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At least 289 records · Page 16

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NASA NTRS1978

Spatial structure in lines in the 3398-3526 A region at the extreme limb - Observation, identification and interpretation

Spectrograms of high spatial and spectral resolution have been obtained of the extreme solar limb, using the vacuum tower telescope of Sacramento Peak Observatory. Emission lines in the range 3398-3526 A have been identified and classified according to intensity, spatial structure (intensity variation), and profile. Some lines show spatial intensity variation; others do not. It is shown that this effect is related to the abundance of the element responsible for the line and the mean lower-level excitation potential of interlocked lines. This effect is explained in terms of radiative interlocking with other lines, as well as the characteristic size of the volume contributing to the mean intensity.

Canfield, R. C.↗

NASA NTRS1979

Electron impact on atmospheric gases. III - Spatial yield spectra for N2

Spatial yield spectra have been calculated for electron energy degradation into molecular nitrogen gas using a Monte Carlo method for 0.1- to 5.0-keV incident electrons. The spectra contain the spatial yield information about the electron degradation process and can be employed to calculate a 'yield' for any inelastic state at any position in the medium. Because of the spectrum's useful nature and simple characteristics, the three-variable spatial yield spectrum U(E, z, E sub zero) is analytically represented as well. This analytic form can then be easily applied to atmospheric and laboratory problems dealing with energetic electron degradation.

Jackman, C. H.↗

NASA NTRS1979

Spatial distribution of large-scale solar magnetic fields and their relation to the interplanetary magnetic field

The spatial organization of the observed photospheric magnetic field as well as its relation to the polarity of the IMF have been studied using high resolution magnetograms from the Kitt Peak National Observatory. Systematic patterns in the large scale field are due to contributions from both concentrated flux and more diffuse flux. The polarity of the photospheric field, determined on various spatial scales, correlates with the polarity of the IMF. Analyses based on several spatial scales in the photosphere suggest that new flux in the interplanetary medium is often due to relatively small photospheric features which appear in the photosphere up to one month before they are manifest at the earth.

Levine, R. H.↗

NASA NTRS1979

Microplume model of spatial-yield spectra

An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.

Green, A. E. S.↗

NASA NTRS1979

Optimal estimator model for human spatial orientation

A model is being developed to predict pilot dynamic spatial orientation in response to multisensory stimuli. Motion stimuli are first processed by dynamic models of the visual, vestibular, tactile, and proprioceptive sensors. Central nervous system function is then modeled as a steady-state Kalman filter which blends information from the various sensors to form an estimate of spatial orientation. Where necessary, this linear central estimator has been augmented with nonlinear elements to reflect more accurately some highly nonlinear human response characteristics. Computer implementation of the model has shown agreement with several important qualitative characteristics of human spatial orientation, and it is felt that with further modification and additional experimental data the model can be improved and extended. Possible means are described for extending the model to better represent the active pilot with varying skill and work load levels.

Borah, J.↗

NASA NTRS1979

Spatial quantification of maps or images - Cell size or pixel size implications

The paper discusses spatial quantification of maps or images. Spatial accuracies evaluated by mapping and inventory measures were observed with a range of cell sizes for a 10.36 sq km soil survey segment. The distribution of interboundary distances in a map was evaluated as unique, characterizing information; experimentally observed relationships between accuracy and cell size and interboundary distance distribution parameters and cell size led to a model of the process of spatial quantization. Grid positioning effects were evaluated and were significant only at the level of individual mapping units; two generations of 'universal' process models were derived, implemented, and evaluated.

Wehde, M. E.↗

NASA NTRS1980

The effect of finite turbulence spatial scale on the amplification of turbulence by a contracting stream

The turbulence downstream of a rapid contraction is calculated for the case when the turbulence scale can have the same magnitude as the mean-flow spatial scale. The approach used is based on the formulation of Goldstein (1978) for turbulence downstream of a contraction, with the added assumptions of a parallel mean flow at downstream infinity and turbulence calculated far enough downstream so that the nonuniformity of the mean flow field has decayed, and by treating the inverse contraction ratio as a small parameter. Consideration is given to the large-contraction-ratio and classical rapid-distortion theory limits, and to results at an arbitrary contraction ratio. It is shown that the amplification effect of the contraction is reduced when the spatial scale of the turbulence increases, with the upstream turbulence actually suppressed for a contraction ratio less than five and a turbulence spatial scale greater than three times the transverse dimensions of the downstream channel.

Goldstein, M. E.↗

NASA NTRS1981

Spatial imaging of UV emission from Jupiter and Saturn

Spatial imaging with the IUE is accomplished both by moving one of the apertures in a series of exposures and within the large aperture in a single exposure. The image of the field of view subtended by the large aperture is focussed directly onto the detector camera face at each wavelength; since the spatial resolution of the instrument is 5 to 6 arc sec and the aperture extends 23.0 by 10.3 arc sec, imaging both parallel and perpendicular to dispersion is possible in a single exposure. The correction for the sensitivity variation along the slit at 1216 A is obtained from exposures of diffuse geocoronal H Ly alpha emission. The relative size of the aperture superimposed on the apparent discs of Jupiter and Saturn in typical observation is illustrated. By moving the planet image 10 to 20 arc sec along the major axis of the aperture (which is constrained to point roughly north-south) maps of the discs of these planets are obtained with 6 arc sec spatial resolution.

Clarke, J. T.↗

NASA NTRS1980

HOE/lensless matched spatial filter wavelength-scaling correlator

A scaling correlator optical pattern recognition system is described in which a lensless matched spatial filter (with the second Fourier transform lens and the matched spatial filter recorded on the same plate) is used with a first Fourier transform lens that is also an holographic optical element. The matched spatial filter is recorded at one wavelength and correlation is obtained at a second wavelength. Experimental demonstration and output correlation SNR data are reported, together with a comparison of the system's noise level using conventional optics and holographic elements.

Shen, M.↗

NASA NTRS1981

Spatial and temporal filtering technique for processing lidar photocount data

Shot noise places a practical limit on the spatial and temporal resolution of lidar photocount data. A 2-D signal-processing technique that utilizes spatial and temporal filtering to reduce shot noise and increase resolution is described. The technique is applied to sodium lidar data collected during the fall of 1979 over Urbana, Illinois. Temporal filtering is shown to enhance the spatial resolution of the sodium profiles significantly by reducing shot noise by more than 10 dB. The signal-processing technique is applicable to a wide variety of lidar data.

Gardner, C. S.↗

NASA NTRS1981

Spatial evolution of ocean wave spectra

The spatially evolving deep water synthetic aperture radar (SAR) directional spectra of a mixed ocean wave system are compared with a comprehensive set of surface and aircraft measurements. The evolution of the SAR spectra, at least for ocean wavelengths greater than 80 m, is seen as generally consistent with the auxiliary data set in both time and space. From the spatial evolution of the angular component of the spectra, it is possible to project back to an apparent remote storm source that is also consistent with the storm location via GOES satellite imagery. The data provide compelling evidence that the spatial evolution of SAR ocean wave spectra can be a useful tool in global ocean wave monitoring and forecasting.

Beal, R. C.↗

NASA NTRS1982

Evaluation of spatial filtering on the accuracy of wheat area estimate

A 3 x 3 pixel spatial filter for postclassification was used for wheat classification to evaluate the effects of this procedure on the accuracy of area estimation using LANDSAT digital data obtained from a single pass. Quantitative analyses were carried out in five test sites (approx 40 sq km each) and t tests showed that filtering with threshold values significantly decreased errors of commission and omission. In area estimation filtering improved the overestimate of 4.5% to 2.7% and the root-mean-square error decreased from 126.18 ha to 107.02 ha. Extrapolating the same procedure of automatic classification using spatial filtering for postclassification to the whole study area, the accuracy in area estimate was improved from the overestimate of 10.9% to 9.7%. It is concluded that when single pass LANDSAT data is used for crop identification and area estimation the postclassification procedure using a spatial filter provides a more accurate area estimate by reducing classification errors.

Dejesusparada, N.↗

NASA NTRS1982

Free-streaming radiation in cosmological models with spatial curvature

The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.

Wilson, M. L.↗

NASA NTRS1981

Land cover classification accuracy as a function of sensor spatial resolution

The benefits obtained from sensor systems for monitoring earth resources will depend on the application and interpretation methods used. A frequently used analysis method is supervised per-pixel multispectral classification with a typical application being land cover classification. An investigation is conducted to evaluate the effect of spatial resolution on the ability to classify land cover types with per-pixel digital image classification techniques. Attention is also given to the documentation of changes in scene noise and the percentage of boundary pixels as a function of spatial resolution, in order to improve the understanding of the interrelationship between classification accuracy and spatial resolution. It is found that scene noise varies considerably between land cover categories. Changes in scene noise with coarsening resolution occur at different rates for different categories.

Markham, B. L.↗

NASA NTRS1982

Effects of spatial resolution

Studies of the effects of spatial resolution on extraction of geologic information are woefully lacking but spatial resolution effects can be examined as they influence two general categories: detection of spatial features per se; and the effects of IFOV on the definition of spectral signatures and on general mapping abilities.

Abrams, M.↗

NASA NTRS1982

Spatial and spectral resolution necessary for remotely sensed vegetation studies

An outline is presented of the required spatial and spectral resolution needed for accurate vegetation discrimination and mapping studies as well as for determination of state of health (i.e., detection of stress symptoms) of actively growing vegetation. Good success was achieved in vegetation discrimination and mapping of a heterogeneous forest cover in the ridge and valley portion of the Appalachians using multispectral data acquired with a spatial resolution of 15 m (IFOV). A sensor system delivering 10 to 15 m spatial resolution is needed for both vegetation mapping and detection of stress symptoms. Based on the vegetation discrimination and mapping exercises conducted at the Lost River site, accurate products (vegetation maps) are produced using broad-band spectral data ranging from the .500 to 2.500 micron portion of the spectrum. In order of decreasing utility for vegetation discrimination, the four most valuable TM simulator VNIR bands are: 6 (1.55 to 1.75 microns), 3 (0.63 to 0.69 microns), 5 (1.00 to 1.30 microns) and 4 (0.76 to 0.90 microns).

Rock, B. N.↗

NASA NTRS1983

Crustal geomagnetic field - Two-dimensional intermediate-wavelength spatial power spectra

Two-dimensional Fourier spatial power spectra of equivalent magnetization values are presented for a region that includes a large portion of the western United States. The magnetization values were determined by inversion of POGO satellite data, assuming a magnetic crust 40 km thick, and were located on an 11 x 10 array with 300 km grid spacing. The spectra appear to be in good agreement with values of the crustal geomagnetic field spatial power spectra given by McLeod and Coleman (1980) and with the crustal field model given by Serson and Hannaford (1957). The spectra show evidence of noise at low frequencies in the direction along the satellite orbital track (N-S). indicating that for this particular data set additional filtering would probably be desirable. These findings illustrate the value of two-dimensional spatial power spectra both for describing the geomagnetic field statistically and as a guide for diagnosing possible noise sources.

Mcleod, M. G.↗

NASA NTRS1984

Observed Spatial Properties of the Solar Eigenfunctions and the Implications for the Existence of Resolved Multiplets

Solar oscillations are manifested in the solar atmosphere as spatial and temporal perturbations in the local thermodynamical and mechanical properties. When measuring the solar radius/diameter, these perturbations enter the observation through changes in the radiative source function and opacity at the extreme limb. When compared to the disk center, the observable portion of these perturbations is changed in spatial character by projection effects and oblique optical depth geometry. The time varying solar radius signal at SCLERA (Santa Catalina Laboratory for Experimental Relativity) is produced by an edge definition sensitive to the resultant changes in the spatial shape of the limb intensity profile. An attempt is made to further determine the shape and properties of the limb signals which display global solar oscillations.

Caudell, T. P.↗