After nearly twenty years in the field of applied diagnostic holography I have become thoroughly weary of seeing holography "written off" because the data reduction is "too time-consuming and cumbersome." Too often, this description of holography has been made without putting the technique in proper perspective. One main reason for holographic data being difficult to process is that the quantity of data that can be (and usually is) stored in a hologram is staggering. This should be touted as an advantage, not a disadvantage. The other major reason for the difficulty of processing holographic data is that holograms also store a staggering amount of noise that too often has an appearance similar to the data. Coherent noise does not just add, it adds coherently, thereby amplifying its effect on the resulting data.

A system for digital interferogram evaluation based on an image-processing system connected to a host computer has been implemented. The system supports one- and two-dimensional interferogram evaluations. Interferograms are digitized, enhanced, and segmented. The fringe coordinates are extracted, and the fringes are represented as polygon data structures. Fringe numbering and fringe interpolation modules are implemented. The system supports editing and interactive features as well as graphic visualization. An application of the system to the evaluation of double exposure interferograms from the transonic flow field around a helicopter blade and the reconstruction of the 3-D flow field are aiven.

A new algebraic reconstruction technique code based on the iterative refinement method of least squares solution for tomographic reconstruction is presented. Accuracy and the convergence of the technique were evaluated through the application of numerically generated interferometric data. It was found that, in general, the accuracy of the results was superior to other reported techniques. The iterative method unconditionally converged to a solution for which the residual was minimum. The effects of increased input data error, limited total viewing angle, and reduced number of input data were studied. The inversion error was found to be a function of the input data error only. The convergence rate, on the other hand, was affected by all three parameters. Finally, the technique was applied to experimental data, and the results are reported.

Computer graphics and theoretical descriptions of density are used to obtain computer-genirated flow visualizations called computational interferograms. Computational interferograms are pictorially analogous to optical interferograms, and examples showing the fringe pattern for the flow about a sharp-tip cone in a supersonic air stream are presented. To ascertain the effect of unsteady behavior, local density disturbances are added to the steady-state flow field. This introduces into the computational interferogram irregularities like those seen in optical interferograms. These theoretical disturbances can be varied in geometry and density description, translated with time, and strength-ened or dissipated. The accuracy of computational interferometry relies on the accuracy of the theoretical density description and, therefore, provides a way of verifying existing models of flow fields, especially those containing unsteady or turbulent behavior. In addition to being a unique method of flow visualization, computational interferometry can be used to develop and modify theories or numerical solutions to both simple and complex flow fields. The present research is a general description of this process.

This paper examines the aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers. The data present comparisons of observed optical performances with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microseconds temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite-aperture, time-averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q-switched Nd:YAG double-pulsed laser and a holographic camera that recorded the random flow field in a double-pass, double-pulse mode. Aero-dynamic parameters were measured using hot film anemometer probes and a five-hole pressure probe. Each technique is described with its associated theo-retical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered. The results presented represent five flights flown at altitudes from 1.8 km to 10.7 km and at Mach numbers from 0.32 to 0.79. Single-pass phase deviations for the boundary layer were from 0.06 to 0.17 waves (at X = 0.53 ;Am) with piston and tilt components removed. Measured phase deviations for the artificially induced shear flows were from 0.10 to 0.279 waves (at X = 0.53 /um) with piston and tilt components removed. However, when low order aberrations through coma were removed, the remaining deviations were only 0.09 to 0.18 waves. This resulted in a 33 to 250% increase in the Strehl ratio at the 14 cm optical aperture. It was further shown that the low order aberrations corresponded to the longer wavelengths in the random flow, and these waves propagated with a longer characteristic time than the higher order aberrations (200 to 1000 /As versus 50 to 100

Optical interferometry techniques have been applied to the investiga-tion of transonic airfoil flow fields in large-scale wind tunnels. Holographic interferometry techniques were used in the study of two-dimensional sym-metric NACA 64A010 and Douglas Aircraft Company DSMA671 supercritical airfoil performance in the NASA Ames 2 ft X2 ft transonic wind tunnel. Quan-titative data obtained from the interferograms were compared to the surface pressure data. The excellent agreement obtained verified the accuracy of the flow visualization and demonstrated the potential for acquiring quantitative scalar results. Measurements of the inviscid flow speed and the boundary layer and wake velocity profiles were extracted from the interferograms and com-pared to laser Doppler velocimeter measurements. These results were also in good agreement. A method for acquiring real-time interferometric data in large-scale facilities was developed. This method, based on the point diffraction interferometer, was successfully tested in the Ames 2 ft X2 ft transonic wind tunnel. The holographic and real-time interferometry methods were applied to the investigations of circulation control airfoils utilizing the Coanda effect. These results revealed the details of the jet interaction with the trailing edge boundary layer and the other parameters affecting the lift augmentation.

A preliminary study of approaches for extracting and analyzing data from particle holograms concludes that (1 ) for "thin" spherical particles, out-of-focus methods are optimum; (2) for "thin" nonspherical particles, out-of-focus methods are useful but must be supplemented by in-focus methods; and (3) a complex method of projection and back-projection can remove the unwanted out-of-focus data for "deep" particles.

The General Motors Research Laboratories has developed an image processing system that automatically analyzes the size distributions in fuel spray video images. Images are generated by using pulsed laser light to freeze droplet motion in the spray sample volume under study. This coherent illumina-tion source produces images that contain droplet diffraction patterns representing the droplet's degree of focus. Thousands of images are recorded per sample volume to get an ensemble average of the distribution at that spray location. After image acquisition the recorded video frames are replayed and analyzed under computer control. The analysis is performed by extracting feature data describing droplet diffraction patterns in the images. This allows the system to select droplets from image anomalies and measure only those droplets con-sidered in focus. The system was designed to analyze sprays from a variety of environments. Currently these are an ambient spray chamber, a high pressure, high temperature spray facility, and a running engine. Unique features of the system are the totally automated analysis and droplet feature measurement from the gray scale image. Also, it can distinguish nonspherical anomalies from droplets, which allows sizing of droplets near the spray nozzle. This paper describes the feature extraction and image restoration algorithms used in the system. Preliminary performance data are also given for two experiments. One experiment gives a comparison between manual and automatic measurements of a synthesized distribution. The second experiment compares measurements of a real spray distribution using current methods and using the automatic system.

The size distribution of a particle field hologram is obtained with a Fourier transformation of the Fraunhofer diffraction pattern of the reconstructed hologram. Off-axis absorption holograms of particle fields with known characteristics were obtained and analyzed with a commercially available instrument. The mean particle size of the reconstructed hologram was mea-sured with an error of ±5%, while the distribution broadening was estimated within ±15%. Small sections of a pulsed laser hologram of a synthetic fuel spray were analyzed with this method, thus yielding a spatially resolved size distribution. The method yields fast and accurate automated analysis of particle field holograms.

An automated data reduction system for the analysis of interference fringe patterns obtained using the particle image velocimetry technique is described. This system is based on digital image processing techniques that have provided the flexibility and speed needed to obtain more complete automation of the data reduction process. As approached here, this process includes scanning/searching for data on the photographic record, recognition of fringe patterns of sufficient quality, and, finally, analysis of these fringes to determine a local measure of the velocity magnitude and direction. The fringe analysis as well as the fringe image recognition are based on full-frame autocorrelation techniques using parallel processing capabilities.

A "portable" holographic microscope with a nanosecond Q-switched ruby laser illuminator has been assembled. The system has been used to record dust phenomena under field test conditions.

Expressions are derived in closed form for the optical signatures resulting from test alignment and from several controllable machining parameters, to lowest order, in the manufacture of diamond-turned mirrors of the type comprising conic sections of revolution. Transformation of these effects to the local coordinate systems of off-axis sections of these optics yields converging series of Seidel wavefront aberrations. This information can be used to distinguish artifacts stemming from alignment of the optic from those arising from such parameters as tool offset and local tool path adjustments. It is also shown how, by allowing a departure of the optic axis from the machining axis, these effects can be used to control an aberration of choice (e.g., clover) that departs from that class having variation only transverse to the trace of the tool across the local aperture.

A saddle mirror has opposite curvatures in the two principal sections. Such an optical element has some very interesting properties, the important one being that it gives a nonreversed image for an object located in front of and some distance away from it. However, once such a mirror is made, it is difficult to vary the two powers in the two principal sections to enable one to change the size of the image. This paper considers the possibility of combining two separate cylindrical surfaces, in the form of a lens and a mirror, that can be rotated to change the effective curvatures in the principal sections of the equivalent saddle mirror. Several methods for achieving this type of system are described.

The mastering of an industrial process to economically manufacture high precision aspherics is of utmost importance to obtain high performance infrared systems in the 3 to 5 and 10 to 13 i2m ranges. The research and the results of such a process are presented. Starting with a spherical surface very close to the desired profile, material is deposited by vacuum evaporation. Between the rotating lens and the source, one or several masks of specific shapes determines the aspherical curvature profile. Up to 50 um of material can thus be added to a sphere, with a precision of 0.1 µm.

Accurate and reliable detection of unique objects is an important component of an image understanding system. The objects are considered to have a unique pattern and should be recognized based upon their own characteristics. An object detection approach applicable to high resolution aerial images is developed in the paper. The methodologies incorporate features such as minimal sensitivity to the backgrounds on which objects may appear, ability to detect objects appearing in arbitrary orientations, and use of a unified set of operators to analyze various levels of details. Specifically, the gray-level co-occurrence matrix is used to provide the early vision operators. Results of several experiments show promise for the proposed methods. The methods can constitute an important part of an object identification system in which use of such properties as object size, shape, reflectance, etc., is possible.

A new technique has been developed for geometrically rectifying images to subpixel accuracy in real time through high fidelity resampling. This technique permits significant simplification and cost reduction for a remote sensing system by relaxing the optical/mechanical alignment tolerances by about two orders of magnitude. A pipelined resampling processor has been built whose small size, weight, and power consumption permit it to be used on board a spacecraft or other vehicle. The high throughput of the processor prevents data logjams and permits the use of resampling kernels with better MTF and phase linearity than previously practical. A new design criterion that produces improved uniformity of MTF in the final image has been identified for the resampling kernels. These improvements over conventional resampling techniques result in improved data quality delivered to the end user and offer opportunities for streamlined data distribution. This technique and processor can also be applied to image motion compensation, data set merging, man-in-the-loop image warping, and image motion generation.

For attainment of near-intrinsic losses in the 2 to 4 µm range, concentrations of cations such as iron, cobalt, nickel, and copper must lie in the 0.2 to 10 ppb range (1 ppb = 1 mol/109 mol of glass). Commercial grades of zirconium salts tend to form colloids and to contain hundreds or thousands of times more than the tolerable concentrations. We have found filtration to be partially effective for colloid removal. Working with relatively concentrated (2 molar, about 17% by weight) solutions of Zr salts, we have introduced about 7000 ppb each of Fe, Co, Ni, and Cu. We have determined that all of these metals can readily be removed by laboratory-scale ion-exchange methods to meet the cation-purity standards for near-intrinsic absorption.

A phase contrast heterodyne interference optical microscope for the precise characterization of optical path distribution across a transversely illuminated single or multi mode fiber is described. Using the Abel inversion algorithm in conjunction with this measurement, an exact profile of the refractive index can be extracted. The fiber is immersed in an index-matching liquid to ensure small optical path phase variation. This scheme is valid for any refractive index profile, assuming the fiber is cylindrically symmetric and its index of refraction is a function of the radial distance only. The technique is attractive since it requires minimum fiber preparation and has the potential of on-line index monitoring without breaking into the fiber. A brief theoretical analysis is given to illustrate the feasibility and potential of the proposed method.

Heavy metal fluoride glasses (HMFG) are potentially useful as optical components in a wide range of devices. Their utilization has so far been delayed mainly because of insufficient material purity and inadequate processing conditions. However, as the result of numerous research efforts, these problems are gradually diminishing, and it now seems likely that the ultimate limitations for use of HMFG components, at least in those applications in which high optical transparency is not a prerequisite, will be imposed by more intrinsic instabilities of the glasses themselves. These include their strong tendency to crystallize on quenching and subsequent reheating, low mechanical and chemical durability, and the possibility that they will undergo significant physical aging in situ. Experimental data relating to these problems have now been obtained, and their relative importance is assessed in this paper.

Recent investigations in digital tomography modalities utilizing conventional tomographic x-ray equipment have required the use of image intensifier (11)/TV imaging systems. The retrofitting of these systems presented certain geometric problems, one of which was the discrepancy between the mechani-cal fulcrum position and the true anatomical cutting plane due to the rigid mounting of the 11/TV system to the conventional film cassette Bucky. An electronic module was designed that corrects for this discrepancy, affords automatic fulcrum height programming features, and displays the correct position. The module is suitable to many similar applications with some minor modification.

Infrared background data are usually presented in the form of time histories and various statistics. The statistics in the time domain include means, variances, a utocorrelations, and histograms of various types. The statistic usually presented in the frequency domain is power spectral density. The data in either the time or the frequency domain may be useful, depending on how the system designer chooses to implement his filtering system and perform his system calculation. This paper examines the requirement for consistency in the two domains and shows how well certain windowing techniques assure con-sistency between the time and frequency domains. A particular technique is shown to give virtually perfect consistency. Data from the Balloon Altitude Mosaic Measurement (BAMM) are used to illustrate the results.

We have studied the performances of Mangin mirrors and simple spherical mirrors for optical processing with feedback by using the mirrors in a confocal Fabry-Perot system. It has been found that the mirror sets behave experimentally as predicted theoretically; i.e., both the space-bandwidth product and the imaging characteristics of the confocal Fabry-Perot system obtained by using Mangin mirrors are better than those obtained by using simple spherical mirrors. Taking advantage of these improvements, the optical processor with feedback will be able to process more information in parallel with greater accuracy.

A discussion is presented of a modification to the molecular absorption band models in the LOWTRAN code for the uniformly mixed (N 20, CH4, CO, 02, and CO2) and the trace (NO, NO2, NH3, and SO2) gases. The transmission function adopted for each model consists of a double exponential defined by three absorber parameters and a single spectral parameter. All the parameters were determined optimally through a numerical procedure that incorporates line-by-line and measured transmittance spectra. Vertical concentration profiles are provided for these gases that may be used together with the 33-levels standard atmospheres in the calculation of slant-path transmittances. The present single model for the uniformly mixed gases in LOWTRAN is compared with the combination of the proposed individual models.

In order to accomplish scientific objectives, the ultraviolet spec-trometer and polarimeter (UVSP) for the Solar Maximum Mission incorporated into its design a rotatable, multiple-slit aperture plate assembly that contained 15 beam splitters and 10 deflectors. The beam splitters were extremely small, sharp-edged mirrors that were required to split spectral lines (1100 to 3200 A) at their centers with minimum light loss and scattering. Processes were devel-oped to fabricate and accurately mount these miniature prism-shaped mirrors, whose greatest dimension in all cases was less than 3 mm and whose leading edges, which were required to be sharper than 2 Am, were actually as small as 0.3 Am. Other optical components of the UVSP, while not as unique as the beam splitters, demanded unusual precision in their fabrication because of the complexity and resolution of the instrument. These were the telescope primary and secondary mirrors and metering rods for maintaining a precise distance between them, a spherical Ebert mirror, a holographically ruled diffraction grating with an antireflection coating under the photoresist to suppress unwanted secondary reflections, and a four-element UV polarizer.

To John Conant for six hard years of behind-the-scenes work, and To his staff (Barbara DeNapoli, Ann Lear, Ruth Azevedo, and Irene (Breen) for supporting him; To two successive managing editors (Marybeth Manning and Eric Pepper), who maintained the high standards of quality set by their predecessor, Elaine Cherry, Director of Publications 'for the Society; To my predecessor, John DeVelis, for continued encouragement; To my friend, Joe 'aver, Executive Director of SPIE, for his unfailing support; To Aerodyne Research, Inc., and especially to Chuck Kolb and Jim Draper, for six years of support not necessarily visible to anyone but me; To Joe Horner and Winn Gaynor for making "SPIE Reports" exciting and valuable; To the best executive secretary I have ever known, Shirley Fedukowski, for trying so valiantly to keep me organized; To the many contributors, special issue editors, reviewers, and readers of Optical Engineering-Thank you. I have truly appreciated your help.

A recurring problem common to most IR systems operating in a closed area is the presence of interfering background events that degrade their detection capabilities. This article deals with the effects various light sources may have on the reliable operation of IR-based instruments and systems in indoor applications.