差分吸收光谱测量臭氧浓度信号去噪的实验研究

对差分吸收光谱测量臭氧浓度信号去噪进行了实验研究。首先利用常用的小波变换、Savitzky-Golay滤波和傅里叶变换滤波这3种方法对臭氧的吸收光谱分别进行去噪处理,得到各自去噪后的吸收光谱,发现小波变换与Savitzky-Golay滤波可以很好地拟合特征吸收,傅里叶变换滤波稍差;然后,利用信噪比与均方根误差对所得光谱进行分析评价。实验结果表明:Savitzky-Golay滤波对信号去噪的效果最好,可优先应用于臭氧的光谱计量分析。     

基于离散频谱校正的差分吸收光谱数据处理方法研究

差分吸收光谱法(DOAS)常利用傅里叶变换滤波法来滤除光谱数据中的噪声, 但因其频率分辨率的限制,致其幅值误差较大,从而影响气体的测量精度。提出了一种离散频谱校正的差分吸收光谱数据处理方法,利用离散频谱主瓣内的谱线重心求出峰值的坐标,对幅值误差进行补偿,提高气体的测量精度。对不同浓度的SO2气体进行了浓度反演实验,结果表明:频谱校正法的反演误差小于5%,相对于传统的最小二乘法和傅里叶变换滤波法误差分别减少0.36%和0.88%;在谱线漂移两个采样间隔为0.28nm时,传统最小二乘法的平均误差为31.8%,频谱校正法的最大误差则为3.8%,效果明显优于前者。     

基于高温还原及差分吸收光谱监测烟气汞的实验研究

高温还原法在不需要催化剂的条件下可将烟气排放中的二价汞转化为零价汞,便于进行烟气总汞的监测。运用差分吸收光谱法（DOAS）反演出烟气汞浓度,与没有加高温装置的测量结果作对比,验证高温设备的适用性,并配比不同浓度的零价汞和二价汞进行混合实验。在传统的DOAS算法基础上,研究遗传算法、傅里叶变换滤波及积分面积法对烟气汞浓度的影响。实验结果表明:传统算法具有偶然性,整体误差大;傅里叶变换反演出的浓度误差较大;积分面积法较遗传算法误差偏低,整体波动也小,反演出的偏差最小为0.55%,适合用于反演低浓度排放的烟气汞测量。     

基于全相位FFT的油套环空中声速计算方法

油套环空中会产生各种噪声,使测得的接箍反射信号非常复杂,环隙中真实的声速则很难计算准确,可通过对原始接箍数据进行傅里叶变换的方法对声速进行估计,但是存在不可忽视的误差。全相位傅里叶变换是傅里叶变换的一种改进方法,能够获得更加准确的频率谱与相位谱。文章采用全相位快速傅里叶变换（all-phase Fast Fourier Transform,apFFT）得到原始接箍信号的频谱,然后通过该频谱进一步计算环隙声速,可得到更加准确的声速估计。通过对不同信噪比下的模拟接箍信号采用快速傅里叶变换（Fast Fourier Transform,FFT）和全相位快速傅里叶变换（apFFT）得到其频谱,可以验证apFFT具有很强的抑制频谱泄漏的能力,且抗噪性能比FFT更好。根据FFT谱和apFFT谱分别计算出声速并对比其精度,可以验证通过apFFT谱计算出的声速稳定性更好、精度更高。然后采用上述两种方法对不同深度井的实测接箍数据进行频谱分析与对比,验证了apFFT较之于FFT对谱峰位置的辨识能力更强,根据谱峰位置计算声速的准确性也将更高。     

DOAS技术中差分吸收光学密度获取方法

针对差分吸收光谱技术(DOAS)获取差分吸收光学密度(OD)的技术特点,本文提出采用自适应神经模糊推理系统(ANFIS)来逼近DOAS测量谱中慢变成分,并依次获得痕量气体差分吸收光学密度.该方法根据DOAS系统获得测量谱的特点进行自适应调整网络参数,因此能较精确地分离慢变部分和快变部分.利用SO<,2>样气进行实验,结果表明ANIFIS比多项式函数更为灵活.基于AINFIS网络获取的OD进行浓度反演,提高了DOAS反演精度.     

小波变换在混凝土冲击回波检测中的应用

采用冲击回波法检测混凝土厚度或者缺陷时,采用传统快速傅里叶变换方法,由于傅里叶变换的时移性以及信号中包含表面波和结构模态振动使得特征频率的提取较为困难。要解决特征频率提取受到干扰的问题,该文提出一种小波变换结合傅里叶变换的信号处理方法。首先对回波信号进行小波变换,得到信号时频图和小波边际谱,其次将小波边际谱与傅里叶谱相乘,得到增强傅里叶谱。结果表明:信号时频图可以确定表面波和模态振动的频率范围和时间跨度,增强傅里叶谱不仅可保证频率分辨率,而且抑制由于傅里叶变换的时移性产生的多个波峰,使得特征频率在频谱中更为清晰和准确,是一种适用于冲击回波检测的信号处理方法。     

评述:用自相关函数来分析和设计信号

在信号频谱分析的经典方法中,功率谱密度是从自相关函数作傅里叶变换来计算的。长期以来认为,比起平均运算来,数字傅里叶变换是更为繁复的处理。所以,傅里叶变换常常是在平均乘积的截出序列上实现的。截出通常是由有限的测量时间(改进统计稳定性),由可允许的计算时间或由于作波长测量时测量采样数目的有限所引起的。由于今天的数字傅里叶变换方法是种快速运算,所以目前人们计算功率谱密度所用方法是首先对所有数据点作变换,随后再平均。     

散斑分数傅里叶联合变换相关测量研究

提出数字散斑联合变换分数相关测量方法,利用分数相关可以锐化相关峰的作用,在数字散斑联合变换相关运算中用分数傅里叶变换代替傅里叶变换,提高测量精度。通过对散斑图像进行相位调制,有效地解决了分数傅里叶变换的移变性带来的谱移问题。编程模拟和对拉伸试件位移场测量的结果表明,只要选择合适的分数傅里叶变换级次和相位调制函数,可以使相关峰的半宽度从4～5pixel锐化到仅1pixel,得到优于傅里叶变换相关的理想输出。     

二维分布规则尺寸的激光在线测量方法的研究

本文对二维分布规则尺寸的激光在线测量进行了研究,提出了激光—傅里叶变换测量方法。与传统测量方法相比,它具有测量精度高,可靠性强、速度快并能实现自动在线测量的优点。该方法可用于能够产生规则傅里叶变换频谱的所有被测物体的几何量。     

傅里叶变换轮廓术测量方法的分析研究

对传统傅里叶变换轮廓术（FTP)、π相移法以及灰度图法测量结果进行对比分析。结果证明,随着被测物体高度梯度的增加,基于灰度图和π相移技术的改进傅里叶变换轮廓术取得了很好效果,特别是在梯度大于3的情况下适合采用π相移法,能更有效地提高傅里叶变换轮廓术的测量精度。     

Spherical particle size determination by analytical inversion of the UV-visible-NIR extinction spectrum

An analytic inversion method, based on the anomalous diffraction approximation for nonabsorbing spherical particles, was developed to retrieve the size distribution from the optical turbidity or extinction spectrum. This method makes use of a differential Fourier cosine transform approach and provides a simple and fast inversion by means of fast Fourier transform and the Savitzky-Golay filter. The applicability of this algorithm was tested on the extinction data generated by the Mie solution. The effects of noise, modality, band limits, and data set size were analyzed by comparison with simulated data. This method can be used to reconstruct the original monomodal and bimodal distributions from 10% noise-corrupted data. The peak position and ratio of peak heights can be recovered with 10% or less deviation. The experiments with latex spheres showed that the inversion result from this method compares favorably with that from the dynamic light scattering measurement.     

Superresolution of Fourier transform spectroscopy data by the maximum entropy method

The maximum entropy method (MEM) is applied to the interferogram data obtained using the technique of Fourier transform spectroscopy for estimating its spectrum with a resolution far exceeding the value set by the spectrometer. For emission line data, the MEM process is directly used with the interferogram data in place of the regular Fourier transformation process required in Fourier transform spectroscopy. It produces a spectral estimate with an enhanced resolution. For absorption data with a broad background spectrum, the method is applied to a modified interferogram which corresponds to the Fourier transform of the absorptance spectrum. Two results are presented to demonstrate the power of the technique: for the visible emission spectrum of a spectral calibration lamp and for the infrared chloroform absorption spectrum. Included in the paper is a discussion of the problems associated with practical use of the MEM.     

Monitoring O3 with solar-blind Raman lidars

The benefits of retrieving ozone concentration profiles by a use of a single Raman signal rather than the Raman differential absorption lidar (DIAL) technique are investigated by numerical simulations applied either to KrF- (248 nm) or to quadrupled Nd:YAG- (266 nm) based Raman lidars, which are used for both daytime and nighttime monitoring of the tropospheric water-vapor mixing ratio. It is demonstrated that ozone concentration profiles of adequate accuracy and spatial and temporal resolution can be retrieved under low aerosol loading by a single Raman lidar because of the large value of the ozone absorption cross section both at 248 nm and at 266 nm. Then experimental measurements of Raman signals provided by the KrF-based lidar operating at the University of Lecce (40 degrees 20'N, 18 degrees 6'E) are used to retrieve ozone concentration profiles by use of the Raman DIAL technique and the nitrogen Raman signal.     

Development of a measuring system for on-line in situ monitoring of composite materials manufacturing

A unique portable measuring system using an impedance spectroscopy method with a self-adapting frequency of measurement is introduced. The system is intended for the on-line in situ monitoring of composite materials curing under industrial conditions. The capabilities of the developed system are demonstrated through the results obtained from on-line in situ measurements of unreinforced thermosetting resin, as well as of composites under real manufacturing conditions. Observations are supported by the results of other established methods for determining the degree of curing: temperature-modulated differential scanning calorimetry (MDSC), Fourier transform infrared spectroscopy (FT-IR) and broadband dielectric spectroscopy (BDS). Compressive and bending tests were also carried out on manufactured composites removed at different stages of the post-curing phase. Due to the self-adapting frequency, the system has enhanced sensitivity in the post-cure phase when the diffusion-controlled reactions proceed and, therefore, is suitable also for the analysis of hard post-cure samples.     

Development of Fourier transform spectrometry for UV-visible differential optical absorption spectroscopy measurements of tropospheric minor constituents

Concentration measurements of trace gases in the atmosphere require the use of highly sensitive and precise techniques. The UV-visible differential optical absorption spectroscopy technique is one that is heavily used for tropospheric measurements. To assess the advantages and drawbacks of using a Fourier transform spectrometer, we built a differential optical absorption spectroscopy optical setup based on a Bruker IFS 120M spectrometer. The characteristics and the capabilities of this setup have been studied and compared with those of the more conventional grating-based instruments. Two of the main advantages of the Fourier transform spectrometer are (1) the existence of a reproducible and precise wave-number scale, which greatly simplifies the algorithms used to analyze the atmospheric spectra, and (2) the possibility of recording large spectral regions at relatively high resolution, enabling the simultaneous detection of numerous chemical species with better discriminating properties. The main drawback, on the other hand, is due to the fact that a Fourier transform spectrometer is a scanning device for which the scanning time is small compared with the total measurement time. It does not have the signal integration capabilities of the CCD or photodiode array-based grating spectrographs. The Fourier transform spectrometer therefore needs fairly large amounts of light and is limited to short to medium absorption path lengths when working in the UV.     

紫外吸收光谱法在线测量SO3的实验研究

基于紫外吸收光谱法对SO₃的在线测量进行了实验研究,搭建了SO3气体发生系统。为提高检测精度,探究了去除测量过程中的各种干扰因素。SO₃与SO₂的特征吸收波段重叠严重,通过合理选择特征吸收波段和光谱反演策略最大程度地去除SO₂对SO₃测量的影响。研究中采用标准曲线法结合单波长法、双波长法和积分光谱法建立了标准曲线。结果表明:积分光谱法的测量误差最小,可优先应用于SO3排放的在线光谱计量分析。     

波导式气体吸收池时间响应特性

波导式光学吸收池在气体浓度测量等领域有广泛的应用前景.本文理论分析了在普通扩散环境和压差环境下波导式光学吸收池的时间响应机理和特性,并搭建了相应的传感系统,优化系统结构进行了实验验证.通过对低浓度的甲烷和甲苯气体的测量实验,验证和修正了响应时间的理论模型.实验结果表明,优化系统在可以大幅降低响应时间的同时,保持较高的灵敏度,为波导式吸收池的设计与优化提供了重要的参考.     

频谱分析型激光测速系统

提出一种结构简单、测量精度高的频谱分析型激光测速系统。该系统采用双入射光差动型 光路,利用硬件采集多普勒电压值和包络起始时刻送入PC机,通过软件加窗、补零、FFT谱分析及相位差频谱校正处理,实现多普勒频率值的计算、细化,最终得到相关速度结果。非对称突扩管道流速测量的应用证明该系统是可行的。