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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Laser velocimeter measurements in a large transonic wind tunnel

A two-component fringe type laser velocimeter operated in the backscatter mode was used to measure the free-stream velocity in an undisturbed flow field in a wind-tunnel test section from Mach 0.2 to Mach 1.0 and to measure the velocity along the stagnating streamline of a hemisphere model from Mach 0.2 to Mach 0.8. Burst signals from the laser velocimeter were processed by high-speed burst counters, and histograms of the number of occurrences of a particular counter output were collected by means of a pulse height analyzer. Arithmetic means of the histograms were calculated, and the results were compared with predicted local gas velocities with allowance for the lag of the scattering particles with respect to the gas flow. The free-stream measurements were accurate to within 2% of the calibration measurements. The stagnation streamline measurements show trends similar to theoretical predictions.

Meyers, J. F.↗
NASA NTRS1978

Digital enhancement of computerized axial tomograms

A systematic evaluation was conducted of certain digital image enhancement techniques performed in image space. Three types of images were used, computer generated phantoms, tomograms of a synthetic phantom, and axial tomograms of human anatomy containing images of lesions, artificially introduced into the tomograms. Several types of smoothing, sharpening, and histogram modification were explored. It was concluded that the most useful enhancement techniques are a selective smoothing of singular picture elements, combined with contrast manipulation. The most useful tool in applying these techniques is the gray-scale histogram.

Roberts, E., Jr.↗
NASA NTRS1978

Additional evidence consistent with solar cycle variations in the solar wind

Analyses of solar-wind observations from mid-1964 through 1973 confirm the earlier results reported by Intriligator (1974) that there were statistically significant variations in the solar wind in 1968 and 1969, years of solar maximum. These variations were in phase with the solar cycle and consistent with a solar-cycle variation in the solar wind. High-speed stream parameters show that the number of high-speed streams in the solar wind in 1968 and 1969 and the total duration (in days) of high-speed streams in 1968 were considerably more than the predicted yearly average, and in 1965 and 1972 considerably less. Histograms of solar-wind speed from 1964 through 1973 indicate that in 1968 there was the highest percentage of elevated solar-wind speeds, and in 1965 and 1972 the lowest. Studies by others confirm these results, although their authors did not indicate this fact. The duration of the streams and the histograms for 1973 may imply a shifting in the primary stream source.

Intriligator, D. S.↗
NASA NTRS1976

Large Area Crop Inventory Experiment (LACIE). Detection of episodic phenomena on LANDSAT imagery

The author has identified the following significant results. Episodic phenomena such as rainfall shortly before data pass, thin translucent clouds, cloud shadows, and aircraft condensation trails and their shadows are responsible for changes in the spectral reflectivities of some surfaces. These changes are readily detected on LANDSAT full-frame imagery. Histograms of selected areas in Kansas show a distinct decrease in mean radiance values, but also, an increase in scene contrast, in areas where recent rains had occurred. Histograms from a few individual fields indicate that the mean radiance values for winter wheat followed a different trend after a rainfall than alfalfa or grasses.

Chesnutwood, C. M.↗
NASA NTRS1977

A fast routine for computing

A routine for calculating multidimensional histograms of multivariate data using a combination table look up and search procedure is described. The software was originally developed to computer four-dimensional histograms from LANDSAT multispectral imagery, but the concept can be used on other types of data and the program can be modified for the desired type of output information.

Jayroe, R. R., Jr.↗
NASA NTRS1978

Digital enhancement of computerized axial tomograms

A systematic evaluation has been conducted of certain digital image enhancement techniques performed in image space. Three types of images have been used, computer generated phantoms, tomograms of a synthetic phantom, and axial tomograms of human anatomy containing images of lesions, artificially introduced into the tomograms. Several types of smoothing, sharpening, and histogram modification have been explored. It has been concluded that the most useful enhancement techniques are a selective smoothing of singular picture elements, combined with contrast manipulation. The most useful tool in applying these techniques is the gray-scale histogram.

Roberts, E., Jr.↗
NASA NTRS1980

Use of the transect method in satellite survey missions with application to the infrared astronomical satellite /IRAS/

The coverage of the celestial sphere or the surface of the earth with a narrow-field instrument onboard a satellite can be described by a set of swaths on the sphere. A transect is a curve on this sphere constructed to sample the coverage. At each point on the transect the number of times that the field-of-view of the instrument has passed over the point is recorded. This information is conveniently displayed as an integer-valued histogram over the length of the transect. The effectiveness of the transect method for a particular observing plan and the best placement of the transects depends upon the structure of the set of observations. Survey missions are usually characterized by a somewhat parallel alignment of the instrument swaths. Using autocorrelation and cross-correlation functions among the histograms the structure of a survey has been analyzed into two components, and each is illustrated by a simple mathematical model. The complex, all-sky survey to be performed by the Infrared Astronomical Satellite (IRAS) is synthesized in some detail utilizing the objectives and constraints of that mission. It is seen that this survey possesses the components predicted by the simple models and this information is useful in characterizing the properties of the IRAS survey and the placement of the transects as a function of celestial latitude and certain structural properties of the coverage.

Mclaughlin, W. I.↗
NASA NTRS1980

Determination of optimum voltages of ion focusing devices using computer techniques

Electric potentials for two dimensional cross sections of ion focusing devices used in a mass spectrometer are calculated via a series of computer programs designed to compute potentials between areas of fixed voltages. Ion trajectories within these devices may be determined by computer and a histogram obtained which plots ion density against ion position along a plate of the focusing device. For each lens system, a plate voltage may be changed, the electric potentials recalculated, and a new histogram calculated in order to determine if the new voltage configuration has increased the device's efficiency. This process may be repeated until the optimum voltage values have been found for maximum particle transmission in each focusing device.

Eckstein, B. A.↗
NASA NTRS1980

Catalog of sea state and wind speed in the South Atlantic Bight

The GEOS 3 significant waveheight and ground wind speed estimation algorithms are derived and then applied to all GEOS 3 data in the South Atlantic Bight. The investigation area is divided into five geographical sectors and significant waveheight and wind speed histograms are presented in each sector by month and by season. In the discussion of the histograms, definite seasonal trends are identified and examined.

Mcmillan, J. D.↗
NASA NTRS1982

NOSS-SCAT wind direction alias removal

The use of automated algorithms for removing aliases in NOSS-SCAT data is reported. The algorithms used for alias removal consist of histogram analysis, local averaging and curve fitting. The histogram analysis is used to determine the degree of homogeneity of the wind field defined by the largest probability alias vector at each grid point. The alias directions are compared with the preferred direction at each grid location and one of the multiple aliases is chosen as the true direction.

Shanmugan, K. S.↗
NASA NTRS1982

Automatic classification of clouds on Meteosat imagery - Application to high-level clouds

A statistical classification method based on clustering on three-dimensional histograms is applied to the three channels of the Meteosat imagery. The results of this classification are studied for different cloud cover cases over tropical regions. For high-level cloud classes, it is shown that the bidimensional IR-water vapor histogram allows one to deduce the cloud top temperature even for semi-transparent clouds.

Desbois, M.↗
NASA NTRS1983

Microprocessor-Based Neural-Pulse-Wave Analyzer

Microprocessor-based system analyzes amplitudes and rise times of neural waveforms. Displaying histograms of measured parameters helps researchers determine how many nerves contribute to signal and specify waveform characteristics of each. Results are improved noise rejection, full or partial separation of overlapping peaks, and isolation and identification of related peaks in different histograms. 2

Kojima, G. K.↗
NASA NTRS1982

Subkilometer Martian volcanoes - Properties and possible terrestrial analogs

Kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of Mars. Based on examination of more than 12,000 high resolution Viking Orbiter images, most of these very small cones are located in parts of Eastern Acidalia and Utopia-Isidis-Elysium Planitia. Measurements of base and pit diameter for some 2000 well-resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater/cone diameter ratios. This suggests that the small cones had a similar origin with only minor variations in local conditions. The Acidalia cones are generally larger, more widely distributed, and occur on a greater variety of terrains than those in Utopia-Isidis-Elysium. Based on morphology, distribution, and the crater/cone ratio histograms, the smallest Martian cones may be similar to Icelandic pseudocraters. Somewhat larger, steeper cones with smaller crater/cone ratios which also occur in Eastern Acidalia may be analogs of terrestrial cinder cones.

Frey, H.↗
NASA NTRS1983

The thermoluminescence carrier in the Dhajala chondrite

It is pointed out that the type 3 (unequilibrated) ordinary chondrites provide a major source of information on the early solar system. However, the interpretation of the data is difficult because all but a few display signs of metamorphic alteration. The present investigation is concerned with the thermoluminescence (TL) sensitivity measurements on 58 chondrules separated from the Dhajala meteorites. The data were discussed briefly by Sparks and Sears (1982). In the current investigation particular attention is given to the constraints placed by these data on the mechanism by which metamorphism is related to TL sensitivity. Dhajala-normalized TL sensitivity of the separated chondrules is plotted against chondrule mass, and a histogram of the CaO contents of 15 chondrules is presented. Histograms showing the TL sensitivity of chondrules separated from the Dhajala meteorite are also provided.

Sparks, M. H.↗
NASA NTRS1983

Chemical and physical studies of type 3 chondrites. II Thermoluminescence of sixteen type 3 ordinary chondrites and relationships with oxygen isotopes

Thermoluminescence (TL) sensitivity values for sixteen type 3 ordinary chondrites, fourteen of them from Antarctica, have been measured. The values obtained (normalized to the TL sensitivity of the Dhajala meteorite) range from 1.6 (Allan Hills A77216) to 0.010 (Allan Hills A77176), and include two (Reckling Peak A80207 and Allan Hills A77176) that are particularly low. They fill a hiatus in the TL distribution that previously existed between St. Mary's County and Bishunpur, the latter being a meteorite with one of the lowest TL sensitivities known. The histogram of TL sensitivity values now shows a single distribution with higher values preferred; it resembles the histogram for L chondrites occupying the petrologic types 3, 4, 5, and 6. There is a tendency for the TL sensitivity of meteorites to decrease as delta O-18 increases. Theoretically, it is possible that the range of delta O-18 values observed may reflect progressive loss of O in the form of CO at very low temperatures, but very restrictive physical conditions and a complex history seem to be required.

Sears, D. W. G.↗
NASA NTRS1986

Diurnal variation of outgoing longwave radiation in the tropics

The diurnal harmonic in longwave emission in the tropical belt (30 deg N-30 deg S) is estimated from nine years of NOAA polar-orbiting satellite data. The results are compared successfully with Nimbus-7 ERB scanner data and with GOES-West geosynchronous satellite data. An interesting and consistent diurnal variation in longwave emission is found over the regions of intense oceanic convection, such as the ITCZ and SPCZ regions, with a peak-to-peak variation of 6-8 W/sq m and a maximum in the morning (0600-1200 LST). Histogram analysis indicates that this variation is associated with a diurnal variation in convective cloud (about 400 mb). Over regions of very intense convection, a diurnal variation of very high clouds (above 100 mb), which is out of phase with the variations at lower levels in the atmosphere, reduces the magnitude of the diurnal harmonic in longwave emission. It is interesting that histograms based on data averaged over 8-km and 250-km boxes give the same qualitative information about cloud and emission variability.

Hartmann, D. L.↗
NASA NTRS1986

Analysis of memory use for improved design and compile-time allocation of local memory

Trace analysis techniques are used to study memory referencing behavior for the purpose of designing local memories and determining how to allocate them for data and instructions. In an attempt to assess the inherent behavior of the source code, the trace analysis system described here reduced the effects of the compiler and host architecture on the trace by using a technical called flattening. The variables in the trace, their associated single-assignment values, and references are histogrammed on the basis of various parameters describing memory referencing behavior. Bounds are developed specifying the amount of memory space required to store all live values in a particular histogram class. The reduction achieved in main memory traffic by allocating local memory is specified for each class.

Mcniven, Geoffrey D.↗
NASA NTRS1986

Color enhancement of highly correlated images. I - Decorrelation and HSI contrast stretches

Conventional enhancements for the color display of multispectral images are based on independent contrast modifications or 'stretches' of three input images. This approach is not effective if the image channels are highly correlated or if the image histograms are strongly bimodal or more complex. Any of several procedures that tend to 'stretch' color saturation while leaving hue unchanged may better utilize the full range of colors for the display of image information. Two conceptually different enhancements are discussed: the 'decorrelation stretch', based on principal-component (PC) analysis, and the 'stretch' of 'hue' - 'saturation' - intensity (HSI) transformed data. The PC transformation in scene-dependent, but the HSI transformation is invariant. Examples of images enhanced by conventional linear stretches, decorrelation stretch, and by stretches of HSI transformed data are compared. Schematic variation diagrams or two- and three-dimensional histograms are used to illustrate the 'decorrelation stretch' method and the effect of the different enhancements.

Gillespie, Alan R.↗