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At least 253 records · Page 14

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NASA NTRS1979

Linear feature selection with applications

Several ways in which feature selection techniques were used in LACIE are discussed. In all cases, the methods require some a priori information and assumptions; in most, the classification procedure (Bayes optimal) was chosen in advance. The transformations used for dimensionality reduction are linear, that is, the variables in feature space are always linear combinations of the original measurements. Several numerically tractable criteria developed for LACIE, which provide information about the probability of misclassification, are discussed. Recent results on linear feature selection techniques are included. Their use in LACIE is discussed. Related open questions are mentioned.

Decell, H. P., Jr.↗

NASA NTRS1979

Unidentified infrared spectral features

It is noted that the infrared spectra between 2 and 13 microns of a variety of objects have become available in the past few years. Attention is given to the fact that these spectra have shown many objects to have up to six emission features that are still unidentified. It is reported that other objects show absorptions due to ice, carbon monoxide, silicates, and two unidentified features. Discussion covers the observational characteristics of the unidentified features together with possible identifications.

Willner, S. P.↗

NASA NTRS1979

An absorption feature in the spectrum of the pulsed hard X-ray flux from 4U0115 + 63

A spectral feature, apparently an absorption line, has been observed at an energy of 20.1 + or - 0.5 keV in the pulsed flux of the 3.61-s X-ray pulsar 4U 0115+63 by using the UCSD/MIT instrument on HEAO 1. The line strength, expressed as equivalent width, is 3.1 + or - 0.5 keV. Although essentially unresolved, the feature has a depth more than 60% of the continuum flux. If the feature arises by cyclotron resonance absorption near the magnetic poles of the neutron star, it implies a magnetic field of between approximately 1.8 and 2.5 x 10 to the 12th G, depending on the gravitational redshift (no more than about 5-40%).

Wheaton, W. A.↗

NASA NTRS1981

A far-infrared emission feature in carbon-rich stars and planetary nebulae

The 16-30 micron spectra of several carbon stars and the planetary nebulae IC 418 and NGC 6572 have been obtained using the NASA C-141 Kuiper Airborne Observatory. A newly observed emission feature appears in the spectrum of IRC +10216 and several other carbon stars at wavelengths greater than 24 microns. The feature is interpreted as resulting from a solid-state resonance in the dust grains which have condensed around these stars. A similar feature appears in the spectra of IC 418 and NGC 6572, implying that the same type of dust is present. Since the dust probably condensed from a carbon-rich gas, this indicates an evolutionary link between carbon stars and these planetary nebulae. No identification for the grain material has been found, but some clues are apparent which could aid in the identification.

Forrest, W. J.↗

NASA NTRS1982

Report of subpanel on feature extraction

The state of knowledge in feature extraction for Earth resource observation systems is reviewed and research tasks are proposed. Issues in the subpixel feature estimation problem are defined as: (1) the identification of image models which adequately describe the data and the sensor it is using; (2) the construction of local feature models based on those image models; and (3) the problem of trying to understand these effects of preprocessing on the entire process. The development of ground control point (GCP) libraries for automated selection presents two concerns. One is the organization of these GCP libraries for rectification problems, i.e., the problems of automatically selecting by computer the specific GCP's for particular registration tasks. Second is the importance of integrating ground control patterns in a data base management system, allowing interface to a large number of sensor image types with an automatic selection system. The development of data validation criteria for the comparison of different extraction techniques is also discussed.

Source record↗

NASA NTRS1982

Identification of the emission features near 3.5 microns in the pre main sequence star HD 97048

The spectrum of HD97048 was measured with a resolving power of 450 between 3.37 and 3.64 microns. The prominent feature near 3.5 microns is well resolved, with a peak at 3.53 microns and a wing extending to a shorter wavelength. The weaker feature near 3.4 microns is found to peak at 3.43 microns, in contrast to the 3.40 micron feature seen in other astronomical objects. The observed spectrum strongly resembles laboratory spectra of mixtures of monomeric and dimeric formaldehyde embedded in low temperature solids. Of various possible excitation mechanisms, ultraviolet pumped infrared fluorescence of formaldehyde in interstellar grains provides the best explanation for the observed spectrum of HD 97048.

Baas, F.↗

NASA NTRS1982

High-spectral-resolution observations of the 7.7-micron feature in HD 44179

Observations of the moon and HD 44179 were obtained in the wavelength range of 7.5-8.5 microns at a resolving power of approximately 800. The spectrum of the moon shows absorptions caused by telluric methane. Use of the moon as a calibrator is effective in removing these atmospheric lines. The spectrum of HD 44179 shows that the 7.7-micron emission feature does not break up into discrete, resolved emission features. Instead, it must be a broad, apparently continuous, emission feature.

Russell, R. W.↗

NASA NTRS1982

Detection of pedestal features in dark clouds - Evidence for formation of low mass stars

To assess whether B335 is unique among dark clouds or whether CO-12 pedestal features are quite common, 180 opacity class 5 and 6 Lynds clouds were surveyed. From this set of data, three additional sources were found to have pedestal features. These suggest the presence of embedded low-mass stars, though a hot differentially rotating disk cannot be excluded for B335. Estimates of the mass-loss rate required to produce stellar winds consistent with observations are comparable with mass-loss rates for T Tauri stars. Further, the pedestal feature formation rate is similar to the local low-mass star formation rate.

Frerking, M. A.↗

NASA NTRS1982

Observations of the 30 micron feature in IRC + 10216

Infrared observations from 30 to 37 microns of IRC+10216 extend the wavelength coverage of the 30-micron feature found in four carbon stars and two planetary nebulae by Forrest, Houck, and McCarthy (1981). The present data confirm the existence of this newly observed feature and determine its shape beyond 30 microns. The determination of the long-wavelength end of the spectral excess depends critically on the assumed underlying continuum. A combined spectrum of the excess is presented and shows the feature to extend to at least 37 microns.

Herter, T.↗

NASA NTRS1982

Time variations of an absorption feature in the spectrum of the gamma-ray burst on 1980 April 19

The photon number spectrum integrated over the impulsive part of the event is shown to fit a thermal bremsstrahlung function with a temperature of 330 + or - 70 keV at energies between 151 and 487 keV. At lower energies, the data points lie considerably below this function, indicating a broad absorption feature extending down to values less than or equal to 28 keV, the lowest energy measured. The upper energy of this absorption feature varies from 100 to 150 keV on a time scale less than or equal to 0.5 s. This event is interpreted as a typical gamma ray burst, even though it is still considered remotely possible that it is of solar origin. The spectral features, together with their variability, are interpreted in terms of electron interactions at the cyclotron resonance frequency in magnetic fields of 10 to the 12th - 10 to the 13th gauss close to the surface of a neutron star.

Dennis, B. R.↗

NASA NTRS1983

Autonomous earth feature classification - Shuttle and aircraft flight test results

The Feature Identification and Location Experiment (FILE) flown on the Shuttle STS-2 mission November 12-14, 1981, tested a technique for autonomous real-time classification of selected earth features, i.e., water; bare land; vegetation; and clouds, snow, and ice. A second instrument, designed for aircraft flights, flew over regions of the west and east coasts of the United States and across the country. In each instrument, two bore-sighted CCD cameras image earth scenes in two spectral bands. Each camera includes a 100-element by 100-element detector array, and classification circuits. A simple algorithm and logic circuit provides classification decisions within a few microseconds. The experiment records the number of picture elements (pixels) representing each feature and the reflected solar radiation for each band. After flight, pixel-by-pixel classification images are constructed and compared with 70-mm color photographs taken simultaneously with the CCD-camera data.

Sivertson, W. E., Jr.↗

NASA NTRS1983

Mass loss, levitation, accretion, and the sharp-lined features in hot white dwarfs

A study has been conducted of eight white dwarfs, including seven DA and one He-rich types. The study is based on high-resolution observations conducted with the aid of the International Ultraviolet Explorer. Four of the dwarfs show features related to heavy elements which are not interstellar in origin. It is tentatively suggested that, at least in the hottest low-gravity DA white dwarfs, the observed narrow-lined features are formed in expanding halos or winds associated with the white dwarfs. Theoretically, stable white dwarf halos should actually be coronae with temperatures in excess of 1,000,000 K. However, the observed narrow-lined features do not suggest such high temperatures. The observed radial velocities suggest weak stellar winds in two hot white dwarfs, namely, G191-B2B and 2111+49. It is tentatively proposed that radiative levitation can explain the appearance of the observed metallic lines in the hot DA white dwarfs.

Bruhweiler, F. C.↗

NASA NTRS1984

Elysium Region, Mars: Characterization of tectonic features

In this paper the tectonic features of the Elysium region are identified and characterized. Identification of features was made using USGS controlled photomosaics (Elysium quadrangle, and portions of Amenthes and Cebrenia quadrangles); Viking Orbiter photographic data were used in individual cases to assist in identification. The positions and orientations of tectonic features can then be used, in conjunction with estimates of the mass of the volcanic load obtained from gravity modelling, to constrain the thickness of the elastic lithosphere in the region.

Hall, J. L.↗

NASA NTRS1983

Sharp shortward-shifted features in the spectra of O subdwarfs

Preliminary inspection of archival high-dispersion ultraviolet spectra obtained by the International Ultraviolet Explorer reveal sharp shortward-shifted features in the spectra of O subdwarfs. In three examples presented here, BD + 75.325 deg, HD 128220 B, and BD + 28.4211 deg, stable, multiple, discrete shortward-shifted components of the N V, C IV, and Si IV resonance doublets are seen. The available data suggest that some of these features are persistent, being relatively stable in velocity and intensity over at least 9 months. It is tentatively suggested that the mechanism, or mechanisms, producing these discrete features operates universally in hot stars, from luminous O and B stars down through the O subdwarfs to include the hot white dwarfs. If true, this has important ramifications for current knowledge of mass loss in hot stars.

Bruhweiler, F. C.↗

NASA NTRS1985

The Use of Linear Feature Detection to Investigate Thematic Mapper Data Performance and Processing

The geometric and radiometric characteristics of thematic mapper data through analysis of linear features in the data are investigated. The particular aspects considered are: (1) thematic mapper ground IFUV; (2) radiometric contrast between linear features and background; (3) precision of system geometric correction; (4) band-to-band registration; and (5) potential utility of TM data for linear feature detection especially as compared to MSS data. It is shown that TM data may be used to estimate TM pixel size illustrate band: band mis-registration.

Gurney, C. M.↗

NASA NTRS1984

Methods to recover the narrow Dicke sub-Doppler feature in evacuated wall-coated cells without restrictions on cell size

The hyperfine resonance observed in evacuated wall-coated cells with dimensions lambda/2 (lambda is the hyperfine resonance wavelength) consists of a narrow Dicke sub-Doppler linewidth feature, the spike, superimposed on a broad pedestal. The hydrogen maser provides a classic example of this lineshape. As cell size is increased, an effect unique to evacuated wall-coated cells occurs. Certain combinations of microwave field distribution and cell size result in a lineshape having a pedestal with a small spike feature or only the broad pedestal with no spike. Such conditions are not appropriate for atomic frequency standard applications. The cause of the evacuated wall-coated cell lineshape is reviewed and methods to recover the narrow spike feature without restrictions on cell size is discussed. One example is a cell with dimensions having equal volumes of exposure to opposite phases of the microwave magnetic field.

Robinson, H. G.↗

NASA NTRS1984

Development of a quantitative basis for selection of spectral features in a vegetation monitoring system

The development of an objective methodology for evaluation of alternative Landsat data preprocessing options, spectral transform features for monitoring vegetation, and feature summarization algorithms is presented. Based on estimates of spectral separability between a target class and its confusion classes, analysis of variance techniques are used to evaluate potential design options for large scale vegetation monitoring systems. Case studies are presented for early season and through the season spring small grains separation and for barley/other spring small grains separation. It is concluded that a basis for efficient, objective selection among alternative feature extraction approaches has been established for the large scale vegetation mapping/inventory problem. Although the approach has been demonstrated for the unitemporal class separability case, extensions to the multitemporal case are under development.

Phinney, D. E.↗

NASA NTRS1985

Identification of the 1400 and 1600 A features observed in the ultraviolet spectra of DA white dwarfs

The 600 A absorption feature in the spectra of cool DA white dwarf stars has been identified as a resonance broadening of Ly-alpha due to the hydrogen quasi molecule. Likewise, the 1400 A absorption feature in the spectra of cool and moderately warm DA white dwarf stars appears to be due to a Ly-alpha satellite line arising from the hydrogen ion quasi molecule. The strength of both features is gravity sensitive and therefore promises to be an excellent indicator of surface gravity.

Nelan, E. P.↗