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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Ion extraction from a plasma

An experimental investigation of the physical processes governing ion extraction from a plasma is presented. The screen hole plasma sheath of a multiaperture ion accelerator system is defined by equipotential plots for a variety of accelerator system geometries and operating conditions. A sheath thickness of at least fifteen Debye lengths is shown to be typical. The electron density variation within the sheath satisfies a Maxwell Boltzmann density distribution at an effective electron temperature dependent on the discharge plasma primary to Maxwellian electron density ratio. Plasma ion flow up to and through the sheath is predominately one dimensional and the ions enter the sheath with a modified Bohm velocity. Low values of the screen grid thickness to screen hole diameter ratio give good ion focusing and high extracted ion currents because of the effect of screen webbing on ion focusing.

Aston, G.↗
NASA NTRS1980

On extracting brightness temperature maps from scanning radiometer data

The extraction of brightness temperature maps from scanning radiometer data is described as a typical linear inverse problem. Spatial quantization and parameter estimation is described and is suggested as an advantageous approach to a solution. Since this approach takes into explicit account the multivariate nature of the problem, it permits an accurate determination of the most detailed resolution extractable from the data as well as explicitly defining the possible compromises between accuracy and resolution. To illustrate the usefulness of the method described for algorithm design and accuracy prediction, it was applied to the problem of providing brightness temperature maps during the NOSS flight segment. The most detained possible resolution was determined and a curve which displays the possible compromises between accuracy and resolution was provided.

Argentiero, P.↗
NASA NTRS1982

Supercritical-Fluid Extraction of Oil From Tar Sands

New supercritical solvent mixtures have been laboratory-tested for extraction of oil from tar sands. Mixture is circulated through sand at high pressure and at a temperature above critical point, dissolving organic matter into the compressed gas. Extract is recovered from sand residues. Low-temperature super-critical solvents reduce energy consumption and waste-disposal problems.

Compton, L. E.↗
NASA NTRS1981

Washburn extraction and width of the IUE point spread function

The Washburn Extraction Routine for low dispersion IUE spectra was reviewed. The shape of the point spread function (PSF) in low dispersion spectra is sufficiently well described by a gaussian function. The PSF is in large and small aperture essentially identical and values of sigma are presented. Several advantages of the extraction routine are mentioned.

Deboer, K. S.↗
NASA NTRS1981

Ion extraction from a plasma

The physical processes governing ion extraction from a plasma have been examined experimentally. The screen hole plasma sheath (the transition region wherein significant ion acceleration and complete electron retardation occurs) has been defined by equipotential plots for a variety of ion accelerator system geometries and operating conditions. It was found that the screen hole plasma sheath extends over a large distance, and influences ion and electron trajectories at least 15 Debye lengths within the discharge chamber. The electron density variation within the screen hole plasma sheath satisfied a Maxwell-Boltzmann density distribution at an effective electron temperature dependent on the discharge plasma primary-to-Maxwellian electron density ratio. Plasma ion flow up to and through the sheath was predominantly one-dimensional, and the ions entered the sheath region with a modified Bohm velocity. Low values of the screen grid thickness to screen hole diameter ratio were found to give good ion focusing and high extracted ion currents because of the effect of screen webbing on ion focusing.

Aston, G.↗
NASA NTRS1981

Analysis of soil moisture extraction algorithm using data from aircraft experiments

A soil moisture extraction algorithm is developed using a statistical parameter inversion method. Data sets from two aircraft experiments are utilized for the test. Multifrequency microwave radiometric data surface temperature, and soil moisture information are contained in the data sets. The surface and near surface ( or = 5 cm) soil moisture content can be extracted with accuracy of approximately 5% to 6% for bare fields and fields with grass cover by using L, C, and X band radiometer data. This technique is used for handling large amounts of remote sensing data from space.

Burke, H. H. K.↗
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

A Study of Feature Extraction Using Divergence Analysis of Texture Features

An empirical study of texture analysis for feature extraction and classification of high spatial resolution remotely sensed imagery (10 meters) is presented in terms of specific land cover types. The principal method examined is the use of spatial gray tone dependence (SGTD). The SGTD method reduces the gray levels within a moving window into a two-dimensional spatial gray tone dependence matrix which can be interpreted as a probability matrix of gray tone pairs. Haralick et al (1973) used a number of information theory measures to extract texture features from these matrices, including angular second moment (inertia), correlation, entropy, homogeneity, and energy. The derivation of the SGTD matrix is a function of: (1) the number of gray tones in an image; (2) the angle along which the frequency of SGTD is calculated; (3) the size of the moving window; and (4) the distance between gray tone pairs. The first three parameters were varied and tested on a 10 meter resolution panchromatic image of Maryville, Tennessee using the five SGTD measures. A transformed divergence measure was used to determine the statistical separability between four land cover categories forest, new residential, old residential, and industrial for each variation in texture parameters.

Hallada, W. A.↗
NASA NTRS1983

Supercritical multicomponent solvent coal extraction

The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal.

Corcoran, W. H.↗
NASA NTRS1984

Ion extraction capabilities of two-grid accelerator systems

An experimental investigation into the ion extraction capabilities of two-grid accelerator systems common to electrostatic ion thrusters is described. This work resulted in a large body of experimental data which facilitates the selection of the accelerator system geometries and operating parameters necessary to maximize the extracted ion current. Results suggest that the impingement-limited perveance is not dramatically affected by reductions in screen hole diameter to 0.5 mm. Impingement-limited performance is shown to depend most strongly on grid separation distance, accelerator hole diameter ratio, the discharge-to-total accelerating voltage ratio, and the net-to-total accelerating voltage ratio. Results obtained at small grid separation ratios suggest a new grid operating condition where high beam current per hole levels are achieved at a specified net accelerating voltage. It is shown that this operating condition is realized at an optimum ratio of net-to-total accelerating voltage ratio which is typically quite high. The apparatus developed for this study is also shown to be well suited measuring the electron backstreaming and electrical breakdown characteristics of two-grid accelerator systems.

Rovang, D. C.↗
NASA NTRS1983

On the extraction of atmospheric turbulence parameters from radar backscatter Doppler spectra. Part 1: Theory

A theory is developed for the extraction of r.m.s. velocities of scatterer motions from spectra measured with a Doppler backscatter radar. The effects of finite beam-widths, finite pulse lengths, beam broadening, shear broadening, and the other such spectral contaminants are considered. It is shown that these contaminants can play a major role in determining the measured spectral widths (and, equivalently, the signal fading time), and so must be properly considered if the spectral widths are to be used to extract the r.m.s. motions of the scatterers. It is also shown that these r.m.s. motions can be used to estimate turbulence intensities, in those cases where turbulence is the dominant cause of the scatterer motions.

Hocking, W. K.↗
NASA NTRS1984

Digital processing considerations for extraction of ocean wave image spectra from raw synthetic aperture radar data

The digital processing requirements of several algorithms for extracting the spectrum of a detected synthetic aperture radar (SAR) image from the raw SAR data are described and compared. The most efficient algorithms for image spectrum extraction from raw SAR data appear to be those containing an intermediate image formation step. It is shown that a recently developed compact formulation of the image spectrum in terms of the raw data is computationally inefficient when evaluated directly, in comparison with the classical method where matched-filter image formation is an intermediate result. It is also shown that a proposed indirect procedure for digitally implementing the same compact formulation is somewhat more efficient than the classical matched-filtering approach. However, this indirect procedure includes the image formation process as part of the total algorithm. Indeed, the computational savings afforded by the indirect implementation are identical to those obtained in SAR image formation processing when the matched-filtering algorithm is replaced by the well-known 'dechirp-Fourier transform' technique. Furthermore, corrections to account for slant-to-ground range conversion, spherical earth, etc., are often best implemented in the image domain, making intermediate image formation a valuable processing feature.

Lahaie, I. J.↗
NASA NTRS1984

Ion extraction capabilities of two-grid accelerator systems

An experimental investigation into the ion extraction capabilities of two-grid accelerator systems common to electrostatic ion thrusters is described. A large body of experimental data which facilitates the selection of the accelerator system geometries and operating parameters necessary to maximize the extracted ion current is presented. Results suggest that the impingement-limited perveance is not dramatically affected by reductions in screen hole diameter to 0.5 mm. Impingement-limited performance is shown to depend most strongly on grid separation distance, accelerator hole diameter ratio, the discharge-to-total accelerating voltage ratio, and the net-to-total accelerating voltage ratio. Results obtained at small grid separation ratios suggest a new grid operating condition where high beam current per hole levels are achieved at a specified net accelerating voltage. It is shown that this operating condition is realized at an optimum ratio of net-to-total accelerating voltage ratio which is typically quite high.

Rovang, D. C.↗
NASA NTRS1986

Device for Extracting Flavors and Fragrances

Machine for making coffee and tea in weightless environment may prove even more valuable on Earth as general extraction apparatus. Zero-gravity beverage maker uses piston instead of gravity to move hot water and beverage from one chamber to other and dispense beverage. Machine functions like conventional coffeemaker during part of operating cycle and includes additional features that enable operation not only in zero gravity but also extraction under pressure in presence or absence of gravity.

Chang, F. R.↗
NASA NTRS1987

Methods for extracting aerodynamic accelerations from Orbiter High Resolution Accelerometer Package flight data

This report presents a process for extracting the aerodynamic accelerations of the Shuttle Orbiter Vehicle from the High Resolution Accelerometer Package (HiRAP) flight data during reentry. The methods for obtaining low-level aerodynamic accelerations, principally in the rarefied flow regime, are applied to 10 Orbiter flights. The extraction process is presented using data obtained from Space Transportation System Flight 32 (Mission 61-C) as a typical example. This process involves correcting the HiRAP measurements for the effects of temperature bias and instrument offset from the Orbiter center of gravity, and removing acceleration data during times they are affected by thruster firings. The corrected data are then made continuous and smooth and are further enhanced by refining the temperature bias correction and removing effects of the auxiliary power unit actuation. The resulting data are the current best estimate of the Orbiter aerodynamic accelerations during reentry and will be used for further analyses of the Orbiter aerodynamics and the upper atmosphere characteristics.

Thompson, J. M.↗
NASA NTRS1988

Cartographic feature extraction with integrated SIR-B and Landsat TM images

A digital cartographic multisensor image database of excellent geometry and improved resolution was created by registering SIR-B images to a rectified Landsat TM reference image and applying intensity-hue-saturation enhancement techniques. When evaluated against geodetic control, RMSE(XY) values of approximately + or - 20 m were noted for the composite SIR-B/TM images. The completeness of cartographic features extracted from the composite images exceeded those obtained from separate SIR-B and TM image data sets by approximately 10 and 25 percent, respectively, indicating that the composite images may prove suitable for planimetric mapping at a scale of 1:100,000 or smaller. At present, the most effective method for extracting cartographic information involves digitizing features directly from the image processing display screen.

Welch, R.↗