Report on Astronomy III Seminar My column this month is a review of the seminar on Astronomy III in Tucson, Arizona, 29 January through 1 February 1979. Six sessions focused on the latest instruments and techniques for visible, infrared, and ultraviolet astronomical observations and details of data reduction and image enhancement necessitated by these new techniques, I was surprised by the breadth of peripheral subjects with which today's astronomer must be familiar. Computer techniques and programming, instrument design, imaging tubes, infrared and ultraviolet detectors, image extraction and enhancement, cooled optics, and space technology were some of the topics covered.
Optical activities in the Huntsville area have been driven primarily by government and industrial requirements. These requirements were formulated largely by the Army, R&D work at Redstone Arsenal. They were expanded with the establishment of NASA's Marshall Space Flight Center in the early 1960s. Local optical activity expanded rapidly, in step with the space program. By 1969, the optical community in Huntsville formed a significant part of the available technical resources. This fact was formalized on October 20, 1969, when the Optical Society of America voted to recognize the Huntsville section of OSA. The first section president was Charles L. Wyman. The organization was large and active from the beginning. Within a few months of recognition, there were 175 individual members, many working in advanced areas of optical research and development, and nine corporate members. Within six months of recognition, the section was holding an all-day symposium. Recently this organization joined with SPIE to form the Electro-Optical Section and Working Group in Huntsville.
A particle sizing instrument has been developed as part of a research program in particle sizing interferometry conducted by the Arnold Engineering Development Center. The instrument, which uses fringe visibility to size particles, has been applied to determination of water droplet size distributions in a wind tunnel employed for icing studies. Droplets were sized in the range from 8 to 80 micrometers, while droplet velocities in the air flow were in excess of 100 meters/second. Number densities ranged up to a few hundred droplets per cubic centimeter. Design features of the system are described, including on-axis, forward scatter light collection optics which use a specialized lens mask to reduce the dynamic range of signal magnitudes. The variation of the sample volume with particle size is discussed. The electronics are outlined and signals are described in both the time and frequency domains.
The Holographic Optical Schlieren System (HOSS) is a prototype optical instrument which provides an interim holographic recording of the output wavefront from a classical type schlieren-shadowgraph system. This interim holographic recording may be used to reconstruct the wavefront for schlieren, shadowgraph, interferometric and other analyses techniques at the convenience of the experimenter. A description of the optical system along with an assessment of its capabilities and performance is provided.
This paper will review briefly the requirements of holography with respect to particle sizing techniques. A holographic construction system and the appropriate reconstruction system will be discussed regarding their characteristics and performance (i.e. system resolution, magnification, system aberration and correction of aberrations, and maximum total test volume). The capabilities of a commercial particle sizing system used to obtain particle sizes and distribution information from reconstructed holograms will be described and characterized. It will be shown that by using the methods described, high resolution throughout large test volumes can be achieved.
In-line and sideband holography have been applied to the analysis of particles and liquid droplets in air flows at the Arnold Engineering Development Center. The optical systems of the holocameras, the quality of the reconstructed data, and the effects of field parameters on image quality are discussed.
A coherent optical correlation technique is used to measure surface displacements. In the event that the surface roughness of the test object is invariant during the object's translation, the correlation intensity peak remains constant. A simple relationship between the displacement of the surface and the displacement of the peak correlation signal is found and experimentally verified.
The National Aeronautics and Space Administration is developing a 2.4 meter aperture astronomical telescope, the Space Telescope, to be placed in earth orbit in the early 1980s. Free of the earth's atmosphere, this international observatory will provide astronomers with an electromagnetic window from the far ultraviolet to the near infrared. Moreover, the Space Telescope is being designed to provide near-diffraction limited imagery at visible and longer wavelengths which will provide angular resolution that surpasses the largest of ground based observatories. This paper reviews the optical technology that has been developed over the last decade to bring the Space Telescope to a practical reality. The optical design of the telescope, the optical performance control system, and the anticipated orbital performance is presented as well. In addition, the initial complement of focal plane instruments, being developed concurrently, is described.
The near-zero gravity environment of Spacelab presents the opportunity to perform many new fluids experiments which cannot be done in earth-bound laboratories. A large number of these investigations involve relatively small and confined volumes of fluid. Hence, fluid measurement techniques are required which do not disturb the flow. Several nonintrusive measurement techniques are being investigated. A photochromic dye method is being developed for flow measurement. Photochromic dyes are substances which darken upon exposure to ultraviolet (UV) radiation and then clear up again spontaneously. A small amount of dye (~.025% by weight) has been successfully dissolved in a low viscosity silicone oil and dye streaks created upon exposure to an UV source. The movement of the streaks reveals the flow. The streaks then clear up so that the procedure can be continued without the liquid becoming opaque. A laser Doppler dual-scatter system is also being developed for low flow speed measurement. An accuracy of a few percent has been demonstrated for flows of a few millimeters per sec. A double grid schlieren system is being developed for temperature measurement. The optical arrangement is such that an image of a Ronchi ruling is superposed on the original ruling giving a uniform grey field of view. Departures from the background are caused by light being refracted as it passes through the experimental volume.
The Solar Maximum Mission experiment contingency will include one instrument originally designed and built for OSO-8. The engineering model of the OSO-8 High Resolution Spectrometer has been rebuilt to make it flightworthy and to encompass several new functions, including solar ultraviolet polarimetry. The rebuilt package is designated as the High Resolution Ultraviolet Spectrometer/Polarimeter. The device that enables polarimetry is a dual channel rotating waveplate system. The waveplates are magnesium fluoride and will allow measurements to be made ranging from the Lyman Alpha line to near visible ultraviolet. One waveplate channel will use the polarization characteristics of the spectrometer diffraction grating as the analyzer. The second channel has a built-in four-mirror polarizer. This paper describes the polarimeter design, operation, and calibration.
Low-light-level television systems have been utilized to gain information on meteors, aurorae, and other faint, transient astronomical phenomena. Such phenomena change not only their position as a function of time, but also their photometric and spectral characteristics in as little as 1/60 second, thus requiring unique methods of analysis. Data observed with television systems and recorded on video tape have been analyzed with a system utilizing both analog and digital techniques. Both off-the-shelf equipment and inhouse developments are used to isolate sequences of moving images and to store them in a form suitable for photometric and spectral reduction. Current emphasis of the analysis effort is directed at the measurement of the first-order emission lines of meteor spectra, the results of which will yield important compositional information concerning the nature of the impinging meteoroid.
An Automated Laser Seeker Performance Evaluation System (ALSPES) has been developed at the US Army Missile Research and Development Command (USAMIRADCOM) which utilizes a minicomputer to implement the control functions required to test electro-optical (E /0) guidance systems. Software programs have been written for a series of tests which fully evaluate E /0 seeker performance. Test conditions are fed into a CRT terminal and the minicomputer conducts a fully automated, "hands-off" test by varying such parameters as laser energy, target position and velocity, seeker position and angular rate, and time separation between targets. This paper discusses the types of automated tests performed, the electro-optical test equipment utilized and the layout of the test facility, the minicomputer to test equipment interface, and the cost savings resulting from the development of this automated test facility.
A crucial experiment, relative to determining the ability of an imaging seeker to track a target and generate accurate terminal guidance, requires an optical device which can provide imagery that grows in size as a real-time estimate of true missile flight conditions. The basic components of an Optical Contrast TV Imaging Seeker are reviewed to establish the need for an optical target simulator. An optomechanical device called a Variable Optical Target Simulator (VOTS) which generates end game scene situations is discussed. The organization of optical components and their control for providing an image which grows in size as a linear estimate of real world situations is presented.
Signal processing in scanning sensors is dominated by two processing requirements: signal detection/peak extraction and multi-frame correlation. Techniques for the detection of target pulses and extraction of their peaks are outlined and compared in this paper. Pulse detection techniques discussed include matched filters, least-square filters, partial wave filtering, nonlinear filters, and pattern recognition. The problem of peak extraction in unresolved pulses is also discussed. Multiframe correlation techniques discussed include two-dimensional windowing, multi-dimensional windowing, polynominal tracking, vector correlation, and moment matching.
By applying nonlinear modeling to multiband radiometric data, one can mathematically extract radiation characteristics of certain classes of optically unresolvable sources. This paper considers sources whose signatures are composed of blackbody, graybody, and known non-Planckian radiation. Algorithm sensitivity in the presence of white noise has been investigated using Monte Carlo techniques and is also presented. The paper also develops the theoretical basis and implementation of the method and demonstrates the ability of the algorithm to determine the number of graybodies in an unresolved source.
To evaluate an optical sensor's performance capabilities for specific system applications, it is often cost effective to simulate the optical component's response to the intended environment and the subsequent effect on the system's performance. High-fidelity computer simulations have been developed which provide valuable assistance to hardware development programs. The elements and techniques of optical system simulations are described, accompanied by samples of results. Existing high-fidelity simulations are described and computational resources discussed.
A method for simultaneously observing monochromatic images from a polychromatic source is presented that utilizes an imaging selective modulation interferometric spectrometer. With this technique, rapidly varying changes in many spectral components may be simultaneously monitored. After a brief review of the theory (mostly qualitative), the modifications and techniques necessary for producing more than one spectral image will be discussed.
Two-mirror grazing incidence telescopes with one conical mirror surface were designed and analyzed and compared to the classical Wolter-type configuration. Even though performance improvements could not be expected, the simplicity of these systems is attractive. An additional advantage is that the grazing angle along a surface varies much more slowly in systems with one conical surface, rendering, for a given range of grazing angles, a significantly larger collecting area.
A system was fabricated to demonstrate the utility of noncontact electro-optical switching to the testing of electronic circuit boards at the component level. This paper summarizes the results of tests on inventory avionics circuit boards and reviews the underlying concepts for the new noncontact probing technique.
The design and performance of a CO2 CNN' Electric Discharge Laser (EDL) is described. Particular emphasis is given to the effects of medium inhomogeneities and mode medium interaction on the properties of the output beam. Experimental results show medium density profiles, predominantly linear, quadratic and cubic, arising from the heating due to power loading of the gas. Fluctuations in the output flux are also shown. These arise from the interaction of the mode flux with the medium. The variation of this interaction with device parameters on beam quality is discussed. Experimental results showing a minimal impact of mode-medium effects on beam quality are shown.
A dust-trajectory technique for flow velocity measurement in a compressible medium is discussed. The technique consists of suspending zinc stearate powder in the compressible medium. The dust particle is illuminated by an intense light flashed at a desired frequency. The dust trajectory is photographed and analyzed to determine the flow velocity. Three sample tests were used to demonstrate the utility of the technique. Errors of the method were also analyzed that show the dust trajectory being truly representative to the fluid motion. Errors are resulted primarily from the measurement of length and rpm which could be analyzed in a traditional fashion. The method is particularly suited for flow measurements in small spaces in which most present techniques are handicapped. Given the available light source and film speed, the method works best in the medium velocity range.
This paper is concerned with the properties of the rising-sun frequency-modulation reticle as it affects the generation of error-signal problems. The exact relations between the errors and the target position are given.
The parallelism of optically parallel plates is generally measured by interferometers, autocollimators or dial gauges, depending on the accuracy required. A simple method is devised to measure the parallelism of opaque optical components, such as germanium windows, for which the conventional techniques of interferometric measurement in visible light could not be used conveniently.
With a dual channel control system, experiments have been conducted to demonstrate the ability to control the relative frequencies and phases among an array of lasers to a high degree of accuracy in a noisy environment. Both piezoelectric and intracavity electrooptic length control were used in the processing system. Success of this implementation demonstrates the feasibility of using laser arrays to produce optical waveforms of arbitrary specification.