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At least 541 records · Page 30

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NASA NTRS1977

Interactions of satellite-speed helium atoms with satellite surfaces. 3: Drag coefficients from spatial and energy distributions of reflected helium atoms

Spatial and energy distributions of helium atoms scattered from an anodized 1235-0 aluminum surface as well as the tangential and normal momentum accommodation coefficients calculated from these distributions are reported. A procedure for calculating drag coefficients from measured values of spatial and energy distributions is given. The drag coefficient calculated for a 6061 T-6 aluminum sphere is included.

Sharma, P. K.↗

NASA NTRS1978

A parametric multiclass Bayes error estimator for the multispectral scanner spatial model performance evaluation

The author has identified the following significant results. The probability of correct classification of various populations in data was defined as the primary performance index. The multispectral data being of multiclass nature as well, required a Bayes error estimation procedure that was dependent on a set of class statistics alone. The classification error was expressed in terms of an N dimensional integral, where N was the dimensionality of the feature space. The multispectral scanner spatial model was represented by a linear shift, invariant multiple, port system where the N spectral bands comprised the input processes. The scanner characteristic function, the relationship governing the transformation of the input spatial, and hence, spectral correlation matrices through the systems, was developed.

Mobasseri, B. G.↗

NASA NTRS1977

Silicon vidicon imaging of Jupiter - 4100- to 8300-A absolute reflectivities and limb darkening of spatially resolved regions

Jupiter was observed in six continuum wavelength channels in the region 4100-8300 A, using a silicon vidicon imaging photometer. Spectral reflectivities and high spatial resolution limb-darkening curves for several belts and zones have been extracted from the data. Simple model fits to the data yield information regarding spectral and spatial variations in single-scattering albedos and shape of particle single-scattering phase functions. Belts appear to be more backscattering than zones, particularly in the blue. The data are in moderate agreement with limb-darkening predicted by models derived from the center-to-limb variation in equivalent width of the H2 4-0 S(1) quadrupole line (Cochran, 1976) in the South Tropical Zone, but strongly disagree with the results of such models for the North Equatorial Belt.

Diner, D. J.↗

NASA NTRS1978

Some influences of touch and pressure cues on human spatial orientation

In order to evaluate the influences of touch and pressure cues on human spatial orientation, blindfolded subjects were exposed to 30 rmp rotation about the Z-axis of their bodies while the axis was horizontal or near horizontal. It was found that the manipulation of pressure patterns to which the subjects are exposed significantly influences apparent orientation. When provided with visual information about actual orientation the subjects will eliminate the postural illusions created by pressure-cue patterns. The localization of sounds is dependent of the apparent orientation and the actual pattern of auditory stimulation. The study provides a basis for investigating: (1) the postural illusions experienced by astronauts in orbital flight and subjects in the free-fall phase of parabolic flight, and (2) the spatial-constancy mechanisms distinguishing changes in sensory afflux conditioned by a subject's movements in relation to the environment, and those conditioned by movements of the environment.

Lackner, J. R.↗

NASA NTRS1978

Numerical method for solution of systems of non-stationary spatially one-dimensional nonlinear differential equations

A computational scheme and a standard program is proposed for solving systems of nonstationary spatially one-dimensional nonlinear differential equations using Newton's method. The proposed scheme is universal in its applicability and its reduces to a minimum the work of programming. The program is written in the FORTRAN language and can be used without change on electronic computers of type YeS and BESM-6. The standard program described permits the identification of nonstationary (or stationary) solutions to systems of spatially one-dimensional nonlinear (or linear) partial differential equations. The proposed method may be used to solve a series of geophysical problems which take chemical reactions, diffusion, and heat conductivity into account, to evaluate nonstationary thermal fields in two-dimensional structures when in one of the geometrical directions it can take a small number of discrete levels, and to solve problems in nonstationary gas dynamics.

Morozov, S. K.↗

NASA NTRS1978

Spatial land-use inventory, modeling, and projection/Denver metropolitan area, with inputs from existing maps, airphotos, and LANDSAT imagery

A landscape model was constructed with 34 land-use, physiographic, socioeconomic, and transportation maps. A simple Markov land-use trend model was constructed from observed rates of change and nonchange from photointerpreted 1963 and 1970 airphotos. Seven multivariate land-use projection models predicting 1970 spatial land-use changes achieved accuracies from 42 to 57 percent. A final modeling strategy was designed, which combines both Markov trend and multivariate spatial projection processes. Landsat-1 image preprocessing included geometric rectification/resampling, spectral-band, and band/insolation ratioing operations. A new, systematic grid-sampled point training-set approach proved to be useful when tested on the four orginal MSS bands, ten image bands and ratios, and all 48 image and map variables (less land use). Ten variable accuracy was raised over 15 percentage points from 38.4 to 53.9 percent, with the use of the 31 ancillary variables. A land-use classification map was produced with an optimal ten-channel subset of four image bands and six ancillary map variables. Point-by-point verification of 331,776 points against a 1972/1973 U.S. Geological Survey (UGSG) land-use map prepared with airphotos and the same classification scheme showed average first-, second-, and third-order accuracies of 76.3, 58.4, and 33.0 percent, respectively.

Tom, C.↗

NASA NTRS1979

Evaluation of the spatial and temporal measurement requirements of remote sensors for monitoring regional air pollution episodes

The spatial and temporal measurement requirements of satellite sensors for monitoring regional air pollution episodes were evaluated. Use was made of two sets of data from the Sulfate Regional Experiment (SURE), which provided the first ground-based aerosol measurements from a regional-scale station network. The sulfate data were analyzed for two air pollution episode cases. The results of the analysis indicate that the key considerations required for episode mapping from satellite sensors are the following: (1) detection of sulfate levels exceeding 20 micron-g/cu m; (2) capability to view a broad area (of the order of 1500 km swath) because of regional extent of pollution episodes; (3) spatial resolution sufficient to detect variations in sulfate levels of greater than 10 micron-g/cu m over distances of the order of 50 to 75 km; (4) repeat coverage at least on a daily basis; and (5) satellite observations during the mid to late morning local time, when the sulfate levels have begun to increase after the early morning minimum levels, and convective-type cloud cover has not yet increased to the amount reached later in the afternoon. Analysis of the satellite imagery shows that convective clouds can obscure haze patterns. Additional parameters based on spectral analysis include wavelength and bandwidth requirements.

Burke, H. H. K.↗

NASA NTRS1979

Spatially resolved reflectivities of Jupiter during the 1976 opposition

Spatially resolved absolute reflectivities of several regions of the Jovian disk in the wavelength region 3000 to 10760 A are presented. Spectra were obtained of the central meridian and limbs of the Equatorial Region, North Equatorial Belt, and North Tropical Zone. Equivalent widths of several CH4 and NH3 bands are measured. The spatial variations of continuum reflectivity and absorption band profiles are shown in various ratio spectra.

Woodman, J. H.↗

NASA NTRS1978

Spatially dominated solar particle events 1972-1976

Low-energy solar-particle data from the APL/JHU experiments on IMP 7 and 8 during 50 solar rotations between September 1972 and May 1976 are examined, and it is found that spatial gradients which are nearly independent of particle rigidity and species dominate the time histories. There are 57 rounded events with gradients on each side, 17 spatially dominated decays of flare-associated temporal events, and 9 broad minima. These events fill about 70% of the total time period, and about 70% are associated with solar-wind streams. The e-folding lengths of the gradients average about 20 deg heliographic longitude, and the rounded events have soft spectra and are helium-rich. These events are consistent with coronal propagation from a central source by a mechanism independent of particle species and energy.

Gold, R. E.↗

NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗

NASA NTRS1979

Gradient and curvature drifts in magnetic fields with arbitrary spatial variation

It is shown that, for a magnetic field of arbitrary spatial variation, a nearly isotropic distribution of charged particles drifts with a velocity given by the usual first-order orbit theory drifts averaged over pitch angle. It is assumed that the near-isotropy brought about by scattering, but conclusions concerning drift are insensitive to the details of the scattering process. It is found that this drift velocity is correct even for arbitrarily large ratios of particle gyroradius to magnetic spatial scale, although this velocity must, like all drift effects, be viewed on a scale larger than a gyroradius. Hence for many astrophysical applications, such as cosmic rays, where anisotropies are small, the usual drift velocities provide a valid approximation to convective motions even if the magnetic field scales are very small.

Isenberg, P. A.↗

NASA NTRS1980

Spatial distribution of XUV emission and density in a loop prominence

The spatial distribution of XUV emission in the 14 August, 1973 loop prominence observed with the NRL spectroheliograph on Skylab is studied. The loop prominence consists of two large loops and is observed in lines from ions with temperatures ranging from 50,000 to 3,000,000 K. The loops seen in low temperature lines such as from He II, Ne VII, Mg VII, Mg VIII, and Si VIII are systematically displaced from loops seen in higher temperature lines such as from Si XII, Fe XV, and Fe XVI. The cross section of the loop, particularly in cooler lines is nearly constant along the loop. For hotter loops in Si XII, Fe XV, and Fe XVI, however, emission at the top of the loop is more intense and extended than that near the footpoints, which makes the loops appear wider at the top. The observed spatial displacement between cooler and hotter loops suggest that the 14 August loop prominence is composed of many magnetic flux tubes, each with its own temperature.

Cheng, C.-C.↗

NASA NTRS1980

Spatial aspects of low- and medium-energy electron degradation in N2

Spatial (radial and longitudinal) yield spectra for electron energy degradation in molecular nitrogen gas for 25-eV to 10-keV incident electrons have been generated by using a Monte Carlo technique. These spatial yield spectra associated with the electron degradation process can be employed to calculate a 'yield' for any inelastic state at any position in the medium. These have been analytically represented in terms of a model containing three simple 'microplumes'. Five-dimensional yield spectra which contain the information about the polar angle of the electron have also been analytically represented within the framework of the microplume model. Aeronomical and radiological applications of our model are discussed.

Singhal, R. F.↗

NASA NTRS1980

Spatial power spectra of the crustal geomagnetic field and core geomagnetic field

Equations providing numerical values of the geomagnetic field spherical harmonic spatial power spectrum as defined by Lowes (1966, 1974) are obtained and this power spectrum is related to various other power spectra. Equations relating the spherical harmonic spatial power spectrum to average great circle power spectra for components of the vector magnetic field in the radial direction, along the great circle track and perpendicular to the first two directions are derived under the assumption that the sources of the field are internal. A statistical model for the crustal and core geomagnetic fields is proposed and used to derive equations for the expected main and crustal spherical harmonic power spectra. The model equations are then compared with observations to determine a scale factor which is then used to obtain an estimate for the core radius and a great circle power spectrum for the field component perpendicular to the great circle and radial directions which are in good agreement with observations. The predicted spherical harmonic power spectrum for the crustal field is found to be consistent with POGO satellite and aircraft data. Other possible models for the crustal and core geomagnetic fields are also briefly considered.

Mcleod, M. G.↗

NASA NTRS1981

Temporal and spatial inconsistencies of time-split finite-difference schemes

The properties of an implicit time-split algorithm, which utilizes locally one dimensional spatial steps, are examined using the two-dimensional heat conduction equation as the test problem. Both temporal and spatial inconsistencies inherent in the scheme are identified. A consistent, implicit splitting approach is developed. The relationship between this method and other time-split implicit schemes is explained, and stability problems encountered with the method in three dimensions are discussed.

Dwoyer, D. L.↗

NASA NTRS1980

The development of a spectral-spatial classifier for earth observational data

Over the last several years a classifier for earth observational image data has been under development intended to achieve improved performance by utilizing spatial characteristics of the data as an adjunct to multispectral properties. The paper provides an overview of the conception, development, evaluation and documentation of this spectral-spatial classifier. The research program leading to this classifier is described, the algorithms of the current implementation called ECHO are outlined, and results on its performance are summarized. These results show improved accuracy, with greater computation efficiency, and only slightly increased operator complexity.

Landgrebe, D. A.↗

NASA NTRS1981

Spatial aspects of electron energy degradation in atomic oxygen

Spatial (radial and longitudinal) yield spectra for electron energy degradation in atomic oxygen have been obtained using a Monte Carlo method for 25 eV to 10 keV incident electrons. Four-dimensional yield spectra have been analytically represented in terms of a model containing three simple microplumes. We find that the scaled spatial yield spectra for O is approximately the same as for N2. This feature provides a basis for inferring yield spectra for any atmosphere gas or mixture of gases.

Singhal, R. P.↗

NASA NTRS1981

Spatially resolved absolute spectrophotometry of Saturn - 3390 to 8080 A

A series of spatially resolved absolute spectrophotometric measurements of Saturn was conducted for the expressed purpose of calibrating the data obtained with the Imaging Photopolarimeter (IPP) on Pioneer 11 during its recent encounter with Saturn. All observations reported were made at the Mt. Wilson 1.5-m telescope, using a 1-m Ebert-Fastie scanning spectrometer. Spatial resolution was 1.92 arcsec. Photometric errors are considered, taking into account the fixed error, the variable error, and the composite error. The results are compared with earlier observations, as well as with synthetic spectra derived from preliminary physical models, giving attention to the equatorial region and the South Temperate Zone.

Bergstralh, J. T.↗