Optical fiber sensors are of great and increasing interest for the measurement of physical parameters such as acoustic and electro-magnetic fields. The germane fiber properties, namely, ruggedness, small size, and dielectric construction, are, however, equally desirable for industrial and laboratory mechanical metrology. This review contains a classification of the types of metrological sensors possible with fibers, including applications to measurement of submicroscopic to kilometer dimensions.

Interlaboratory comparisons using common (reference) materials of known composition are an established means for assessing overall measurement precision and accuracy. Intercomparisons based on common data sets are equally important and revealing when one is dealing with complex chemical patterns or spectra requiring significant numerical modeling and manipulation for component identification and quantification. Two case studies of "chemo-metric intercomparison" using simulation test data (STD) are presented, one comprising STD vectors as applied to nuclear spectrometry and the other STD data matrices as applied to aerosol source apportionment. Generic information gained from these two exercises included (a) the requisites for a successful STD intercomparison (including the nature and preparation of the simulation test patterns); (b) surprising degrees of bias and imprecision associated with the data evaluation process per se; (c) the need for increased attention to implicit assumptions and adequate statements of uncertainty; and (d) the importance of STD beyond the intercomparison, i.e., their value as a research tool for improv-ing the state of the pattern recognition art.

An overview is presented of an expert system approach to the automatic interpretation of recordings of the electrical activity of the brain (electroencephalogram, or EEG). The method consists of a quantification module and a rule-based expert system. Quantification is done by means of autoregressive spectral estimation. It was found that the rule-based system correctly classified 93% of EEGs taken from renal patients, and a 70% agree-ment was found between the system and an electroencephalographer in an experiment aimed at determining the depth of sleep in normal subjects. An indication of how this approach may be used for spectral pattern recognition concludes this paper.

During the past few years it has been demonstrated that linkage of multiple spectrometry systems with gas chromatography (GC) offers significant advantages for structural analysis of mixture components as they are sepa-rated. In the work to be described, a Fourier transform mass spectrometer (FTMS) has been linked in parallel with a Fourier transform infrared (FTIR) spectrometer for concurrent analysis of GC eluants from a fused silica capillary column. This system provides FTIR, electron impact, and chemical ionization mass spectral analysis of each mixture component as it emerges from the GC. Furthermore, mass measurement accuracy in the low ppm range in the absence of calibrant is made possible by the FTMS. Effective use of the com-plementary information obtained is shown to produce more reliable analytical performance than for any individual measurement.

Image degradation caused by relative motion between an object and an imaging system (such as a camera with its platform) is detrimental to precision measurements of the image. In this paper, principal modes of relative motion are identified. The discussion, however, concentrates on the systematic motions, translatory and rotatory. Various known analogical approaches to compensate for image motion are cited. An analytical/computational approach is presented. This considers the three-dimensional transformation relationship between the image and the object, known as the collinearity condition. The standard forms of collinearity equations are presented. Augmentation of these equations for both translatory and rotatory motions is expounded. With the increasing use of high-speed computers (and analytical plotters in the realm of photogrammetry), this approach appears to be more cost-effective and seems to yield better precision than other approaches that concentrate on analogical corrections to the image.

This paper is an overview of electro-optical methods for generating a sequence of pixel clocks related to the angular rotation of a scanner excited in a sinusoidal motion. The emphasis is on the methods of synchronizing the clock generator to the scanner motion and on the trade-offs between scanner frequency, pixel placement accuracy, and the total system resolution. The methods are suitable for data input and output applications. Both digital and analog implementations of a clock generator are explored, and the drift and stability issues examined. Scan field distortion correction capabilities are also detailed.

A simplified static multi-interferogram evaluation method is proposed. With its aid the absolute fringe order number can be determined in the absence of the zero-order fringe. The method can be applied to measuring 3-D displacement due to static/dynamic load in industrial environments. Data needed for determining 3-D displacement are stored on four independent interferograms. The recording holographic interferometer is presented. An experimental investigation of a hydraulic press model has been performed to illustrate the effectiveness of the proposed technique.

A new image enhancement technique has been applied to enhance Landsat-4 Thematic Mapper (TM) thermal infrared (IR) imagery and has improved its effective ground resolution from 120 m to 30 m. The technique is based on an adaptive multiband least squares (LS) method for computing an optimal image estimate from reference images, and a frequency domain replacement step. The approach relies on the assumption that at a sufficiently small resolution registered TM imagery data are locally correlated across the bands. Using the local correlation property, visible and IR reference bands are used to predict the thermal IR image data. The prediction estimate is then used to augment the spatial high frequency information in the original thermal data. Preliminary experiments enhancing 120 m IR imagery (simulated degradation) to 30 m resolution show a signal-to-noise ratio improvement of 19 dB.

Median filtering of digital imagery is known to remove noise while preserving edges. However, it is not evident that median filters facilitate further machine processing such as machine recognition. In this paper, median filtering and median/inverse filtering are explored and evaluated based on their performances in machine recognition. Furthermore, this work is also aimed at gaining insight into the design of practical median-filter preprocessors for automatic pattern recognition systems. The design of a median filter depends solely on the selection of window shape and size. For this study, the median-filter window shape and size were determined empirically based on the performance in enhancing automatic pattern recognition. The results show that median filtering is most effective for enhancing machine recognition in cases in which images are corrupted by impulse-type noise alone or in conjunction with blurs. It is not as effective when images are corrupted by white Gaussian noise and/or in combination with blurs; however, median/inverse filtering does enhance machine recognition in these cases.

In many different fields of information processing, such as medical or aerial image processing, computer aided design or manufacturing (CAD/CAM), and flight simulation or control activities, there exists an increasing need for display of true three-dimensional data. In this paper a screen is proposed that composes a 3-D image from information of different depth planes (image slices). The angular selectivity of holographic elements in a thick phase material (such as dichromated gelatin) is used to combine the image slices, which are projected from different directions to a 3-D image. This screen has a high light efficiency, uses no mechanically moving parts, and can be addressed in real time. The principle of the setup will be described, and some preliminary results will be presented.

A measuring system combining subnanosecond laser-induced fluorescence with microscopic signal detection was installed and used for diverse projects in the biomedical and environmental fields. These projects range from tumor diagnosis and enzymatic analysis to measurements of the activity of methanogenic bacteria, which affect biogas production and waste water cleaning. The advantages of this method and its practical applicability are discussed.

A new approach to high speed combustion photography consists in viewing the fuel injection and combustion process through specially designed endoscopes. Compared to conventional film techniques, the use of an endoscope as a photography system requires that very small windows be fitted into the cylinder head of the engine, thus causing minimal interference with the combustion process. The windows are made of fused silica to withstand the high gas temperature and pressure inside the combustion chamber of a diesel engine. The outcoming image from the endoscope is transmitted to the camera through several rigid optical relay systems, interconnected with rotating optical joints. A flash bulb located behind a second window is used to illuminate the nonluminous process of fuel spray formation during the ignition delay period.

The issue of pointing errors between satellite-borne, free-space optical communication systems is examined. The single-axis pointing error distribution is described as a Gaussian function and is used to define a probability of burst error for the pointing subsystem. A relationship between the rms standard deviation of the pointing error distribution, the probability of burst error, and the Airy far field beamwidth is deduced. It is shown that the system beamwidth and antenna diameter are limited by the probability of burst error. Additionally, it is found that typical terminal designs have less temporal communication system availability than one specifically designed to account for the influence of burst errors.

Two applications of thermography for testing and development of turbomachinery components are described: (1) Fabrication defects in the cooling system of internally cooled turbine blades are detected by transient heating of the blade and measurement of its surface temperature distribution by an infrared imaging system. Defects like blocking, narrowing, widening, and mispositioning of cooling channels can clearly be identified by the disturbance of the transient surface temperature distribution of the blade. (2) To improve the cooling configuration of turbine blades, the cooling effectiveness over the total blade surface must be determined under test conditions similar to those in the turbomachine. The infrared measurement of blade surface temperature distributions in a hot air cascade and the method to correct the infrared intensities for radiation reflected at the measuring surface are illustrated in an example.

A microcomputer-based digital image processing system has been developed to count and size laser-generated small particle images. Processing rates of 5 to 600 frames per minute were achieved by utilizing a real-time digital image processor. Particles from 7 to 700 µm in the plane of focus were counted and sized. A major emphasis in this work was to determine the basic problems and limitations involved with using a digital image processing scheme to accurately size particles. Areas that were investigated include the effect of the threshold level on measured particle size, particle boundary diffraction gray-level gradients, and geometric nonlinearities introduced by the vidicon camera. A Laser Electro-Optics Ltd. calibration reticle containing simulated particles from 5.29 to 92.75 µm in diameter was used as the basis for an in-depth calibration process. It was determined that various inherent problems with image processing systems limit their accuracy unless compensation is made. Decalibration techniques were used to correct for these inaccuracies. After correction, an average error of less than 1.0% was found for 25 to 100 µm particles. A 2.8% error was found in the experimentally determined distribution of 52.8 µm polystyrene microspheres.

Multianode microchannel array detector systems with formats as large as 256 x 1024 pixels are currently under evaluation in the laboratory. Performance data recorded with sealed ultraviolet and visible-light detector tubes have shown that the detector systems have unique characteristics that make them complementary to photoconductive ar-ray detectors, such as charge-coupled devices, and superior to alter-native pulse-counting detector systems employing high-gain microchannel plates.

An overview of IR fibers is presented, including prospective crystalline and vitreous materials; fiber fabrication methods such as drawing from preforms, crucible draw, pedestal growth, and extrusion; and applications such as ultralong repeaterless links, IR imaging, and IR power transmission.

It is demonstrated that the temperature of a thermal radiator can be determined without prior knowledge of the emissivity of the source by curve-fit-ting techniques using multiple spectral radiance measurements. This new passive measurement technique assumes only that a smooth function exists between spectral emissivity and wavelength. The spectral radiance values are fitted to a Planck radiation law relation to yield the temperature of the source. Error analysis shows that relative errors in the temperature measurements are generally an order of magnitude less than in the spectral radiance measure-ments and in the simultaneously calculated spectral emissivity values. Computer simulations are included that show the effects of varying different parameters, such as the number of data pairs, the wavelength range, the spectral emissivity behavior, the source temperature, and the measurement noise, on the accuracy of the temperature determination. Experimental confirmation of this technique is presented, showing temperature measurements within 1% of the actual temperatures on a platinum surface within a temperature range of 1273 to 1724 K.

When holography is applied outside the laboratory, some well-known problems are encountered: vibrations, rigid-body motion, and stray daylight. Pulsed holography can overcome the difficulties with vibrations, but the other problems are less easily solved. When the object area to be holographically tested is small, a very simple and conve-nient method may be employed, which was described independently by Boone (1974) and Neumann and Penn (1975). They fixed the hologram holder rigidly to the object under test, thus avoiding rigid-body motion of the object with respect to the hologram. In a similar configuration Denisyuk reflection holograms are made without any necessity of darkening the environment. The authors believe that the main reason this technique is not widely used is due to difficulties generally encountered in processing the Denisyuk hologram to good quality. This paper describes a simple processing technique that results in high quality reflection holograms that may be analyzed by microscope up to interference fringe densities of about 30 fringes/mm. As examples, the results of a projectile impact study and the study of early fatigue crack detection in a critical airplane structure are presented.

A quantitative shadow method was developed and tested by measuring the one-dimensional refractive index distribution of a polished slab of gradient index glass. Tests made on the known glass sample showed that a one-dimensional index distribution can be measured by shadowgraphy to better than 1% accuracy. The method uses simple optics and can easily be auto-mated to perform rapid measurements. Extension of the shadow method to more general distributions requires making many traverses of the refractive index distribution with a narrow sheet of light.

The versatility of the laser-heated pedestal growth method for producing a wide range of compounds in single-crystal fiber form is discussed, along with some potential applications. Some preliminary results on the growth of single-domain LiNbO3 crystals, and crystals of BaF2 and CaF2, sapphire, and several laser materials are discussed.

Present and future markets for photo-voltaic devices are discussed in detail. It is pointed out that such devices are already a major industry rather than just a hope for the future. Existing commercial devices and other near-term possibilities are briefly described, and some of the companies involved in research, development, and / or commercial production associated with each class of material are identified.

The intrinsic and extrinsic processes that limit light propagation at low powers in infrared optical fibers are described. A theoretical V-curve is constructed, and specific absorption coefficients and the vibrational absorption of various impurities are tabulated versus frequency. The limitation imposed by parametric and nonlinear processes at high powers is described. Values for the critical powers for these processes in typical infrared optical fibers are presented.

At the meeting of the SPIT Board of Governors held in Arlington, Virginia, this past spring, a great deal of time was devoted to concerns over the government's involvement in various aspects of the Society's affairs. There were distractions related to technology transfer, distractions due to the establishment of separate export control sessions at the technical symposium, and distractions caused by the presence of the media at the symposium.

Volume 5 of the series Laser Applications deals with recent applications of laser technology. Previous volumes of this series have dealt mainly with physical measurements and physical processes using lasers; in contrast, Vol. 5 covers several chemical aspects of laser applications. The use of lasers in spectroscopy and diagnostics, especially in chemical applications, has been well documented. However, the initial promise for the use of lasers in chemical processing has been slow to come to fruition; it is perhaps a testament to recent

Many fields of scientific research derive their excitement from the fact that they are totally new avenues of investigation. Other areas are remarkable for their longevity and their ability to continually generate new developments. The topic of this special issue, 3-D Sensing for Inspection, falls in the latter category. Three-dimensional sensing has been an active area of study since the earliest scientific endeavors in optics. The collection of papers in this issue attests to the continued vitality of the field today. The reason for this success perhaps stems from the fact that it is being driven by critical fundamental scientific needs as well as by ever-expanding technological applications. The papers assembled here address both of these areas.

Heterodyne techniques have proved to be a very sensitive tool for measuring minute dynamic phase changes imposed on an optical beam. In this paper, we review the application of this powerful tool to the area of micrometrology. By using a differential geometry that measures the phase difference of reflected or transmitted light from two adjacent points on a sample, it is possible to achieve a sensitivity of 0.35 A (or 0.75 X1 0-3 rad). Results of the surface studies on several samples are presented that clearly show the ability of the technique to image monomolecular layers and other minute surface perturbations.

The application of heterodyne and quasi-heterodyne (stepwise phase shifting) fringe interpolation techniques to contouring for 3-D object shape measurement is discussed. A setup with two spherical illumination sources for contour fringe generation is described. The contour fringe pattern can be observed in real time or from a holographic reconstruction. The use of a microcomputer for automated data acquisi-tion and processing allows one to determine the object shape for a large number of points and for arbitrarily shaped contour fringe surfaces. Experimental results are reported for both heterodyne and quasi-heterodyne phase measurement, offering a typical accuracy for object depth measurement of 0.2% of the lateral extension of the object.

Major advances in using coherent and incoherent speckle patterns for displacement and strain measurements are reviewed. Topics include the laws of spatial movement of laser speckle, the halo functions of coherent and incoherent speckle patterns, decorrelation factors and their effect on the fringe visibility and the upper limit of measurement, new techniques of holospeckle interferometry, real-time and electron microscopic speckle photographies, and the automatic processing of Young's fringes.

A novel technique, moire deflectometry, for ray deflection mapping is presented. Numerous experimental techniques for diagnostics of phase objects and specular surfaces, for shearing analysis, for microscopy, and for MTF determination, based on moire deflectometry, are described. The wide range of applications encompasses laser beam diagnostics, characterization of optical components, flow visualization in wind tunnels, temperature mapping of flames, turbulence study, and real-time tracking of transient phenomena like thermal lensing.

Structured light vision systems offer a practical solution to many 3-D inspection problems. This paper examines the trade-offs involved in the design of 3-D inspection systems that use triangulation. General equations describing the behavior of such systems are derived. The implementation of a multistripe system is discussed. Problems common among structured light systems are explored, and alternative solutions are suggested. Experimental results from a prototype system are presented.

In conventional triangulation systems for 3-D sensing there is a trade-off between range of depth and resolution. We propose a triangulation system with a large depth of field (1 m or more) and, at the same time, high resolution (20µm or better). The system is based essentially on a tele-axicon in the illumination device and on the use of the Scheimpflug condition in the observation device. A suitable scanning-by-deflection geometry is described.

Triangulation systems that are based on the simultaneous deflection of the illuminating and observing light beam are able to scan large object fields fast and with high space-bandwidth product. On the other hand, in nontelecentric systems, the direction of illumination and observation vary along the scan path, and the shape of an object is usually determined with respect to a circular reference shape. We describe a telecentric system with variable reference shape, stationary measuring geometry over the whole field, and expanded depth of field.

The growth of interest in spectral pattern recognition has been stimulated by the need to build instruments that respond to one object or type of object, possibly amid a host of other objects. The needed instruments include analyzers or alarms, medical diagnostic devices such as electroencephalogram or electrocardiogram analyzers, process control devices, and the like. The extra information provided by multivariate (spectral) data is always useful, if not essential, for such difficult tasks. However, the quantity of such data that can be provided by modern instruments requires that statistical pattern recognition techniques be used to extract the useful information from the noise.

A summary of the current status of spectral information on chemical agents, their spectral simulants, and possible field interferents is presented along with comments on current programs being used to expand this spectral data base. The current programs include the collection of Raman and near-infrared spectra and various methods of obtaining the real and imaginary refractive indices (primarily in the mid-infrared spectral region). All of the spectral information will be directly accessible to qualified users on the U.S. Army Chemical Research and Development Center's Univac computer.

This paper describes a chemical alarm system based on ion mobility spectrometry. The system consists of an ion mobility cell, a microprocessor, and an operator interface. The unit is designed to sound an alarm on specific chemical vapors. The microprocessor triggers the cell, collects and filters the signal, and implements a decision process based on linear discriminant functions. The paper describes the overall system and looks at the filtering and decision processes in detail.

A fundamental and widely used approach to feature selection is the method of linear discriminant analysis. The standard formulation of the analysis requires knowledge of the total and pooled within-class scatter matrices. Estimates of these matrices are made from training sets. In spectral pattern recognition, one is usually faced with large numbers of highly correlated measurements and only a small number of representative spectra. The training sets are typically inadequate, and the resultant estimates of pooled within-class scatter matrices are ill conditioned or singular. This precludes the use of the standard formulation of discriminant analysis. By formulating the discriminant analysis in terms of generalized singular value decompositions of total and pooled within-class deviation matrices, the method can be applied in situations where the scatter matrices are ill conditioned or singular. The approach is illustrated with an example two-class problem of distinguishing between Fourier transform infrared (FTIR) spectra of aliphatic hydrocarbons and alcohols.

A spatial filter spectral correlation method capable of distinguishing spectral absorption features due to a target trace gas from interfering absorption features of another gas has been developed. This technique was demonstrated for trace detection of gaseous formaldehyde in the 3.5 µm spectral region in the presence of large and variable amounts of interfering water vapor. The demonstrated success of this spectral correlator method will allow the routine detection and logging of formaldehyde levels of 10 to 100 ppb in indoor environments.