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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Anvil Clouds of Tropical Mesoscale Convective Systems in Monsoon Regions

The anvil clouds of tropical mesoscale convective systems (MCSs) in West Africa, the Maritime Continent and the Bay of Bengal have been examined with TRMM and CloudSat satellite data and ARM ground-based radar observations. The anvils spreading out from the precipitating cores of MCSs are subdivided into thick, medium and thin portions. The thick portions of anvils show distinct differences from one climatological regime to another. In their upper portions, the thick anvils of West Africa MCSs have a broad, flat histogram of reflectivity, and a maximum of reflectivity in their lower portions. The reflectivity histogram of the Bay of Bengal thick anvils has a sharply peaked distribution of reflectivity at all altitudes with modal values that increase monotonically downward. The reflectivity histogram of the Maritime Continent thick anvils is intermediate between that of the West Africa and Bay of Bengal anvils, consistent with the fact this region comprises a mix of land and ocean influences. It is suggested that the difference between the statistics of the continental and oceanic anvils is related to some combination of two factors: (1) the West African anvils tend to be closely tied to the convective regions of MCSs while the oceanic anvils are more likely to be extending outward from large stratiform precipitation areas of MCSs, and (2) the West African MCSs result from greater buoyancy, so that the convective cells are more likely to produce graupel particles and detrain them into anvils

Cetrone, J.↗
NASA NTRS2015

Damage Proxy Map from Interferometric Synthetic Aperture Radar Coherence

A method, apparatus, and article of manufacture provide the ability to generate a damage proxy map. A master coherence map and a slave coherence map, for an area prior and subsequent to (including) a damage event are obtained. The slave coherence map is registered to the master coherence map. Pixel values of the slave coherence map are modified using histogram matching to provide a first histogram of the master coherence map that exactly matches a second histogram of the slave coherence map. A coherence difference between the slave coherence map and the master coherence map is computed to produce a damage proxy map. The damage proxy map is displayed with the coherence difference displayed in a visually distinguishable manner.

Yun, Sang-Ho↗
NASA NTRS2018

Magnetospheric Multiscale Observations of Turbulent Magnetic and Electron Velocity Fluctuations in Earth's Magnetosheath Downstream of a Quasi-Parallel Bow Shock

We present statistical single-spacecraft observations of magnetic and electron velocity fluctuations in Earth's magnetosheath, likely in the vicinity of the magnetopause, downstream of a bow shock immersed in quasi-parallel interplanetary magnetic field conditions, a situation conducive to plasma turbulence in the downstream flow. These fluctuations exhibit scale-dependent behavior, wherein histograms of their Partial Variance of Increments (PVIB or PVIV(sub e)) demonstrate highly non-Gaussian forms at small scales and are reasonably well-described by kappa distributions, albeit with fitted values of the kappa parameter only slightly larger than 1.5, exemplifying their power law nature at large values of PVI. At larger scales, the PVI histograms lose their non-Gaussian nature and are well described by both Gaussian and kappa distributions with large values of the kappa parameter. The PVI histograms furthermore exhibit kurtosis that increases with decreasing scale, a characteristic that is much more prominent in the magnetic fluctuations than in the electron velocity fluctuations. This feature that is not yet explained. In both cases, the results are characteristic of turbulent intermittency.

Pollock, C. J.↗
NASA NTRS2021

Probabilistic Processing of Asynchronous Geiger-Mode Avalanche Photodiode Arrays for Background Rate Measurements

A system-level performance evaluation of Geiger-mode avalanche photodiode (GmAPD) arrays requires accurate measurement and prediction of the background rate of the device due to dark counts and other spurious detection events. Since a GmAPD detector reports only a binary value and timestamp associated with an avalanche event, dark count rates are typically measured by averaging thousands of frames to support a statistically significant measurement. For both synchronous and asynchronous detector, the Poisson distributed background rates are referenced to the time each pixel is armed. Unlike for synchronous GmAPD imagers where all the pixels are armed to an array-wide arm signal, an asynchronous pixel operates independently from its neighboring pixels; requiring the background rates to be calculated using an interarrival histogram. For both types of imagers, the background rate is typically evaluated by fitting an exponential distribution to a fixed window within a measured histogram of time intervals between detection events However, if the statistics of the background rate are insufficient – whether that is due to low population sizes, saturation, or a large dynamic range of population size across the array, the pixel, or array-wide, performance metrics may report results with varying accuracy. This paper reports on an implementation of an algorithm that evaluates GmAPD background rates based on statistical metrics rather than fixed windows. The algorithm functions by determining the appropriate integration window within the interarrival time histogram based on a per-pixel count rate set by a predetermined tolerable measurement error. The implementation of the algorithm allows us to characterize GmAPD arrays with orders of magnitude spread in background rates across the detector using common statistical parameters.

Mumolo, J.↗
NASA NTRS1971

Digital tape unit test facility software

Two computer programs are described which are used for the collection and analysis of data from the digital tape unit test facility (DTUTF). The data are the recorded results of skew tests made on magnetic digital tapes which are used on computers as input/output media. The results of each tape test are keypunched onto an 80 column computer card. The format of the card is checked and the card image is stored on a master summary tape via the DTUTF card checking and tape updating system. The master summary tape containing the results of all the tape tests is then used for analysis as input to the DTUTF histogram generating system which produces a histogram of skew vs. date for selected data, followed by some statistical analysis of the data.

Jackson, J. T.↗
NASA NTRS1972

Application of an approach and landing system model to the space shuttle orbiter vehicle

An analytic model and procedure are described which can be used to estimate probability distributions of touchdown conditions, without utilizing a Monte Carlo simulation. Example applications are presented, including one-step and two-step flare strategies for the space shuttle orbiter. The computed probability distributions for the two-step flare are compared with the corresponding histograms from an independent Monte Carlo simulation of the same situation. The computed distributions are very good fits to the Monte-Carlo-generated histograms for pertinent longitudinal and lateral variables at three points (including touchdown) along the vehicle's final approach trajectory. The model, thus verified, has more inherent power for assessing the effects of system element changes than conventional Monte Carlo techniques.

Johnson, W. A.↗
NASA NTRS1973

Further results on cooling mechanisms for soft X-ray flares

Analysis of data from the soft X-ray proportional counter spectrometer on OSO-4 has been continued along the lines of earlier work. It was noticed that the time profiles of X-ray counts from the OSO-4 instrument's 1 to 3 Angstrom detectors for two events showed a very rapid initial decay after maximum, followed by a much more slowly falling section. At least in the case of the larger of the two events, the change of slope seems quite definitely to be discontinuous. Temperatures and emission measures for both flares have been derived, by fitting an emission function to eight-channel count histograms which form the output of the 1 to 3 Angstrom detectors, analyzed into eight energy intervals by pulse-height analysis. The computer program is described. It employs temperature and continuum emission measures in the Culhane-Acton formula and the flux in the 6.7 KeV iron-line feature as free parameters, adjusting them by small amounts in successive iterations until the original historgram is approximately reproduced. A chi-squared is used to examine the agreement between histograms and terminates the iteration accordingly. Account is taken of the proportional counters' energy resolution in the fitting process.

Craig, I. J. D.↗
NASA NTRS1975

Gray-level transformations for interactive image enhancement

A gray-level transformation method suitable for interactive image enhancement was presented. It is shown that the well-known histogram equalization approach is a special case of this method. A technique for improving the uniformity of a histogram is also developed. Experimental results which illustrate the capabilities of both algorithms are described. Two proposals for implementing gray-level transformations in a real-time interactive image enhancement system are also presented.

Fittes, B. A.↗
NASA NTRS1976

LACIE performance predictor final operational capability program description, volume 2

Given the swath table files, the segment set for one country and cloud cover data, the SAGE program determines how many times and under what conditions each segment is accessed by satellites. The program writes a record for each segment on a data file which contains the pertinent acquisition data. The weather data file can also be generated from a NASA supplied tape. The Segment Acquisition Selector Program (SACS) selects data from the segment reference file based upon data input manually and from a crop window file. It writes the extracted data to a data acquisition file and prints two summary reports. The POUT program reads from associated LACIE files and produces printed reports. The major types of reports that can be produced are: (1) Substrate Reference Data Reports, (2) Population Mean, Standard Deviation and Histogram Reports, (3) Histograms of Monte Carlo Statistics Reports, and (4) Frequency of Sample Segment Acquisitions Reports.

Source record↗
NASA NTRS1976

Electric field statistics for close lightning return strokes near Gainesville, Florida

The salient properties of the electric field intensity from first and subsequent lightning return strokes in the 0-25 km distance range near Gainesville, Fla., are presented, including electric field wave shape versus distance, initial peak rise time versus distance, rise time histograms, initial peak magnitude versus distance, normalized (to 100 km) initial peak magnitude histograms, normalized initial peak magnitude versus rise time, ramp starting time versus distance, and field at 170 microsec versus distance. The mean normalized initial peak field for first return strokes was 9.9 V/m and for subsequent strokes, 5.7 V/m. The maximum measured values of normalized initial peak field were about 30 V/m. The largest field recorded at 170 microsec was about 25 kV/m generated by a first stroke within 0.5 km. Return strokes were found to lower a typical charge of the order of 1 C in 170 microsec.

Tiller, J. A.↗
NASA NTRS1977

Characteristics of random inlet pressure fluctuations during flights of F-111A airplane

Compressor face dynamic total pressures from four F-111 flights were analyzed. Statistics of the nonstationary data were investigated by analyzing the data in a quasi-stationary manner. Changes in the character of the dynamic signal are investigated as functions of flight conditions, time in flight, and location at the compressor face. The results, which are presented in the form of rms values, histograms, and power spectrum plots, show that the shape of the power spectra remains relatively flat while the histograms have an approximate normal distribution.

Costakis, W. G.↗
NASA NTRS1977

Estimated probability density functions for the times between flashes in the storms of 12 September 1975, 26 August 1975, and 13 July 1976

A report is given to supplement the progress report of June 17, 1977. In that progress report gamma, lognormal, and Rayleigh probability density functions were fitted to the times between lightning flashes in the storms of 9/12/75, 8/26/75, and 7/13/76 by the maximum likelihood method. The goodness of fit is checked by the Kolmogoroff-Smirnoff test. Plots of the estimated densities along with normalized histograms are included to provide a visual check on the goodness of fit. The lognormal densities are the most peaked and have the highest tails. This results in the best fit to the normalized histogram in most cases. The Rayleigh densities have too broad and rounded peaks to give good fits. In addition, they have the lowest tails. The gamma densities fall inbetween and give the best fit in a few cases.

Tretter, S. A.↗
NASA NTRS1975

Gray-level transformations for interactive image enhancement.

A gray-level transformation method suitable for interactive image enhancement is presented. It is shown that the well-known histogram equalization technique is a special case of this method. Experimental results which establish the superiority of the procedure over histogram equalization are also described.

Gonzalez, R. C.↗
NASA NTRS1976

Ages of highland rocks - The chronology of lunar basin formation revisited

The Ar-39-Ar-40 age studies are presented for thirteen Apollo 16 and 17 highland rocks. The plateau ages range from 3.63 to 4.23 G.y. for ten of the samples which give plateaus. For three of the samples, a Ar-39-Ar-40 age is not obtainable because there is no plateau in the temperature release patterns. The ages of all Ar-39-Ar-40 lunar highland rocks are summarized in histograms for Apollo 16 and 17. The histograms show a preponderance of ages in the 3.95 plus or minus 0.05 G.y. interval with a fair number of ages well in excess of 4.0 G.y. up to 4.3 G.y. The ages of the highland rocks indicate a more or less continuous bombardment of the lunar surface during the first 600 m.y. with the major ring basins being formed randomly during this period and not all in a relatively short interval at 3.9-4.0 G.y. ago.

Schaeffer, O. A.↗
NASA NTRS1977

Energy spectra of cosmic ray nuclei - Z of 4 to 26 and E of 0.3 to 2 GeV/amu

The differential kinetic-energy spectra of cosmic-ray nuclei in the charge range from 4 to 28 are determined using data obtained from a high-altitude balloonborne detector. The data are derived from the response of an acrylic plastic Cerenkov counter and cover the kinetic-energy range from 400 to 2100 MeV/amu. A Cerenkov pulse-height histogram is obtained for each charge, and the kinetic-energy spectra are derived by means of a formal mathematical deconvolution of these histograms. Results of the deconvolution calculation extrapolated to the top of the atmosphere are presented for the most abundant nuclei; it is found that the spectra are not amenable to representation by spectral indices, so the relative spectra of the different elements are compared by evaluating the charge ratios as a function of energy. The results show that secondary/primary ratios decrease with increasing energy, while primary/primary ratios are constant for Z of 6 to 10 and 14 to 26 but vary for Z of 10 to 14. It is concluded that the data seem to indicate more than one cosmic-ray source region.

Maehl, R. C.↗
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.↗