)检测激光诱导产生的A1等离子体发射光谱,可使实验系统的光路调试较为简便,同时可方便地检测距靶面不同位置处的谱讯号.本文分别研究了在空气(Air)、氮气(N2)和氩气(Ar)环境气体下谱线强度空间分布的不同特征,并研究了不同环境气体气压下谱线宽度随靶距离变化的情况,对激光等离子体的诊断具有重要意义.     

基于数字锁相放大器的甲烷谐波检测虚拟系统

基于甲烷气体的谐波检测技术,利用数字锁相放大器SR830检测甲烷气体吸收谱线的一、二次谐波,在LabVIEW虚拟仪器设计平台上设计甲烷浓度谐波检测虚拟仪器系统,实现了对数字锁相放大器的远程控制和对数据的采集与处理;实验结果与理论模型相吻合,充分验证了采用数字锁相放大器检测甲烷气体浓度可以精确的提取出谐波信号,获得较好的信噪比。     

痕量爆炸物快速检测仪在安徽通过验收

中国科学院安徽光机所成功研制一种用于痕量爆炸物检测的新型离予迁移谱快速检测仪,并通过了国家科研和安全等主管单位组成的专家组验收。     

锁相放大技术在光学式甲烷气体传感器中的应用

设计了一种基于近红外可调谐半导体激光吸收光谱的光学式甲烷气体传感器,传感器针对甲烷气体位于1653.722nm处的吸收谱线,应用锁相放大技术提取微弱的一次谐波幅度信号,实现对气体浓度的测量。重点分析了在光学式甲烷气体传感器中应用锁相放大的原理及关键技术。结果表明该传感器响应时间为10s,测量精度可达0.02%VOL。     

基于吸收光谱乙炔气体浓度在线检测系统的研究

可调谐二极管激光吸收光谱技术是利用二极管激光器的波长调谐特性,获得被选定的待测气体特征吸收谱线的吸收光谱,从而对待测气体进行定性或定量分析技术,与多次反射池相结合,利用谐波检测技术对所提取的微弱信号进行处理,设计了一套远距离在线测量乙炔气体监测系统,经过系统实验,能准确、快速地完成乙炔气体浓度的监测。     

Optical parametric oscillators in lidar sounding of trace atmospheric gases in the 3–4 μm spectral range

Applicability of a KTA crystal-based laser system with optical parametric generation to lidar sounding of the atmosphere in the spectral range 3–4 μm is studied in this work. A technique developed for lidar sounding of trace atmospheric gases is based on differential absorption lidar (DIAL) technique and differential optical absorption spectroscopy (DOAS). The DIAL-DOAS technique is tested to estimate its efficiency for lidar sounding of atmospheric trace gases.     

Outgoing longwave flux estimation: improvement of angular modelling using spectral information

A radiance-to-flux conversion is needed to estimate radiative fluxes at the top of the atmosphere from directional measurements made by broadband (BB) radiometers on satellites. Such a conversion is known to be one of the major sources of error in the resulting instantaneous shortwave and longwave fluxes. This paper analyzes the possibility to improve the radiance-to-flux conversion for the longwave radiation when spectral information about the radiation is available through a set of narrow-band (NB) measurements. The study is based on a database of spectral radiance fields at the top of the atmosphere built using radiative transfer computation. The analysis of this database shows that there exists a certain degree of correlation between the angular and the spectral behaviors of the radiation field. According to the type and the accuracy of the spectral information, this correlation allows a 25-55% reduction of the error introduced by the radiance-to-flux conversion with respect to a simple model that uses only broadband information. The method discussed in this paper might be used when broadband radiometer and spectral imager data are available together like the combination of Geostationary Earth Radiation Budget (GERB) and Spinning Enhanced Visible and Infrared Radiometer Imager (SEVIRI) or the combination of CERES and MODIS.     

组合分析蚀变信息提取方法研究

目前主成分分析法、比值法、光谱角制图法等已广泛应用于遥感矿化蚀变信息提取中,且取得了很好的效果。根据研究区遥感数据特点,采用比值与主成分组合分析的方法,结合FLAASH大气校正、中值滤波以及彩色密度分割等图像处理方法,对新疆且末地区ASTER数据进行蚀变信息提取。经USGS标准矿物波谱库中典型矿物光谱的验证,组合分析方法能够去除数据冗余和噪声,有利于各类蚀变信息的提取。     

Downscaling of passive microwave soil moisture retrievals based on spectral analysis

The retrieval of soil moisture from passive microwave remote-sensing data is presently one of the most effective methods for monitoring soil moisture. However, the spatial resolution of passive microwave soil moisture products is generally low; thus, existing soil moisture products should be downscaled in order to obtain more accurate soil moisture data. In this study, we explore the theoretical feasibility of applying the spectral downscaling method to the soil moisture in order to generate high spatial resolution soil moisture based on both Moderate Resolution Imaging Spectroradiometer and Fengyun-3B (FY3B) data. We analyse the spectral characteristics of soil moisture images covering the east-central of the Tibetan Plateau which have different spatial resolutions. The spectral analysis reveals that the spectral downscaling method is reliable in theory for downscaling soil moisture. So, we developed one spectral downscaling method for deriving the high spatial resolution (1 km) soil moister data from the FY3B data (25 km). Our results were compared with the ground truth measurements from 15 selected experimental days in 16 different sites. The average coefficient of determination (R²) of the spectral downscaling increased nearly doubled than that of the original FY3B soil moisture product. The spectral downscaled soil moister data were successfully applied to examine the water exchange between the land and atmosphere in the study regions. The spectral downscaling approach could be an efficient and effective method to improve the spatial resolution of current microwave soil moisture images.     

Semiclassical Trace Formulae and Eigenvalue Statistics in Quantum Chaos

A detailed discussion of semiclassical trace formulae is presented and it is demonstrated how a regularized trace formula can be derived while dealing only with finite and convergent expressions. Furthermore, several applications of trace formula techniques to quantum chaos are reviewed. Then local spectral statistics, measuring correlations among finitely many eigenvalues, are reviewed and a detailed semiclassical analysis of the number variance is given. Thereafter the transition to global spectral statistics, taking correlations among infinitely many quantum energies into account, is discussed. It is emphasized that the resulting limit distributions depend on the way one passes to the global scale. A conjecture on the distribution of the fluctuations of the spectral staircase is explained in this general context and evidence supporting the conjecture is discussed.     

Refinement of wavelength calibrations of hyperspectral imaging data using a spectrum-matching technique

The concept of imaging spectrometry, or hyperspectral imaging, is becoming increasingly popular in scientific communities in recent years. Hyperspectral imaging data covering the spectral region between 0.4 and 2.5 μm and collected from aircraft and satellite platforms have been used in the study of the earth's atmosphere, land surface, and ocean color properties, as well as on planetary missions. In order to make such quantitative studies, accurate radiometric and spectral calibrations of hyperspectral imaging data are necessary. Calibration coefficients for all detectors in an imaging spectrometer obtained in a laboratory may need to be adjusted when applied to data obtained from an aircraft or a satellite platform. Shifts in channel center wavelengths and changes in spectral resolution may occur when an instrument is airborne or spaceborne due to vibrations, and to changes in instrument temperature and pressure. In this paper, we describe an algorithm for refining spectral calibrations of imaging spectrometer data using observed features in the data itself. The algorithm is based on spectrum-matching of atmospheric water vapor, oxygen, and carbon dioxide bands, and solar Fraunhofer lines. It has been applied to real data sets acquired with airborne and spaceborne imaging spectrometers.     

Radiometric normalization for change detection in peatlands: a modified temporal invariant cluster approach

Radiometric normalization is a vital stage in any change detection study due to the complex interactions of radiance and irradiance between the Earth's surface and atmosphere. Compensation for variables such as sun's angle, surface profile, atmospheric conditions, and sensor calibration coefficients are essential in achieving a radiometrically stable data base of multi-temporal, multi-spectral imagery for a change detection study. In this study, five Landsat Enhanced Thematic Mapper Plus (ETM+) images taken over the east coast of Ireland in 2001 were geometrically corrected and topographically normalized for further processing and analysis. Assessment of various vegetation indices showed that the enhanced vegetation index 2 (EVI2) gave the highest accuracy in identifying the various vegetation types and habitats in the Wicklow Mountains National Park. The initial analysis of radiometric normalization with temporal invariant clusters (TICs) gave poor results due to the spectral heterogeneity of urban pixels within each image. A revised TIC subset normalized method was developed using regional growth parameters in urban environments to limit the spatial and spectral extent of pixels used in the TIC scene normalization process. Correlation analysis between the TIC-subset-normalized ETM+ data and Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) absolute corrected data produced coefficient of determination (R²) values between 0.88 and 0.98. Such results demonstrated the robustness of the TIC subset normalization procedure when correcting for atmospheric variability between images while maintaining spectral integrity. Statistical analysis on master slave and TIC-subset-normalized slave data using cumulative distribution curves derived from image histograms showed an 86.93% reduction in the maximum difference between master and slave data due to the TIC subset normalization process. This procedure of radiometric normalization is suitable in landscapes with a low density of spectrally stable targets.     

Multi‐sensor data fusion and comparison of total column ozone

With many remote‐sensing instruments onboard satellites exploring the Earth's atmosphere, most data are processed to gridded daily maps. However, differences in the original spatial, temporal, and spectral resolution—as well as format, structure, and temporal and spatial coverage—make the data merging, or fusion, difficult. NASA Goddard Earth Sciences Data and Information Services Center (GES‐DISC) has archived several data products for various sensors in different formats, structures, and multi‐temporal and spatial scales for ocean, land, and atmosphere. In this investigation using Earth science data sets from multiple sources, an attempt was made to develop an optimal technique to merge the atmospheric products and provide interactive, online analysis tools for the user community. The merged/fused measurements provide a more comprehensive view of the atmosphere and improve coverage and accuracy, compared with a single instrument dataset. This paper describes ways of merging/fusing several NASA Earth Observing Systems (EOS) remote‐sensing datasets available at GES‐DISC. The applicability of various methods was investigated for merging total column ozone to implement these methods into Giovanni, the online interactive analysis tool developed by GES‐DISC. Ozone data fusion of MODerate resolution Imaging Spectrometer (MODIS) Terra and Aqua Level‐3 daily data sets was conducted, and the results were found to provide better coverage. Weighted averaging of Terra and Aqua data sets, with the consequent interpolation through the remaining gaps using Optimal Interpolation (OI), also was conducted and found to produce better results. Ozone Monitoring Instrument (OMI) total column ozone is reliable and provides better results than Atmospheric Infrared Sounder (AIRS) and MODIS. However, the agreement among these instruments is reasonable. The correlation is high (0.88) between OMI and AIRS total column ozone, while the correlation between OMI and MODIS Terra/Aqua fused total column ozone is 0.79.     

Spectral norm and trace bounds of algebraic matrix Riccatiequations

Upper bounds on spectral norm and trace for the solution of continuous algebraic matrix Riccati equations are proposed. The proposed bounds are based on a form of the general analytic solution. It is shown that, in many cases, the spectral norm and the trace bounds are better than other results     

Mapping sediment-laden sea ice in the Arctic using AVHRR remote-sensing data: Atmospheric correction and determination of reflectances as a function of ice type and sediment load

Exploiting the fact that the spectral characteristics of light backscattered from sediment-laden ice differ substantially from those of clean ice and that sediment tends to accumulate at the ice surface during the first melt season, remote-sensing techniques provide a valuable tool for mapping the extent of particle-laden ice in the Arctic basin and assessing its particulate loading. This study considers two fundamental problems that still need to be addressed in order to make full use of satellite observations for this type of assessment: (i) the effects of the atmosphere on surface reflectances derived from radiances measured by the satellite sensor need to be quantified and ultimately corrected for, and (ii) the spectral reflectance of the ice surface as a function of particle loading and sub-pixel distribution needs to be determined in order to derive quantitative estimates from the at-sensor satellite signal. Here, spectral albedos have been computed for different ice surfaces of variable sediment load with a radiative transfer model for sea ice coupled with an optical model for particulates included in sea ice. In a second step, the role of the atmosphere in modulating the surface reflectance signal is assessed with the aid of an atmospheric radiative transfer model applied to a “standard” Arctic atmosphere and surface boundary conditions as prescribed by the sea ice radiative transfer model. A series of sensitivity studies helps assess differences between top-of-the-atmosphere and true surface reflectance and has been utilized to derive a look-up table for atmospheric correction of Advanced Very High Resolution Radiometer (AVHRR) data over sediment-laden sea ice surfaces. In particular, the effects of solar elevation, viewing geometry, and atmospheric properties are considered. The atmospheric corrections are necessary for certain geometries and surface types. Large discrepancies between raw and corrected data are particularly evident in the derived coverage of clean ice and ice with small sediment loading.