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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Optical computing with laser light

Linear and nonlinear optical processing techniques (Fourier transformation, convolution and correlation, arithmetic operations - addition and subtraction with gratings, generalized orthogonal transformations; theta modulation, half-tone screen process, optical feedback) for mathematical computations are reviewed. The use of gratings and computer holograms in addition, subtraction, differentiation, and application of generalized transformations is discussed. Use of nonlinear optical elements with or without optical coherent feedback in such nonlinear operations as taking logarithms and thresholding is described. Applications in hybrid systems incorporating digital computer and optical processor with real-time interface devices, or optical threshold and logic devices for parallel processing to apply digital techniques to optical information are considered.

Lee, S. H.↗
NASA NTRS1977

Plasma field characteristics of directional discontinuities in the interplanetary medium

The paper examines plasma and magnetic-field changes occurring across 1359 directional discontinuities taken from interplanetary data spanning almost four solar rotations. The plasma field characteristics of these events exhibit a distinct variation with large-scale solar-wind velocity. At low velocities, tangential discontinuities appear to predominate. At higher velocities, a substantial and increasing fraction of directional discontinuities exhibits the plasma field properties expected of outwardly propagating rotational discontinuities. The results of Sari (1972, 1975) and of the present study suggest that in the calculation of propagation diffusion coefficients for low-energy cosmic rays, the effects of directional discontinuities should be subtracted from the magnetic fluctuation spectrum during relatively quiet wind conditions. It is not clear that such subtraction is necessary during more disturbed periods.

Solodyna, C. V.↗
NASA NTRS1976

Shockless airfoils with thicknesses of 20.6 and 20.7 percent chord analytically designed for a Mach number of 0.68 and a lift coefficient of 0.40

A 20.8 percent-thick airfoil shape was designed to have shockless inviscid flow at a Mach number of 0.68 and a lift coefficient of 0.40. In order to determine the actual airfoils which would yield this same shockless flow when viscous effects are included, boundary layer displacement thicknesses were subtracted from the inviscid shape for Reynolds numbers of 100 and 35 million. This process yielded airfoils with thicknesses of 20.7 and 20.6 percent, respectively. Subtraction of boundary layer displacement thicknesses for Reynolds numbers below 35 million yielded nonphysical airfoils, that is airfoils with negative thicknesses near tHe trailing edge. The pitching moment about the quarter-chord point at the design condition was -0.082 for the inviscid shape and, consequently, for both airfoils. Off-design calculations for the two airfoils were made using a computer program which provides for the interaction of the inviscid flow and boundary layer solutions. The pressure distributions of the airfoils were shockless for conditions from the design point to lower Mach numbers and lift coefficients. No boundary layer separation was predicted except in the last 3 percent chord on the upper surface.

Allison, D. O.↗
NASA NTRS1978

Cloud type separation by spectral differencing of image pairs

A technique is presented for discriminating different cloud types through an image subtraction of visible and infrared SMS/GOES picture pairs. The technique emphasizes how one could separate snow from clouds and identify cirrus by the subtraction method. Quantitative threshold values are shown which can be used in an objective manner to make this separation. Use is made of an all-digital image display device allowing such mathematical operations to be performed on satellite data. Techniques such as this can be made operational through the interfacing of the image analysis system with a direct-readout SMS/GOES ground station and distribution network.

Reynolds, D. W.↗
NASA NTRS1978

'Smart', remote holographic processor based on the materials characteristics of LiNbO3

A class of 'Smart' remote holographic processors based on the material characteristics of LiNbO3 is introduced. The processors rely on holographic subtraction to detect differences in optical wavefronts that are spatially modulated to reflect either incoming or reference information. The state of the art of their fabrication and performance is described in the following paper. This paper outlines the principles of holography and photorefractivity that make these processors possible. Particular emphasis is placed on a potential mode of operation termed self-subtraction, in which the holographic processor is able to adapt to changes in reference information without the need for commands from an external operator.

Vahey, D. W.↗
NASA NTRS1981

Magnitude and frequency of wind speed shears from 3 to 150 meters

An analysis is presented of high resolution wind profile measurements recorded at the NASA 150-m ground winds tower facility, showing wind speed shear frequency and magnitude distributions for six vertical layers of the atmosphere and one vertical distance. Vertical wind shear is defined as the change of wind speed with height, and its magnitudes were derived by algebraically subtracting lower level wind speeds from those of higher levels and dividing the distance between levels. Horizontal wind shear is understood to be change of wind speed with horizontal distance, and its magnitudes were derived by algebraically subtracting the wind speed at a short tower from that at a tall one and dividing by the distance between towers.

Alexander, M. B.↗
NASA NTRS1982

Electromagnetic deep-probing (100-1000 KMS) of the Earth's interior from artificial satellites: Constraints on the regional emplacement of crustal resources

The two stages of analysis of MAGSAT magnetic data which are designed to evaluate electromagnetic induction effects are described. The first stage consists of comparison of data from contiguous orbit passes over large scale geologic boundaries, such as ocean-land interfaces, at several levels of magnetic disturbance. The purpose of these comparisons is to separate induction effects from effects of lithospheric magnetization. The procdure for reducing the data includes: (1) identifying and subtracting quiet time effects; (2) modelling and subtracting first order ring current effects; and (3) projecting an orbit track onto a map as a nearly straight line so it can serve as an axis on which to plot the corresponding orbit pass data in the context of geography. The second stage consists of comparison of MAGSAT data with standard hourly observatory data. The purpose is to constrain the time evolution of ionospheric and magnetospheric current systems. Qualitative features of the ground based dataset are discussed. Methods for reducing the ground based data are described.

Hermance, J. F.↗
NASA NTRS1982

Analysis of two Seasat synthetic aperture radar images of an urban scene

Because the Seasat satellite is not polar-orbiting, the look-directions of its SAR radar on the basic ascending and descending orbits were neither in the same direction, orthogonal to, nor opposite to, one another. This calls for a technique by means of which to identify those features within a given geographic region which were imaged from two directions by Seasat SAR and are sensitive to radar orientation. It is demonstrated that images from the two orbits with different look directions can be registered and subtracted from one another, with the resulting difference image highlighting those features that are direction-sensitive. Although this depends on a precise registration the subtraction technique is straightforward once such registration has been obtained.

Bryan, M. L.↗
NASA NTRS1984

Positive-feedback photometric drift in the PDS

Digitizing flatfield images produces conditions in the Photometric Data System PDS which cause the measured density to drift by as much as .1 DN during a 10 minute interval. The drift occurs when the PDS, set up in equilibrium at fog level, subsequently scans a reasonably dense region for periods of longer than a few minutes. The drift is manifested primarily as a positive shift in density that is approximately the same for all densities. If the fog level is assumed to be in fact constant and is monitored during scans of flat fields, the PDS drift may be removed by subtracting the difference between the observed fog level and its assumed constant value for each pixel. This function is then smoothed and subtracted, as a function of scan line, from the measured density. The fog level is then adjusted to a standard value by adding a constant. The result is a flattened scan with PDS drift removed to the accuracy within which the fog level drift matches the drift at other levels.

Cornett, R. H.↗
NASA NTRS1986

Calculating Bearing Forces From Strain-Gage Signals

Technique for obtaining force components on cylindrical bearing holder uses pairs of opposing strain gages. Signals proportional to outputs of pairs of opposing gages subtracted from each other. Subtraction nearly eliminates crosstalk between orthogonal force components. Signal-processing technique equally applicable to rotating as well as stationary loads.

Fenwick, J. R.↗
NASA NTRS1985

Solar modulation and interplanetary gradients of the galactic electron flux, 1977 - 1984

The flux of electrons with energy from approximately 10 to 180 MeV measured ith the electron telescope on the Voyager 1 and 2 spacecraft in the heliocentric radial range 1 to 22 AU between 1977 and 1984 is reported. Jovian electrons were clearly observable between 1978 and 1983 (radial range 2 to 12 AU) at energies below approximately 50 MeV. Above approximately 50 MeV the electron intensity exhibited temporal variations generally related to the 11 year modulation of protons 75 MeV. The overall magnitude of the electron intensity changes between the maximum intensity observed in 1977 and the minimum intensity in 1981 was a factor approximately 2, also comparable to that observed for 75 MeV protons. By early 1985 the electron intensity has apparently recovered to the level observed in 1977 whereas the proton intensity was still about 20% lower. A detailed interpretation of these electron variations in all energy channels depends on an accurate subtraction of background induced by energetic protons of a few 100 Mev. This subtraction is facilitated by calibration results at several energies. Further results on these temporal variations and limits on possible interplanetary gradients will be reported.

Christon, S. P.↗
NASA NTRS1985

Solar modulation and interplanetary gradients of the galactic electrons flux, 1977 - 1984

The flux of electrons with energy from approx. 10 to 180 MeV measured with the electron telescope on the Voyager 1 and 2 spacecraft in the heliocentric radial range 1 - 22 AU between 1977 and 1984 is reported. Jovian electrons were clearly observable between 1978 and 1983 (radial range 2 - 12 AU) at energies below approx. 50 MeV. Above approx. 50 MeV the electron intensity exhibited temporal variations generally related to the 11 year modulation of protons 75 MeV. The overall magnitude of the electron intensity changes between the maximum intensity observed in 1977 and the minimum intensity in 1981 was a factor approx. 2, also comparable to that observed for 75 MeV protons. By early 1985 the electron intensity had apparently recovered to the level observed in 1977 whereas the proton intensity was still about 20% lower. A detailed interpretation of these electron variations in all energy channels depends on an accurate subtraction of background induced by energetic protons of a few 100 MeV. This subtraction is facilitated by calibration results at several energies.

Christon, S. P.↗
NASA NTRS1986

Evidence for a low-density component in the broad-line region of Seyfert 1 galaxies

It is found that the forbidden 4959-5007 A broad O III lines, good candidates for the excess shelf emission, are found in the vicinity of H-beta in Seyfert 1 galaxy spectra. The shelf-study method used to remove Fe II assumes that the profiles of the contributors to the shelf are known, and that subtraction of these contributors in the correct amount will result in a fairly smooth H-beta profile. Data were obtained with the Ohio State University Image-Dissector Scanner with a 600 line/mm grating, on a 1.8-m reflector. The estimated cloud electron density of 1 billion/sq cm is at the low end of those used for BLR photoionization models. The presence of a broad residual emission feature in the neighborhood of 5050 A after subtraction of the shelf is thought to be the result of a weak broad emission in this range from yet another species.

Crenshaw, D. M.↗
NASA NTRS1986

Microcomputer-based programmable optical signal processor

A microcomputer-based real-time programmable optical signal processing system utilizing a magneto-optic spatial light modulator (MOSLM) and a liquid crystal light valve (LCLV) is described. This system can perform a myriad of complicated optical operations, such as image correlation, image subtraction, and matrix multiplication. Its important asserts are its programmability and the capability of real-time addressing. These are important for telerobotic vision in space automation applications. Design specifications and suggestions for practical implementation of the system are discussed. Some preliminary experimental demonstrations are conducted to demonstrate applications of the proposed system to image correlation for optical pattern recognition, image subtraction for lC chip inspection, and matrix multiplication for optical computing.

Yu, F. T. S.↗
NASA NTRS1986

Comet P/Halley 1910, 1986: An objective-prism study

V. M. Slipher of the Lowell Obs. collected a large amount of spectroscopic data during the 1910 apparition of Halley's comet. Three of his post perihelion objective-prism plates were selected, digitized, and subjected to modern digital data reduction procedures. Some of the important steps in the analysis where: (1) Density to intensity conversion for which was used 1910 slit spectra of Fe-arc lamp on similar plates (Sigma) and derived an average characteristic curve; (2) Flux calibration using the fact that during the period June 2 to 7 1910 P/Halley was very close (angular distance) to the bright star Alpha Sex (A0III, V-4.49), and the spectra of both star and comet were recorded on the same plates. The flux distribution of Alpha Sex was assumed to be similar to that of the standard star 58 Aql and derived a sensitivity curve for the system; (3) Atmospheric extinction using the standard curve for the Lowell Obs.; (4) Solar continuum subtraction using the standard solar spectrum binned to the spectral resolution. An example of a flux-calibrated spectrum of the coma (integrated over 87,000km) before the subtraction of solar continuum is presented.

Carsenty, U.↗
NASA NTRS1987

Narrowband imaging and spectroscopy close to the nucleus of the Seyfert galaxy NGC 7682

Keel's (1985) report of a jet-like optical feature emanating from the nucleus of NGC 7682 is investigated. Deep CCD images of NGC 7682 were taken with narrowband filters centered on the redshifted wavelength of H-alpha + forbidden N II and on a nearby continuum region. The continuum-subtracted line images show no evidence of the jet feature, although numerous H II regions appear clearly, both close to the nucleus and in the extended spiral arm structure. Spectra were taken at various dispersions and position angles, including the supposed position angle of the jet. These data were used to obtain background-subtracted spectra at the precise location of the jet. No excess emission was detected above the background-galaxy contribution. The highest-resolution spectra were used to determine the redshift of the galaxy to high precision.

Brodie, Jean↗
NASA NTRS1987

Fourier removal of stripe artifacts in IRAS images

By working in the Fourier plane, approximate removal of stripe artifacts in IRAS images can be effected. The image of interest is smoothed and subtracted from the original, giving the high-spatial-frequency part. This 'filtered' image is then clipped to remove point sources and then Fourier transformed. Subtracting the Fourier components contributing to the stripes in this image from the Fourier transform of the original and transforming back to the image plane yields substantial removal of the stripes.

Van Buren, Dave↗
NASA NTRS1990

Limits to derived flare properties using estimates for the background fluxes - Examples from GOES

A method has been presented for restricting the random derived flare temperatures and emission measures. The method is based on three tests and is applicable not only to disk-integrated observations, but also for any high-resolution observations that cannot distinguish the emissions from flaring and nonflaring plasma. The first two tests are based on the assumption that both the temperature and the emission measure should increase as the flare flux rises. The third assumes that the preflare temperature of the plasma that flares should exceed the temperature averaged over all other emitting sources. These tests were applied to two solar flares to illustrate the improvements in the derived flare properties. It is shown that flare properties do not always lie between those derived by the use or subtraction of the total preflare flux. The flare properties can, however, be bounded by subtracting and using the long- and short-wavelength preflare fluxes, respectively.

Bornmann, P. L.↗