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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Low-cost solar array project: Four absolute cavity radiometer (pyrheliometer) intercomparisons at New River, Arizona: Radiometer standards

Four detailed intercomparisons were made for a number of models of cavity-type self-calibrating radiometers (pyrheliometers). Each intercomparison consisted of simultaneous readings of pyrheliometers at 30-second intervals in runs of 10 minutes, with at least 15 runs per intercomparison. Twenty-seven instruments were in at least one intercomparison, and five were in all four. Summarized results and all raw data are provided from the intercomparisons.

Estey, R. S.↗
NASA NTRS1981

Flame structure in a swirl stabilized combustor inferred by radiant emission measurements

Results of measurements of time-averaged chemiluminescent emissions from CH, OH, and CO2 and of Na tracer emissions along lateral lines-of-sight through a cylindrical premixed, swirl-stabilized combustor are reported. Assuming axial symmetry and small optical depth, raw data are inverted to obtain local emission levels from these species as a function of radius. The chemiluminescent emissions are interpreted as signatures of chemical reaction and used in determining the regions of reactions and heat release in the combustor. The data are compared with composition and velocity data obtained in the combustor for identical operating conditions. The results demonstrate that reaction occurs in a relatively narrow, turbulent flame-like combustion zone which begins upstream of the time-averaged location of the swirl-induced recirculation zone and propagates around and laterally away from the recirculation zone into the unburned gas.

Beyler, C. L.↗
NASA NTRS1982

Intercomparison of lunar laser and traditional determinations of earth rotation

Since August, 1969, ranges to one or more retroreflector arrays on the lunar surface have been measured by means of a laser procedure. Analysis of these measurements improves determination, not only of the orbit and librations of the moon, but also of the rotational parameters of the earth, including the X and Y coordinates of the terrestrial pole, and the true rotational angle of the earth with respect to atomic or to broadcast time. The considered approach for deriving the Universal Time 1 (UT1) involves two steps. During the first step the parameters of the lunar orbit and librations are solved along with the coordinates of the retroreflectors on the moon and of the observatory. Improved values of the Universal Time 0 (UT0) and range corrections at the observatory are obtained in the second step. Attention is given to lunar laser ranging (LLR), raw data in UT1, an harmonic analysis of the LLR UT1 data, and data obtained in 1980. The results provide UT1 with an accuracy of a factor of 2 or more better than was previously available from conventional astrometric data.

Fliegel, H. F.↗
NASA NTRS1982

Turbulence measurements in a swirling confined jet flowfield using a triple hot-wire probe

An axisymmetric swirling confined jet flowfield, similar to that encountered in gas turbine combustors was investigated using a triple hot-wire probe. The raw data from the three sensors were digitized using ADC's and stored on a Tektronix 4051 computer. The data were further reduced on the computer to obtain time-series for the three instantaneous velocity components in the flowfield. The time-mean velocities and the turbulence quantities were deduced. Qualification experiments were performed and where possible results compared with independent measurements. The major qualification experiments involved measurements performed in a non-swirling flow compared with conventional X-wire measurements. In the swirling flowfield, advantages of the triple wire technique over the previously used multi-position single hot-wire method are noted. The measurements obtained provide a data base with which the predictions of turbulence models in a recirculating swirling flowfield can be evaluated.

Janjua, S. I.↗
NASA NTRS1983

Cloud cover typing from environmental satellite imagery. Discriminating cloud structure with Fast Fourier Transforms (FFT)

The use of two dimensional Fast Fourier Transforms (FFTs) subjected to pattern recognition technology for the identification and classification of low altitude stratus cloud structure from Geostationary Operational Environmental Satellite (GOES) imagery was examined. The development of a scene independent pattern recognition methodology, unconstrained by conventional cloud morphological classifications was emphasized. A technique for extracting cloud shape, direction, and size attributes from GOES visual imagery was developed. These attributes were combined with two statistical attributes (cloud mean brightness, cloud standard deviation), and interrogated using unsupervised clustering amd maximum likelihood classification techniques. Results indicate that: (1) the key cloud discrimination attributes are mean brightness, direction, shape, and minimum size; (2) cloud structure can be differentiated at given pixel scales; (3) cloud type may be identifiable at coarser scales; (4) there are positive indications of scene independence which would permit development of a cloud signature bank; (5) edge enhancement of GOES imagery does not appreciably improve cloud classification over the use of raw data; and (6) the GOES imagery must be apodized before generation of FFTs.

Logan, T. L.↗
NASA NTRS1984

Description of sunspot cycles by orthogonal functions

Based on the principal component analysis technique and evidence for a 22-yr double-sunspot cycle periodicity. The time series of sunspot numbers is represented as a sum of mutually orthogonal eigenvectors in the time domain. It is shown that the first two eigenvectors account for about 90 percent of the cumulative 'signal power,' and that this is sufficient for reconstruction of the raw data curve. It is also noted that the second eigenvector behaves as the time derivative of the first, and that a phase-plane plot of these eigenvectors (i.e. a plot of a variable vs. its rate of change) suggests that the sun's sunspot cycle is driven by an oscillator; the implication is that, embedded within the sun, a chronometer is at work (e.g. Dicke, 1979).

Teuber, D. L.↗
NASA NTRS1986

Performance of the SIR-B digital image processing subsystem

A ground-based system to generate digital SAR image products has been developed and implemented in support of the SIR-B mission. This system is designed to achieve the maximum throughput while meeting strict image fidelity criteria. Its capabilities include: automated radiometric and geometric correction of the output imagery; high-precision absolute location without tiepoint registration; filtering of the raw data to remove spurious signals from alien radars; and automated catologing to maintain a full set of radar and image production facility in support of the SIR-B science investigators routinely produces over 80 image frames per week.

Curlander, J. C.↗
NASA NTRS1987

Summary of paper: Area navigation implementation for a microcomputer-based Loran-C receiver

The development of an area navigation program and the implementation of this software on a microcomputer-based Loran-C receiver to provide high-quality, practical area navigation information for general aviation are described. This software provides range and bearing angle to a selected waypoint, cross-track error, course deviation indication (CDI), ground speed, and estimated time of arrival at the waypoint. The range/bearing calculation, using an elliptical Earth model, provides very good accuracy; the error does not exceed more than -.012 nm (range) or 0.09 degree (bearing) for a maximum range to 530 nm. The alpha-beta filtering is applied in order to reduce the random noise on Loran-C raw data and in the ground speed calculation. Due to alpha-beta filtering, the ground speed calculation has good stability for constant or low-accelerative flight. The execution time of this software is approximately 0.2 second. Flight testing was done with a prototype Loran-C front-end receiver, with the Loran-C area navigation software demonstrating the ability to provide navigation for the pilot to any point in the Loran-C coverage area in true area navigation fashion without line-of-sight and range restriction typical of VOR area navigation.

Oguri, Fujiko↗
NASA NTRS1987

Development of N-version software samples for an experiment in software fault tolerance

The report documents the task planning and software development phases of an effort to obtain twenty versions of code independently designed and developed from a common specification. These versions were created for use in future experiments in software fault tolerance, in continuation of the experimental series underway at the Systems Validation Methods Branch (SVMB) at NASA Langley Research Center. The 20 versions were developed under controlled conditions at four U.S. universities, by 20 teams of two researchers each. The versions process raw data from a modified Redundant Strapped Down Inertial Measurement Unit (RSDIMU). The specifications, and over 200 questions submitted by the developers concerning the specifications, are included as appendices to this report. Design documents, and design and code walkthrough reports for each version, were also obtained in this task for use in future studies.

Lauterbach, L.↗
NASA NTRS1986

Dead-time effects in pulse-counting Digicon detectors

The Hubble Space Telescope's High Resolution Spectrograph employs two pulse-counting Digicon detectors to record UV spectra. At higher measured count rates, the intervals between photon arrivals become comparable to the response time of the electronics, so that not every pulse will be counted; this 'paired pulse' effect causes departures from linearity and must be corrected for during raw data reduction. Attention is given to two analytic equations that quantify the dead-time losses. The less attenuated spectra are noted to be severely distorted by these losses; a comparison with the undistorted low count rate data allows a detailed analysis to be made of the pulse-counting characteristics over five decades of input event rates. The present equations and calibration methods should be applicable to all kinds of multichannel pulse-counting detectors.

Ebbets, Dennis C.↗
NASA NTRS1986

Conceptual design of the High-Resolution Imaging Spectrometer (HIRIS) for EOS

The design concept and practical realization of HIRIS, the imaging spectrometer being developed for the Space Station Earth Observation System (EOS) on the basis of the Shuttle Imaging Spectrometer Experiment (SISEX), are discussed. Nominal operating parameters for HIRIS include altitude 705 km, GIFOV 30 m, swath 48.4 km, spectral sampling interval 10 nm, spectral coverage 400-2450 nm, cross-track pointing +20/-20 deg, down-track pointing +60/-30 deg, and raw data rate (at 8 bits/pixel) 621 Mb/s. The f/1.9 optical configuration for HIRIS is shown in a drawing, and consideration is given to technological challenges being encountered in modifying the SISEX focal-plane detectors, data-reduction procedures, and cooling system to meet the HIRIS requirements.

Herring, Mark↗
NASA NTRS1987

The high resolution imaging spectrometer (HIRIS) for EOS

The HIRIS is designed to acquire images in 196 spectral bands simultaneously in the 0.4-2.5 micron wavelength region. HIRIS is a targeting rather than a continuous acquisition instrument and obtains high spatial and spectral resolution images in a 23 km swath with a 30 m GIFOV in vertical viewing. Gimbal pointing is proposed which will allow image acquisition at -30 + 60 deg down-track and + or - 25 deg cross-track. The raw data rate of the instrument is 393 Mbs. The high spectral resolution will make it possible to directly identify surficial materials such as rocks, soils, and suspended matter in water, and HIRIS opens up the possibility of studying biogeochemical processes in vegetation canopies. HIRIS will be used in conjunction with MODIS as a multistage sampling system.

Goetz, Alexander F. H.↗
NASA NTRS1987

In-orbit calibration adjustment of the Nimbus-7 SMMR

The procedure for converting raw antenna signals (counts) from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) to microwave radiances is described. The procedure entails taking the raw data stored on TAT data tapes, applying an interim prelaunch calibration, correcting for polarization mixing, and finally adjusting the calibration so that the observations conform to model calculations of oceanic radiances. The results are stored on TCT data tapes with the same format as the TATs, i.e., the basic sampling interval of the SMMR is retained. The properties of the TCTs are compared with those of the other basic SMMR radiance data product, the CELL tapes, in which the integrated fields-of-view (IFOVs) have been averaged into cells with coarser sampling intervals and in which the prelaunch calibration is the final one used.

Gloersen, Per↗
NASA NTRS1985

Constitutive modeling for isotropic materials

The first year of progress on a NASA-Lewis contract with the General Electric Co is documented. The purpose of this contract (NAS3-23927) is to develop and evaluate unified constitutive equations for applications to hot-path components of aircraft gas turbine engines such as high pressure turbine blades and vanes. To accomplish this goal, uniaxial, notched, and multiaxial specimens made of conventionally cast Rene 80 are being tested under conditions that simulate engine operating conditions. To reduce the raw data, automated data reduction techniques are being developed that produce computer files containing the information needed to analyze proposed constitutive theories. Described are the analytical methods being developed to determine the parameters for these nonlinear unified theories by using the reduced data files. In another activity, a dedicated finite-element computer code is being developed to use unified theories in the structural analysis of hot-section components. This code was extensively verified for one such theory by successfully predicting the strain histories measured experimentally at the notch root of complex specimens taken from complex laboratory specimens.

Ramaswamy, V. G.↗
NASA NTRS1988

Observations of F- and P-Mode Oscillations of High Degree (500 Is Less Than L Is Less Than 2500) in Quiet and Active Sun

Spectra (l - v diagrams) from high resolution observations taken at the Vacuum Tower Telescope (NSO/Sunspot) are presented. The raw data are CCD images taken through the SOUP narrowband filter in Fe I 5576 A. Four filtergrams spaced through the spectral line are combined to form velocity movies. Spectra for 80 min of data with 0.5 to 1.5 arcsec resolution are presented for the entire field-of-view and for quiet and magnetic (plage) subregions. Ridges f and p1 to p5 are evident in velocity spectra, extending to l = 2500 (f), l = 1800 (p1), and l = 1200 (p2). Much less power is seen in the magnetic region than in the quiet Sun. Three-dimensional Fourier filtering shows that oscillation velocity amplitude drops sharply at the boundary of the active region for each family of modes considered.

Tarbell, T. D.↗
NASA NTRS1989

The high resolution imaging spectrometer (HIRIS) for EOS

The high resolution imaging spectrometer (HIRIS) designed for the Earth Observing System (EOS) is designed to acquire images in 192 spectral bands simultaneously in the 0.4-2.5-micron wavelength region. HIRIS is a targeting rather than a continuous acquisition instrument and obtains high-spatial- and spectral-resolution images in a 30-km swath with a 30-m ground instantaneous field of view (GIFOV) in vertical viewing. Pointing will allow image acquisition at -30 to +60 deg along-track and +/-24 deg cross-track. The raw data rate of the instrument is 512 Mbs. The high spectral resolution will make it possible to identify many surficial materials such as rocks, soils, and suspended matter in water directly. HIRIS also offers the possibility of studying biochemical process in vegetation canopies.

Goetz, Alexander F. H.↗
NASA NTRS1988

The design and performance of a modem for land mobile satellite communications

The digital implementation and performance of a multipath fade-tolerant differentially coherent 8-PSK-based modem for a land mobile satellite experiment (MSAT-X) program is described. At the receiver, differential detection using a matched filter arrangement and feedforward Doppler compensation is employed to achieve several operational benefits. For this L-band satellite link, the channel utilization is an efficient 1.0 bps/Hz for raw data and 1.5 bps/Hz for coded data. The experimental data analysis shows that the modem functions over the fading channel and performs within 1 dB of theoretical or simulation estimates.

Jedrey, T. C.↗
NASA NTRS1988

Compression of high spectral resolution imagery

The Earth Orbiting Satellite (EOS), scheduled for launch in the mid-1990s, will include a next-generation multispectral imaging system (HIRIS) having unprecedented spatial and spectral resolution. Its high resolution, however, comes at the cost of a raw data rate which exceeds the communication channel capacity assigned to the entire EOS mission. This paper explores noisy compression algorithms which may compress multispectral data by up to 30:1 or more. Algorithm performance is measured using both traditional and mission-oriented criteria (e.g., feature classification consistency). It is shown that vector quantization, merged with suitable preprocessing techniques, is the most viable candidate.

Baker, Richard L.↗