Accurate reflectance and optical fibre backscatter parameter measurements using an OTDR

A method for accurate reflectance measurement is described. The technique introduces a variable attenuator in a recirculating loop to calibrate the reflection provided by a fictitious reflector. A formula for this calibrated reflection is given. The device allows accurate measurements of the backscatter parameter of a fibre.<>     

Clinical application of an active electrode using an operationalamplifier

An active electrode (d10 mm, t6 mm) is presented, that functions as an impedance transformer (an input impedance > 10 G omega, an output impedance < 1 omega) by means of which we can derive surface EMG without any skin preparation and paste. This electrode was compared with a conventional one, and it was ascertained that the electrode could be replaced with the conventional one, and, moreover, it was preferable because it required less preparation time, and was less affected by environmental noise.     

用于真空在线测量的离轴非球面结构反射差分光谱仪设计与实现

基于旋转补偿器的反射差分光谱(RC-RDS)技术是 具有亚单层光学灵敏度的高精度表面表征方法,其全光谱快 速测量性能,特别适合在线检测。为满足真空在线测量的应用需求,综合考虑使用空间、工 作距离、光束 直径、光谱宽度和通光率等限制因素,提出了基于离轴抛物(OAP)反射镜的光学测头设 计方案,构建的测试样机 实现了有效工作距离大于50cm、光斑直径小于6.5mm和光谱范围涵盖280～825nm等性能。实验研究了超高 真空环境Cu(110) 样品在退火处理中的RDS,仪器详细记录了信号随温度的演 变过 程,测量精度优于3×10－4,表明新方案满足真空环境下表面 高灵敏光学测试的需求。     

Detection of ship wakes using an airborne magnetic transducer

Wakes induced by the motion of vessels may extend for tens of kilometers and exist for hours under certain conditions in the open sea. This provides a useful feature for long-range ship detection. The authors present a method for passively detecting a ship wake using measurements obtained by an airborne SQUID magnetic transducer that measures the first order gradients of the magnetic signature induced by the wake. Analytical formulas for wake magnetic gradients are derived to provide guidelines for using the airborne detector. They also derive bounds on the probability of wake detection for cross correlation and square-law detectors, which can be used to predict the expected performance. Numerical examples are used to demonstrate the applicability of their results     

The determination of cloud altitudes using GOME reflectance spectra: multilayered cloud systems

This paper is devoted to the application of the Semi-Analytical Cloud Retrieval Algorithm (SACURA) to the cloud-top height determination using data from the Global Ozone Measurement Experiment (GOME) instrument onboard Earth Remote Sensing satellite (ERS-2). In particular, measurements of the top-of-atmosphere reflectance in the oxygen absorption A-band are used. The technique is based on the asymptotic radiative transfer theory as applied to studies of the oxygen absorption bands in reflected light. Our approach is valid for optically thick clouds with cloud optical thickness larger than approximately 5. The accuracy of the algorithm is checked against independent retrieval techniques for completely cloudy pixels. In particular, the close coincidence with data obtained from the Along Track Scanning Radiometer (ATSR-2) onboard ERS-2 is found. Some results of retrievals using these different instruments disagree (up to 2 km). This is explained by the strong horizontal inhomogeneity of clouds under investigation, which is not accounted by the SACURA or, possibly, by well-known problems of infrared techniques as applied to low-level clouds. The effective cloud geometrical thickness l is also retrieved. This parameter is defined as the geometrical thickness of a vertically homogeneous cloud, which allows for the minimization of differences between observed and calculated top-of-atmosphere reflectance spectra. For inhomogeneous clouds, the value of l differs from a real cloud geometrical thickness, but it gives us an indication of the possible existence of the multilayered cloud system in the field of view of the optical instrument.     

Simulation method of reflectance measurement error using the OTDR

This letter presents an algorithm relating two different optical time-domain reflectometer (OTDR) reflectance measurement methods. From the impulse response of an OTDR, and the attenuation and reflectance values of a reflective event supplied by the OTDR operating according to a first classical implemented method, the algorithm allows the determination of the reflectance that would be measured according to a second more accurate method. Over a 10-dB comparison range the deviations between experimental results and those obtained with the proposed algorithm do not exceed 0.5 dB     

Detection and estimation using an adaptive rational function filter

Proposes a new nonlinear adaptive filter structure based on rational functions. There are several advantages to the use of this filter. First, it is a universal approximator and a good extrapolator. Second, it ran be trained by a linear adaptive algorithm, which makes it suitable for real-time adaptive signal processing. Third, it has a best approximation for a specified function. To demonstrate its utility as a tool for solving adaptive signal processing problems, the authors apply the adaptive rational function filter to the problem of estimation and detection. The estimation problem pertains to the direction of arrival (DOA) estimation problem in array signal processing. For the detection problem, the authors consider the detection of a weak radar target (a small piece of ice) in an ocean environment     

Classification of contamination in salt marsh plants using hyperspectral reflectance

In this paper, we compare the classification effectiveness of two relatively new techniques on data consisting of leaf-level reflectance from five species of salt marsh and two species of crop plants (in four experiments) that have been exposed to varying levels of different heavy metal or petroleum toxicity, with a control treatment for each experiment. If these methodologies work well on leaf-level data, then there is hope that they will also work well on data from air- and spaceborne platforms. The classification methods compared were support vector classification (SVC) of exposed and nonexposed plants based on the spectral reflectance data, and partial least squares compression of the spectral reflectance data followed by classification using logistic discrimination (PLS/LD). The statistic we used to compare the effectiveness of the methodologies was the leave-one-out cross-validation estimate of the prediction error. Our results suggest that both techniques perform reasonably well, but that SVC was superior to PLS/LD for use on hyperspectral data and it is worth exploring as a technique for classifying heavy-metal or petroleum exposed plants for the more complicated data from air- and spaceborne sensors.     

Detection performance of some nonparametric rank tests and an application to radar

The detection performance of some one-sample nonparametric rank tests for signals in Gaussian noise exhibiting a characteristic trend is presented in this paper for a finite number of observations and asymptotically. The tests considered are the Kendall tau, the Spearman rho, and a version of thec_1normal-scores test; both coherent and incoherent signal processing are considered. The asymptotic performance is determined through a simple extension of existing analytical results, whereas for a finite number of observations a direct Monte Carlo simulation is used. The latter requires a preliminary determination of false-alarm probability versus decision threshold. For the Spearman rho and thec_1tests an importance-sampling technique is used in a Monte Carlo simulation to determine the required results. Finally an application of the Kendall tau test to conventional radar is considered, in which the characteristic trend due to the amplitude modulation of the received train of echoes by the scanning of the antenna is used for detecting the presence of a target.     

多角度成像解析大豆冠层的二向反射特征

植被冠层二向性反射特征是定量遥感必须关注的一个问题。论文借助自主研发的多角度成像系统,在不同观测时间对不同种植密度下的大豆冠层进行多角度成像数据采集,通过对图谱合一的高光谱影像中大豆植株、土壤背景和阴影叶片进行逐步分离,对比分析纯大豆植被与植被-土壤混合冠层的二向反射（Bidirectional Reflectance, BR）变化特征,研究发现:在主平面观测时,土壤光谱去除后,即纯植被冠层反射率在前向观测时,随着天顶角的减小而增大,这不同于植被和土壤同时存在时的研究结果（BR 随着天顶角的增加而增大）;当观测方向由主平面的前向朝后向变动时,可见光和近红外波段的纯植被冠层反射率表现为逐步增大的趋势,这和土壤光谱去除前的变化趋势也不同;在垂直主平面观测时,去除土壤背景后的纯植被冠层反射率与混合植被反射率特征有相同的趋势,但在垂直主平面方向的对称性更强。上述结果在不同密度、不同观测时间的大豆冠层BR 特征有相近的趋势,这为多角度遥感的发展提供了必要的基础研究。     

重金属含量的高光谱建模反演:考古土壤中的应用

基于反射高光谱快速、无损的检测优势,以不同历史时期考古土壤作为光谱信息来源,应用相关分析和多元变量统计方法,构建了历史时期土壤重金属含量的高光谱反演模型.结果表明,Cd、Cr、Cu、Ni和Pb含量与原始光谱在400～550nm和1000～2500nm存在显著相关,微分转换有助于提取土壤中重金属元素信息.一阶微分光谱的多...     

The application of a geometric optical canopy reflectance model tosemiarid shrub vegetation

The Li-Strahler (1985) canopy model was tested, using SPOT HRV XS imagery, for semiarid shrub vegetation, based on 26 small (1-ha) sites in five classes of shrub vegetation, two dominated by tarbush, one by creosote bush, and two by mesquite. The model was driven by reflectance values derived from June and September imagery. While predictions of crown size and density for individual sites had a large average error of 35%, the predictions of shrub size and density were reasonably accurate when grouped by shrub class. The aggregated predictions for a number of stands within a class were accurate to within one or two standard errors of the observed average value. Accuracy was highest but predictions were biased for some classes (size was underestimated) when the nonrandom shrub pattern was characterized for the class based on the average coefficient of determination of density     

非均匀混浊介质多光谱反射成像的仿真与实验研究

提出了一种采集高动态范围多光谱反射率的实验方 法,并通过测量5个非均匀混浊介 质样品在全视场照射条件下和500~940nm波长范围内的反射图像数据 证明了本方法的可行性。同时 采用在辐射传输理论框架下建立的并行iMC蒙特卡罗仿真模型,通过使用漫反射标准板准确 记录入射光 束能量分布,输入至iMC仿真程序,获得可与反射率测量数据相比较的反射率仿真图像数据 。本文工 作为求解根据反射率确定非均匀混浊介质样品的光学特征与几何参数的逆问题提供了实验与 理论工具。     

Detection of dynamic strain using an SOA-fiber ring laser and an arrayed waveguide grating demodulator

In this letter, a fiber Bragg grating (FBG) dynamic strain sensing system using a semiconductor optical amplifier (SOA)-fiber ring laser (FRL) and an arrayed waveguide grating (AWG) demodulator is proposed. Due to the characteristics of SOA, it can act as the gain medium as well as light source. The AWG module is used as the wavelength demodulator. It is shown that SOA-based FRL sensors can accurately respond to 1.5 με dynamic strain signal with high frequency up to 120 kHz and almost no distortion in the waveforms. Experimental results show that the system can be used for acoustic testing, such as underwater ultrasonic detection and external impact monitoring. In addition, the simultaneous dual-channel demodulated system is investigated in detail to verify the multiplexing. This dynamic strain sensing system can be widely utilized in structural health monitoring because of its high stability, low cost and good multiplexability.     

Modeling of bipolar transistor using integral charge-control model with application to third-order distortion studies

A compact bipolar transistor model [integral charge-control model (ICM)] has recently been developed that intrinsically includes many high-level effects (for example, conductivity modulation, base push-out effect, Early effect, and impact ionization). This paper presents a detailed characterization of a high-frequency silicon bipolar transistor using the ICM, with sufficient accuracy to allow calculation of intermodulation distortion. A set of electrical measurements for extracting ICM model parameters is described, and the method of extraction is discussed in detail. Finally, calculated values of second- and third-order distortion produced signals are compared with measured values and are found to be in good agreement, which demonstrates the accuracy of the ICM.     

Knowledge worker performance analysis using DEA: an application toengineering design teams at Bell Canada

Knowledge worker productivity measurement is a very difficult undertaking, but implementing improvement suggestions is even more challenging for management. Data envelopment analysis (DEA) was used to examine the productivity, efficiency, and effectiveness of one such knowledge worker group-the Engineering Design Teams (EDT) at Bell Canada, the largest telecommunications carrier in Canada. Two functional models of the EDTs were developed and analyzed using input oriented constant returns to scale (CRS) and variable returns to scale (VRS) DEA models. First left free, the multipliers were then constrained using DEA Assurance Region models based on economic prices and managerial preferences. This study offers an excellent example where inefficient decision making units (DMU)-i.e., EDTs-could be made more efficient by improving their scale efficiency simply by reassigning work amongst the units. Bell divides its EDTs along provincial boundaries into Ontario and Quebec teams and each EDT is responsible for a specific geographic area in the province assigned to it. The results of the DEA analysis indicated that redrawing the geographical boundaries of the market area served by the EDTs could move both increasing and decreasing returns to scale EDTs toward CRS behavior. Substantial performance improvements are possible over the entire system, resulting in significant savings in costs without people dislocation or branch closings     

X-ray CT metal artifact reduction using wavelets: an application for imaging total hip prostheses

Traditional computed tomography (CT) reconstructions of total joint prostheses are limited by metal artifacts from corrupted projection data. Published metal artifact reduction methods are based on the assumption that severe attenuation of X-rays by prostheses renders corresponding portions of projection data unavailable, hence the "missing" data are either avoided (in iterative reconstruction) or interpolated (in filtered backprojection with data completion; typically, with filling data "gaps" via linear functions). In this paper, we propose a wavelet-based multiresolution analysis method for metal artifact reduction, in which information is extracted from corrupted projection data. The wavelet method improves image quality by a successive interpolation in the wavelet domain. Theoretical analysis and experimental results demonstrate that the metal artifacts due to both photon starving and beam hardening can be effectively suppressed using our method. As compared to the filtered backprojection after linear interpolation, the wavelet-based reconstruction is significantly more accurate for depiction of anatomical structures, especially in the immediate neighborhood of the prostheses. This superior imaging precision is highly advantageous in geometric modeling for fitting hip prostheses.     

Measurement method for output port reflectance of an erbium-doped fiber amplifier

A novel method to measure output port reflectance of an erbium-doped fiber amplifier (EDFA) was demonstrated. This technique was verified through simulating a "black box" EDFA with a reflector prior to the input port of a nonisolated EDFA.     

Compact high frequency true-time-delay beamformer using bidirectional reflectance of the fiber gratings

A compact high frequency true time delay (TTD) beamformer using bidirectional reflectance of the fiber gratings (FGs) is proposed. The FGs can be a set of fiber Bragg gratings (FBGs) or chirped fiber gratings (CFGs). The number and the length of the time delay lines are greatly reduced compared to the previous systems. A phase array antennas system using this TTD beamformer has many advantages including being compact, low requirement on the bandwidth of the tunable laser source and working at high microwave frequency. The proof-of-concept experiment results demonstrated the feasibility of the proposed scheme.     

Spectral fuzzy classification: an application

Geographical information (including remotely sensed data) is usually imprecise, meaning that the boundaries between different phenomena are fuzzy. In fact, many classes in nature show internal gradual differences in species, health, age, moisture, as well other factors. If our classification model does not acknowledge that those classes are heterogeneous, and crisp classes are artificially imposed, a final careful analysis should always search for the consequences of such an unrealistic assumption. We consider the unsupervised algorithm presented by A. del Amo et al. (2000), and its application to a real image in Sevilla province (south Spain). Results are compared with those obtained from the ERDAS ISO-DATA classification program on the same image, showing the accuracy of our fuzzy approach. As a conclusion, it is pointed out that whenever real classes are natural fuzzy classes, with gradual transition between classes, then its fuzzy representation will be more easily understood, and therefore accepted by users