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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Sand Shear Band Thickness Measurements by Digital Imaging Techniques

Digital imaging analysis was used to study localized deformations in granular materials tested under plane strain condition. Two independent techniques were applied and compared. In the first, the digitized optical images of a grid printed on the latex membrane were used to measure the shear band orientation angle and thickness, and were found to be 54.5' and 3.01 mm respectively. The second technique involved introducing an ultra-low viscosity resin into the specimen in preparation for thin- sectioning and microscopic study of the internal fabric. A total of 24 microscopic images obtained from four thin sections were analyzed and void ratio variation was measured. The shear band thickness measurements from images located along the shear band axis (at two locations) were equal to 3.19 mm and 3.29 mm which are very close to the average value obtained from surface analysis. The study was then extended to investigate the effects of sand grain-size and properties, specimen density, and confining pressure on shear band thickness. It was found that the normalized shear band thickness decreases as grain-size and confining pressure increase and as density decreases. Finally, shear band thickness is highly influenced by the specimen dilatancy.

Alshibli, Khalid A.↗
NASA NTRS1992

Diversity imaging techniques in lidar

Diversity imaging techniques have been successfully employed in conventional microwave range-Doppler imaging radars to obtain high resolution images of both natural and man-made targets. These techniques allow microwave radars to achieve image resolution which would otherwise require excessively large antennas. Recent advances in coherent laser radar techniques and signal processing have led to the development of range-Doppler imaging laser radars. While much of the theory and signal processing techniques used in microwave radars can be brought to bear on laser radars, the significant difference in wavelength results in issues peculiar to laser radar systems. Both the fundamental concepts and specific applications of diversity imaging techniques applied to laser radar imaging systems will be discussed. Angle, frequency, and bistatic angle degrees of freedom can be employed in a coherent laser radar imaging system to achieve image resolution which exceeds the traditional Rayleigh criterion associated with the receive aperture. In diversity imaging, angle and frequency degrees of freedom can be used to synthesize an effective aperture providing range and Doppler target information. The ability to vary the bistatic angle provides an additional means of synthesizing an effective aperture. Both simulated and experimentally obtained laser radar images of spinning and/or tumbling objects utilizing both angular and frequency diversity will be presented. In coherent laser radar systems, image quality can be dominated by laser speckle effects. In particular, the signal-to-noise ratio (SNR) of a coherent laser radar image is at most unity in the presence of fully developed speckle. Diversity techniques can be utilized to improve the image SNR; simple incoherent averaging of images utilizing temporal and polarization degrees of freedom can significantly improve image SNR. Both the SNR and image resolution (as defined by the synthetic aperture) contribute to image quality. The relationship between the available degrees of freedom and image quality are discussed.

Schultz, K. I.↗
NASA NTRS2001

Analysis of High Contrast Imaging Techniques for Space Based Direct Planetary Imaging

We report on our ongoing investigations of a number of techniques for direct detection and imaging of Earth-like planets around nearby stellar sources. Herein, we give a quantitative analysis of these techniques and compare and contrast them via computer simulations. The techniques we will be reporting on are Bracewell Interferometry, Nisenson Apodized Square Aperture, and Coronagraphic masking techniques. We parameterize our results with respect to wavelength, aperture size, effects of mirror speckle, both mid- and high-spatial frequency, detector and photon noise as well pointing error. The recent numerous detections of Jupiter and Saturn like planets has driven a resurgence in research of space based high contrast imaging techniques for direct planetary imaging. Work is currently ongoing for concepts for NASA's Terrestrial Planet Finder mission and a number of study teams have been funded. The authors are members of one team.

Lyon, Richard G.↗
NASA NTRS1977

Signal-to-noise ratio analysis and evaluation of the Hadamard imaging technique

The signal-to-noise ratio performance of the Hadamard imaging technique is analyzed and an experimental evaluation of a laboratory Hadamard imager is presented. A comparison between the performances of Hadamard and conventional imaging techniques shows that the Hadamard technique is superior only when the imaging objective lens is required to have an effective F (focus) number of about 2 or slower.

Jobson, D. J.↗
NASA NTRS1982

Digital imaging techniques in experimental stress analysis

Digital imaging techniques are utilized as a measure of surface displacement components in laser speckle metrology. An image scanner which is interfaced to a computer records and stores in memory the laser speckle patterns of an object in a reference and deformed configuration. Subsets of the deformed images are numerically correlated with the references as a measure of surface displacements. Discrete values are determined around a closed contour for plane problems which then become input into a boundary integral equation method in order to calculate surface traction in the contour. Stresses are then calculated within this boundary. The solution procedure is illustrated by a numerical example of a case of uniform tension.

Peters, W. H.↗
NASA NTRS1991

Three dimensional scattering center imaging techniques

Two methods to image scattering centers in 3-D are presented. The first method uses 2-D images generated from Inverse Synthetic Aperture Radar (ISAR) measurements taken by two vertically offset antennas. This technique is shown to provide accurate 3-D imaging capability which can be added to an existing ISAR measurement system, requiring only the addition of a second antenna. The second technique uses target impulse responses generated from wideband radar measurements from three slightly different offset antennas. This technique is shown to identify the dominant scattering centers on a target in nearly real time. The number of measurements required to image a target using this technique is very small relative to traditional imaging techniques.

Younger, P. R.↗
NASA NTRS2018

Imaging Technique for High Precision Measurement of Detector Stability for the Ocean Color Instrument

One of the new projects by NASA to explore environmental change is the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) spacecraft. The primary instrument aboard the PACE spacecraft is the Ocean Color Instrument (OCI), an advanced optical spectrometer that will measure the color of the ocean from the ultraviolet to shortwave infrared range for the purpose of observing and monitoring ocean and coastal biology. As part of the optical alignment testing that must be completed before the instrument is built, the measurement stability of the detectors at space flight operating temperatures must be determined to ensure alignment is maintained. Therefore, this project focuses on the development of an imaging technique that adheres to testing requirements and can be used to determine the stability of the OCI detector. The movements of targets affixed to a high-precision stage were analyzed through an image processing program to test the ability of the imaging technique to detect very small (under 10 micrometers) movements. It was found that movements as small as half a pixel (~6 microns) and 1 pixel (~12 microns) were able to be accurately and consistently detected with this imaging technique. This project found that the designed image analysis technique fulfills testing and measurement requirements and will be an effective metrology technique for the OCI detector stability test.

Optics↗
NASA NTRS2009

Development of Backscatter X-Ray Imaging Techniques for Space Vehicle Applications

This slide presentation reviews the development of backscatter x ray (BSX) imaging techniques to perform inspection of spacecraft components. The techniques are currently being enhanced to advance Non-Destructive Testing (NDT) methods for future space vehicle applications. The presentation includes an overview of x ray techniques, a description of current BSX applications used on the space shuttle, the development for Constellation applications, and the use of the system for foam applications.

Bartha, Bence B.↗
NASA NTRS1977

Lunar surface chemistry - A new imaging technique

Detailed chemical maps of the lunar surface have been constructed by applying a new weighted-filter imaging technique to Apollo 15 and Apollo 16 X-ray fluorescence data. The data quality improvement is amply demonstrated by (1) modes in the frequency distribution, representing highland and mare soil suites, which are not evident before data filtering, and (2) numerous examples of chemical variations which are correlated with small-scale (about 15 kilometer) lunar topographic features.

Andre, C. G.↗
NASA NTRS1976

Geometric assessment of image quality using digital image registration techniques

Image registration techniques were developed to perform a geometric quality assessment of multispectral and multitemporal image pairs. Based upon LANDSAT tapes, accuracies to a small fraction of a pixel were demonstrated. Because it is insensitive to the choice of registration areas, the technique is well suited to performance in an automatic system. It may be implemented at megapixel-per-second rates using a commercial minicomputer in combination with a special purpose digital preprocessor.

Tisdale, G. E.↗
NASA NTRS1993

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique

A new oil-fringe imaging fkin friction (FISF) technique to measure skin friction on wind tunnel models is presented. In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced proportional to local skin friction. After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer. Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions.

Monson, Daryl J.↗
NASA NTRS1993

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique

A new oil-fringe imaging system skin friction (FISF) technique to measure skin friction on wind tunnel models is presented. In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced in proportion to local skin friction. After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer. Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions.

Monson, Daryl J.↗
NASA NTRS1996

Application of magnetospheric imaging techniques to global substorm dynamics

The application of remote sensing techniques to the analysis of the dynamics of storms and substorm processes is discussed. The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission, its mission and instruments are presented. The following are discussed: neutral atom imaging; radio plasma techniques; photon imaging, and substorm observations.

Green, James L.↗
NASA NTRS1990

A Planar-Fluorescence Imaging Technique for Studying Droplet-Turbulence Interactions in Vaporizing Sprays

Droplet turbulence interactions directly affect the vaporization and dispersion of droplets in liquid sprays and therefore play a major role in fuel oxidizer mixing in liquid fueled combustion systems. Proper characterization of droplet turbulence interactions in vaporizing sprays require measurement of droplet size velocity and size temperature correlations. A planar, fluorescence imaging technique is described which is being developed for simultaneously measuring the size, velocity, and temperature of individual droplets in vaporizing sprays. Preliminary droplet size velocity correlation measurements made with this technique are presented. These measurements are also compared to and show very good agreement with measurements made in the same spray using a phase Doppler particle analyzer.

Santavicca, Dom A.↗
NASA NTRS1989

Psychophysical rating of image compression techniques

Image compression schemes abound with little work which compares their bit-rate performance based on subjective fidelity measures. Statistical measures of image fidelity, such as squared error measures, do not necessarily correspond to subjective measures of image fidelity. Most previous comparisons of compression techniques have been based on these statistical measures. A psychophysical method has been used to estimate, for a number of compression techniques, a threshold bit-rate yielding a criterion level of performance in discriminating original and compressed images. The compression techniques studied include block truncation, Laplacian pyramid, block discrete cosine transform, with and without a human visual system scaling, and cortex transform coders.

Stein, Charles S.↗
NASA NTRS1974

New theoretical models and ratio imaging techniques associated with the NASA earth resources spectral information system

Four independent investigations are reported; in general these are concerned with improving and utilizing the correlation between the physical properties of natural materials as evidenced in laboratory spectra and spectral data collected by multispectral scanners. In one investigation, two theoretical models were devised that permit the calculation of spectral emittance spectra for rock and mineral surfaces of various particle sizes. The simpler of the two models can be used to qualitatively predict the effect of texture on the spectral emittance of rocks and minerals; it is also potentially useful as an aid in predicting the identification of natural atmospheric aerosol constituents. The second investigation determined, via an infrared ratio imaging technique, the best pair of infrared filters for silicate rock-type discrimination. In a third investigation, laboratory spectra of natural materials were compressed into 11-digit ratio codes for use in feature selection, in searches for false alarm candidates, and eventually for use as training sets in completely automatic data processors. In the fourth investigation, general outlines of a ratio preprocessor and an automatic recognition map processor are developed for on-board data processing in the space shuttle era.

Vincent, R. K.↗
NASA NTRS1973

Imaging techniques in X-ray astronomy.

Some of the imaging problems encountered in space-borne X-ray astronomy are reviewed, along with the techniques considered for their solution. Following a discussion of X-ray focussing and X-ray image processing, the development of X-ray imaging devices is surveyed. It is shown that the imaging devices that will be used in X-ray astronomy will take advantage of developments intended for infrared and optical astronomy. The special requirements of X-ray observation - especially, single photon detection and high time resolution - rule out the use of existing devices, particularly because of readout problems.

Gursky, H.↗
NASA NTRS1973

Developments in electronic imaging techniques; Proceedings of the Seminar-in-Depth, San Mateo, Calif., October 16, 17, 1972.

Capabilities and limitations of infrared imaging systems are discussed, and a real-time simulator for image data systems is described. Ultrahigh resolution electronic imaging and storage with the return beam vidicon is treated, and a description is given of an electron-lens for opaque photocathodes. Ground surveillance with an active low light level TV, digital processing of Mariner 9 TV data, image enhancement by holography, and application of data compression techniques to spacecraft imaging systems are given attention. Individual items are announced in this issue.

Zirkind, R.↗