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All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Elemental abundances of cosmic rays with Z33 as measured on HEAO-3

The Heavy Nuclei Experiment on HEAO-3 uses a combination of ion chambers and a Cerenkov counter. During analysis, each particle is assigned two parameters Z sub c and Z sub l proportion signal is double valued, a unique assignment of particle charge, Z, is not possible in general. Previous work was limited to particles of either high rigidity or low energy, for which a unique charge assignment was possible, although those subsets contain less than 50% of the total number of particles observed. The use of the maximum likelihood technique to determine abundances for the complete data set from approximately 1.5 to approximately 80 GeV/amu is studied.

Newport, B. J.↗
NASA NTRS1985

Elemental abundances of cosmic rays with Z 33 as measured on HEAO-3

The Heavy Nuclei Experiment on (HEAO-3) high energy astronomy observatory 3 uses a combination of ion chambers and a Cerenkov counter. During analysis, each particle is assigned two parameters, Z sub c and Z sub i, proportional to the square roots of the Cerenkov and mean ionization signals respectively. Because the ionization signal is double valued, a unique assignment of particle charge, Z, is not possible in general. Previous work was limited to particles of either high rigidity or low energy, for which a unique charge assignment was possible, although those subsets contain less than 50% of the total number of particles observed. The maximum likelihood technique was used to determine abundances for the complete data set from approx. 1.5 to approx. 80 GeV/amu.

Newport, B. J.↗
NASA NTRS1985

Measurement of interaction cross section of cosmic ray Fe nuclei (E4 GeV/N) with Al target

Although the study of relatvistic heavy ion interaction encumbered by the low intensities of the incident heavy nuclei in cosmic ray experiments, however, one can use a suitable structure of detector to attain a result with a reasonable accuracy. A cross section value of Fe(E 4 GeV/N) with Al is presented. CR-39 was used as detector and Al as target. The cross section value is estimated using maximum likelihood method.

Ren, G. X.↗
NASA NTRS1985

Study of the time-differentiated particle flux density at various distances from EAS axis

The EAS time structure is studied using the enlarged EAS array of the Moscow State University. The time measurements are made using 22 scintillators which form 13 rectanges of 180x190 sq m size covering the entire array area. The array is triggered by a signal of 4-fold coincidences of the pulses from the detectors forming each of the rectangles. The data were obtained during 2200 hours of the array operation in 1984. A total of 816 showers, to which at least 14 of 22 scintillator detectors responded, were selected among all those detected. The coordinates of the EAS axis in the observation plane and the EAS sizes were determined by the maximum likelihood method using a computer on the assumption that the electron LDF is the NKG form. A total of 492 showers in the interval of EAS size Ne = 5x10 to the 6th power - 2x10 to the 8th power (N bar e = 1.7x 10 to the 7th power) with zenith angles theta or = 45 deg and axes within the array are analyzed.

Atrashkevich, V. G.↗
NASA NTRS1984

Thematic Mapper simulator research for forest resource mapping in the Clearwater National Forest, Idaho

Per-pixel maximum likelihood digital classification and photo interpretation of Thematic Mapper Simulator (TMS) composited images for a managed conifer forest were used to evaluate both land cover and forest structure characteristics. TMS channels 4, 7, 5 and 3, which were found to be optimal for forest vegetation analysis, used the full range of the Thematic Mapper's spectral capability. Photo interpretation results indicate that a false color composite from TMS channels 4, 7, and 2 provided the highest accuracies; the combination of improved spatial, spectral and radiometric resolution of the Thematic Mapper yielded greater sensitivity to forest structural characteristics.

Brass, J. A.↗
NASA NTRS1983

The Einstein observatory medium sensitivity survey - The quasars sample

A complete sample of X-ray-selected quasars and Seyfert galaxies extracted from the Einstein Observatory Medium Sensitivity Survey is described, and their physical characteristics are discussed. A Hubble constant of 50 km/s per Mpc and a Friedmann universe with a deceleration parameter of q(0)=0 are assumed throughout the survey, and the sample of X-ray sources was selected according to the following criteria: the significance of the detection exceeds a confidence level of 5 beta; the source is physically unrelated to the target of the IPC observation; and that the source is at a galactic latitude higher than 20 deg. The redshift and optical luminosity distributions of 55 Active Galactic Nuclei (AGNs) detected in the survey are discussed. A number flux relation for the different classes of extragalactic objects are analyzed in detail, using a Maximum Likelihood method and the assumption that the relation can be represented as a power law.

Gioia, I. M.↗
NASA NTRS1983

Impact of thematic mapper sensor characteristics on classification accuracy

A three factor (spectral, spatial, and radiometric resolution), two level (TM and MSS) analysis of variance (ANOVA) approach allowed evaluation of the effects of each factor individually and in all possible combinations. Digital classification accuracy was used as the figure of merit. Nine study sites in Washington, DC, each of approximately 256 x 256 TM pixels, were randomly selected from the full scene for analysis. These results strongly suggest that the quantization level improvements and the addition of new spectral bands in the visible and middle IR regions (both afforded by the TM sensor design) can result in improved capabilities to accurately delineate land cover categories using a per point Gaussian maximum likelihood classifier. On the other hand, results indicate that the increase in spatial resolution to 30 m does not significantly enhance classification accuracy. The spatial result points to an inherent limitation of a per point classifier and to the need to improve data analysis techniques to handle high spatial resolution data.

Williams, D. L.↗
NASA NTRS1983

Spaceborne SAR data for land-cover classification and change detection

Supervised maximum-likelihood classifications of Seasat, SIR-A, and Landsat pixel data demonstrated that SIR-A data provided the most accurate discrimination (72 percent) between five land-cover categories. Spatial averaging of the SAR data improved classification accuracy significantly due to a reduction in both fading and within-field variability. The best multichannel classification accuracy (97.5 percent) was achieved by combining the SIR-A data with two Seasat images (ascending and descending orbits). In addition, semiquantitative analysis of Seasat-A digital data shows that orbital SAR imagery can be successfully used for multitemporal detection of change related to hydrologic and agronomic conditions by using simple machine processing techniques.

Brisco, B.↗
NASA NTRS1983

Feature selection and information content of thematic mapper simulator data for a forested environment

Feature selection and the information content of Thematic Mapper Simulator (TMS) data are investigated for a forested region in northern Idaho. The optimal TMS channels for forest structural characteristics are determined, and the capability of TMS data to describe the structural variability within a forest stand is evaluated. The comparative performance of TMS and MSS data to discriminate forest structural factors using per-pixel maximum likelihood classification is examined, and four optimal TMS channels are classified in order to ascertain if the full complement of TM channels provide higher accuracies than the four optimal ones.

Spanner, M. A.↗
NASA NTRS1984

Estimation of parameters in linear structural relationships Sensitivity to the choice of the ratio of error variances

Maximum likelihood estimation of parameters in linear structural relationships under normality assumptions requires knowledge of one or more of the model parameters if no replication is available. The most common assumption added to the model definition is that the ratio of the error variances of the response and predictor variates is known. This paper investigates the use of asymptotic formulae for variances and mean squared errors as a function of sample size and the assumed value for the error variance ratio.

Lakshminarayanan, M. Y.↗
NASA NTRS1983

High dynamic, low volume GPS receiver

A new GPS receiver concept and design are presented to meet the high dynamic and low volume requirements for range applications in missiles and drones. The receiver has the potential to satisfy all range requirements with one basic receiver, which has significant potential economic benefit over the alternate approach of using a family of receivers, each tailored for specific applications. The main new concept is to use approximate maximum likelihood estimates of pseudo range and range-rate, rather than tracking with carrier phase locked loops and code delay locked loops. Preliminary analysis indicates that receivers accelerating at 50 g or more can track with position errors due to acceleration of approximately 0.2 m/g, or 10 m at 50 g. Implementation is almost entirely digital to meet the low volume requirements.

Hurd, W. J.↗
NASA NTRS1985

Time-resolved speckle effects on the estimation of laser-pulse arrival times

A maximum-likelihood (ML) estimator of the pulse arrival in laser ranging and altimetry is derived for the case of a pulse distorted by shot noise and time-resolved speckle. The performance of the estimator is evaluated for pulse reflections from flat diffuse targets and compared with the performance of a suboptimal centroid estimator and a suboptimal Bar-David ML estimator derived under the assumption of no speckle. In the large-signal limit the accuracy of the estimator was found to improve as the width of the receiver observational interval increases. The timing performance of the estimator is expected to be highly sensitive to background noise when the received pulse energy is high and the receiver observational interval is large. Finally, in the speckle-limited regime the ML estimator performs considerably better than the suboptimal estimators.

Tsai, B.-M.↗
NASA NTRS1985

Einstein X-ray survey of the Pleiades - The dependence of X-ray emission on stellar age

The data obtained with two pointed observations of 1 deg by 1 deg fields of the Pleiades region have been analyzed, and the results are presented. The maximum-likelihood X-ray luminosity functions for the Pleiades G and K stars in the cluster are derived, and it is shown that, for the G stars, the Pleiades X-ray luminosity function is significantly brighter than the corresponding function for Hyades G dwarf stars. This finding indicates a dependence of X-ray luminosity on stellar age, which is confirmed by comparison of the same data with median X-ray luminosities of pre-main sequence and local disk population dwarf G stars. It is suggested that the significantly larger number of bright X-ray sources associated with G stars than with K stars, the lack of detection of M stars, and the relatively rapid rotation of the Pleiades K stars can be explained in terms of the onset of internal differential rotation near the convective envelope-radidative core interface after the spin-up phase during evolution to the main sequence.

Micela, G.↗
NASA NTRS1985

On the identification of a highly augmented airplane

The results of applying linear least squares and maximum likelihood estimation procedures to flight data from the AFTI/F-16 airplane are presented. Data from two flight control system modes are analyzed. It is shown that though a simple aerodynamic model structure is adequate for the simple mode, a more complicated model is necessary to adequately describe the highly augmented mode. The effect of augmentation of roll control is shown to be visible in the control parameters.

Batterson, J. G.↗
NASA NTRS1985

Statistical methods for astronomical data with upper limits. I - Univariate distributions

The statistical treatment of univariate censored data is discussed. A heuristic derivation of the Kaplan-Meier maximum-likelihood estimator from first principles is presented which results in an expression amenable to analytic error analysis. Methods for comparing two or more censored samples are given along with simple computational examples, stressing the fact that most astronomical problems involve upper limits while the standard mathematical methods require lower limits. The application of univariate survival analysis to six data sets in the recent astrophysical literature is described, and various aspects of the use of survival analysis in astronomy, such as the limitations of various two-sample tests and the role of parametric modelling, are discussed.

Feigelson, E. D.↗
NASA NTRS1985

Identification of integro-differential systems for application to unsteady aerodynamics and aeroelasticity

Integrodifferential equations for unsteady aerodynamic and aeroelastic phenomena are identified by means of several approaches. When the product of the frequency of motion and maximum time delay is much smaller than unity, the integral term can be approximated by a constant; when greater than unity, however, approximation of the integral is not possible. Approximations of integrodifferential models are needed to obtain identifiability. While the least-squares method may be used for model determination, the maximum likelihood technique is needed for accurate parameter estimation. High angle of attack and post stall/spin regions appear to have characteristics that can be satisfied by indicial models.

Gupta, N. K.↗
NASA NTRS1985

Performance comparisons between information extraction techniques using variable spatial resolution data

The decreased instantaneous field of view (IFOV) is one of the principal advances noted for the Thematic Mapper (TM) sensor. The 42.5 microradian IFOV of TM and the 710 km nominal orbit altitude result in a 30 m nominal spatial resolution at the earth surface. This is a considerable decrease in the projected pixel area when compared to the 79 m nominal spatial resolution of the Landsat Multispectral Scanner (MSS). An experiment was conducted which allowed a rigorous test of the influence of classifier design, with data spatial resolution of TM (30 m) and approximately that of the Landsat MSS (90 m), on classification performance for a particular TM scene. The experiment involved evaluation of the results for the per-point Gaussian maximum likelihood (GML) classifier and the supervised ECHO (Extraction and Classification of Homogeneous Objects) classifier.

Latty, R. S.↗
NASA NTRS1985

Decoding convolutionally encoded images

Maximum Likelihood Convolutional Decoding, which is used by the Deep Space Network for short constraint-length convolutional codes, assumes that all strings of information bits are equally likely. In some cases, like image data, this is not the case. The use of information about an adjacent pixel in decoding convolutionally encoded Voyager images is examined. It is discovered that, in a region of interest, as much as 2 dB may be gained.

Pitt, G. H., III↗