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NASA NTRS2008

Potential Use of a Bayesian Network for Discriminating Flash Type from Future GOES-R Geostationary Lightning Mapper (GLM) data

Continuous monitoring of the ratio of cloud flashes to ground flashes may provide a better understanding of thunderstorm dynamics, intensification, and evolution, and it may be useful in severe weather warning. The National Lighting Detection Network TM (NLDN) senses ground flashes with exceptional detection efficiency and accuracy over most of the continental United States. A proposed Geostationary Lightning Mapper (GLM) aboard the Geostationary Operational Environmental Satellite (GOES-R) will look at the western hemisphere, and among the lightning data products to be made available will be the fundamental optical flash parameters for both cloud and ground flashes: radiance, area, duration, number of optical groups, and number of optical events. Previous studies have demonstrated that the optical flash parameter statistics of ground and cloud lightning, which are observable from space, are significantly different. This study investigates a Bayesian network methodology for discriminating lightning flash type (ground or cloud) using the lightning optical data and ancillary GOES-R data. A Directed Acyclic Graph (DAG) is set up with lightning as a "root" and data observed by GLM as the "leaves." This allows for a direct calculation of the joint probability distribution function for the lighting type and radiance, area, etc. Initially, the conditional probabilities that will be required can be estimated from the Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) together with NLDN data. Directly manipulating the joint distribution will yield the conditional probability that a lightning flash is a ground flash given the evidence, which consists of the observed lightning optical data [and possibly cloud data retrieved from the GOES-R Advanced Baseline Imager (ABI) in a more mature Bayesian network configuration]. Later, actual GLM and NLDN data can be used to refine the estimates of the conditional probabilities used in the model; i.e., the Bayesian network is a learning network. Methods for efficient calculation of the conditional probabilities (e.g., an algorithm using junction trees), finding data conflicts, goodness of fit, and dealing with missing data will also be addressed.

Solakiewiz, Richard↗

NASA NTRS1995

The X-ray properties of the young open cluster around alpha Persei

The observations of the 50 Myr old alpha Persei open cluster, performed by the Rosat's position sensitive proportional counter (PSPC), are discussed. The X-ray observations cover an area of about 10 sq deg. A total of 160 X-ray sources were detected. The comparison between the X-ray luminosity distribution functions of the alpha Persei sample and the Pleiades indicated that F and G-type stars in the alpha Persei are more X-ray luminous than their older counterparts in the Pleiades. No significant difference was found between the distributions of the K and M-type dwarfs in the two clusters.

Randich, S.↗

NASA NTRS1995

Non-gyrotropic proton and alpha-particle velocity distributions in the solar wind: TAUS observations and stability analysis

Ion velocity distribution functions have been measured with high time resolution by the TAUS plasma instrument on the PHOBOS mission to Mars in 1989. The unambiguous separation of protons and alpha-particles by TAUS enabled us to study the nonthermal features of their distributions separately and to analyze the stability of the distributions against excitation of waves in the cyclotron-frequency domain. Typical nonthermal features include temperature anisotropies, with T(sub perpendicular) larger than T(sub parallel), and ion beam populations drifting along the local magnetic field direction. Also, distinctly non-gyrotropic alpha-particle velocity distributions were sometimes found. Non-gyrotropy strongly changes the wave dispersion and gives rise to new growing modes, related to the coupling of the standard wave modes existing in gyrotropic plasma. It is found that for the measured non-gyrotropic ion distributions the right-hand polarized wave can also be excited by a temperature anistropy instead of the usual beam drift.

Astudillo, H. F.↗

NASA NTRS2007

Analytic Guidance for the First Entry in a Skip Atmospheric Entry

This paper presents an analytic method to generate a reference drag trajectory for the first entry portion of a skip atmospheric entry. The drag reference, expressed as a polynomial function of the velocity, will meet the conditions necessary to fit the requirements of the complete entry phase. The generic method proposed to generate the drag reference profile is further simplified by thinking of the drag and the velocity as density and cumulative distribution functions respectively. With this notion it will be shown that the reference drag profile can be obtained by solving a linear algebraic system of equations. The resulting drag profile is flown using the feedback linearization method of differential geometric control as guidance law with the error dynamics of a second order homogeneous equation in the form of a damped oscillator. This approach was first proposed as a revisited version of the Space Shuttle Orbiter entry guidance. However, this paper will show that it can be used to fly the first entry in a skip entry trajectory. In doing so, the gains in the error dynamics will be changed at a certain point along the trajectory to improve the tracking performance.

Garcia-Llama, Eduardo↗

NASA NTRS2016

Polarbrdf: A General Purpose Python Package for Visualization Quantitative Analysis of Multi-Angular Remote Sensing Measurements

The Bidirectional Reflectance Distribution Function (BRDF) is a fundamental concept for characterizing the reflectance property of a surface, and helps in the analysis of remote sensing data from satellite, airborne and surface platforms. Multi-angular remote sensing measurements are required for the development and evaluation of BRDF models for improved characterization of surface properties. However, multi-angular data and the associated BRDF models are typically multidimensional involving multi-angular and multi-wavelength information. Effective visualization of such complex multidimensional measurements for different wavelength combinations is presently somewhat lacking in the literature, and could serve as a potentially useful research and teaching tool in aiding both interpretation and analysis of BRDF measurements. This article describes a newly developed software package in Python (PolarBRDF) to help visualize and analyze multi-angular data in polar and False Color Composite (FCC) forms. PolarBRDF also includes functionalities for computing important multi-angular reflectance/albedo parameters including spectral albedo, principal plane reflectance and spectral reflectance slope. Application of PolarBRDF is demonstrated using various case studies obtained from airborne multi-angular remote sensing measurements using NASA's Cloud Absorption Radiometer (CAR). Our visualization program also provides functionalities for untangling complex surface/atmosphere features embedded in pixel-based remote sensing measurements, such as the FCC imagery generation of BRDF measurements of grasslands in the presence of wild fire smoke and clouds. Furthermore, PolarBRDF also provides quantitative information of the angular distribution of scattered surface/atmosphere radiation, in the form of relevant BRDF variables such as sunglint, hotspot and scattering statistics.

CAR↗

NASA NTRS1975

Theory of fluctuations of extended air showers

The Monte Carlo method was used to calculate the probability distribution functions of shower characteristics for primary protons at sea level. The calculation was based on the following model of the elementary event: the interaction paths are 90 g/sq cm for nucleons and 120 g/sq cm for pions. The nonelasticity coefficient for nucleons is uniformly distributed between 0.1 and 0.9, and for pions it is equal to 1. Isobaric pions are taken into account. The spectra of secondary particles were determined using Cocconi's approximation formula. The calculation for the nuclei was carried out on the assumption of a breakup of the nucleus into component nucleons. The mean number of particles and the variances of the distributions for electrons when the number of muons was fixed, and for muons when the number of electrons was fixed, were calculated.

Dedenko, L. G.↗

NASA NTRS1974

Acoustical theory of turbulence

Fluid functions are expanded in a series of functions constituting a complete and orthogonal system of wave solutions of the linearized Navier-Stokes system. The motion of characteristic waves is described by Hamiltonian equations of ray acoustics. Amplitude of the waves is described with the aid of nonlinear interaction terms. The distribution functions (squares of amplitudes) satisfy Boltzmann-type equations and completely describe the mean turbulence properties.

Kentzer, C. P.↗

NASA NTRS1995

Theoretical study of hole initiated impact ionization in bulk silicon and GaAs using a wave-vector-dependent numerical transition rate formulation within an ensemble Monte Carlo calculation

In this paper, calculations of the hole initiated interband impact ionization rate in bulk silicon and GaAs are presented based on an ensemble Monte Carlo simulation with the inclusion of a wave-vector-dependent numerical transition rate formulation. The ionization transition rate is determined for each of the three valence bands, heavy, light, and split-off, using Fermi's golden rule with a two-body, screened Coulomb interaction. The dielectric function used within the calculation is assumed to be wave-vector-dependent. Calculations of the field-dependent impact ionization rate as well as the quantum yield are presented. It is found from both the quantum yield results and examination of the hole distribution function that the effective threshold energy for hole initiated impact ionization is relatively soft, similar to that predicted for the corresponding electron initiated ionization events occur more frequently than either heavy or split-offf initiated ionization events in bulk silicon over the applied electric field strengths examined here, 250-500 kV/cm. Conversely,in GaAs, the vast majority of hole initated ionization events originate from holes within the split-off band.

Oguzman, Ismail H.↗

NASA NTRS2004

Plasma Dispersion Function for the Kappa Distribution

The plasma dispersion function is computed for a homogeneous isotropic plasma in which the particle velocities are distributed according to a Kappa distribution. An ordinary differential equation is derived for the plasma dispersion function and it is shown that the solution can be written in terms of Gauss' hypergeometric function. Using the extensive theory of the hypergeometric function, various mathematical properties of the plasma dispersion function are derived including symmetry relations, series expansions, integral representations, and closed form expressions for integer and half-integer values of K.

Podesta, John J.↗

NASA NTRS1982

Continued development of a detailed model of arc discharge dynamics

Using a previously developed set of codes (SEMC, CASCAD, ACORN), a parametric study was performed to quantify the parameters which describe the development of a single electron indicated avalanche into a negative tip streamer. The electron distribution function in Teflon is presented for values of the electric field in the range of four-hundred million volts/meter to four billon volts/meter. A formulation of the scattering parameters is developed which shows that the transport can be represented by three independent variables. The distribution of ionization sites is used to indicate an avalanche. The self consistent evolution of the avalanche is computed over the parameter range of scattering set.

Beers, B. L.↗

NASA NTRS1984

Characteristics of suprathermal H(+) and He(++) in plasmoids in the distant magnetotail

Rest frame distribution functions were obtained for suprathermal H(+) and He(2+) ions during 20 particle intensity increases that were observed in the distant magnetotail by ISEE-3. All of these increases were characterized by isotropic, approximately 100-keV electrons, preceded by beaming electrons and velocity-dispersed protons distributions whose signatures are typically associated with plasmoids. In each of the plasmoids, both H(+) and He(2+) are found to be convected tailward, with speeds that range from 200 to 1000 km/sec. The acceleration mechanism is found to depend on particle velocity, and it is established that the solar wind is a dominant plasma source. The plasmoids appear to be expanding at about 100 km/sec during their tailward propagation.

Gloeckler, G.↗

NASA NTRS1992

Experimenter's data package for the descending layers rocket

In response to a proposal from Science Applications International Corporation (SAIC), NASA Headquarters has approved a sounding rocket mission designed to study the physics of intermediate layers in the Earth's ionosphere at middle latitudes. The experiment will be carried out by a team of scientists and engineers from the NASA Wallops Flight Facility, SAIC, the NASA Goddard Space Flight Center, and the Millstone Hill radar observatory. The mission will involve the launch of an instrumented sounding rocket from the Wallops Island rocket range in the summer of 1994, with the objective of penetrating a descending ionized layer in the E-region between altitudes of 115 and 140 km. Instrumentation aboard the rocket will measure the ion and neutral composition of the layer, its plasma density, driving wind and electric field forces, the thermal ion distribution function, and electron temperature. Depending on payload weight constraints and subject to availability, a particle detector to measure energetic ion and/or electron fluxes near the layer may also be included. This document was prepared as a reference for the NASA payload development and experiment teams, for distribution at the Project Initiation Conference (PIC). The design specifications discussed herein are therefore of a preliminary nature; the intent is to promote open discussions between experimenters and NASA engineers that will lead to a final design capable of achieving the experiment objectives.

Earle, Greg↗

NASA NTRS1993

Structure of Soot-Containing Laminar Jet Diffusion Flames

The structure and soot properties of nonbuoyant and weakly-buoyant round jet diffusion flames were studied, considering ethylene, propane and acetylene burning in air at pressures of 0.125-2.0 atm. Measurements of flame structure included radiative heat loss fractions, flame shape and temperature distributions in the fuel-lean (overfire) region. These measurements were used to evaluate flame structure predictions based on the conserved-scalar formalism in conjunction with the laminar flamelet concept, finding good agreement betweem predictions and measurements. Soot property measurements included laminar smoke points, soot volume function distributions using laser extinction, and soot structure using thermophoretic sampling and analysis by transmission electron microscopy. Nonbuoyant flames were found to exhibit laminar smoke points like buoyant flames but their properties are very different; in particular, nonbuoyant flames have laminar smoke point flame lengths and residence times that are shorter and longer, respectively, than buoyant flames.

Mortazavi, S.↗

NASA NTRS1993

LRAT: Lightning Radiative Transfer

In this report, we extend to cloud physics the work done for single and multiple scattering of electromagnetic waves. We consider the scattering of light, visible or infrared, by a spherical cloud represented by a statistically homogeneous ensemble of configurations of N identical spherical water droplets whose centers are uniformly distributed in its volume V. The ensemble is specified by the average number rho of scatterers in unit volume and by rho f(R) with f(R) as the distribution function for separations R of pairs. The incident light, vector-phi(sub 0) a plane electromagnetic wave with harmonic time dependence, is from outside the cloud. The propagation parameter kappa(sub 0) and the index of refraction eta(sub 0) determine physically the medium outside the distribution of scatterers. We solve the interior problem separately to obtain the bulk parameters for the scatterer equivalent to the ensemble of spherical droplets. With the interior solution or the equivalent medium approach, the multiple scattering problem is reduced to that of an equivalent single scatterer excited from outside illumination. A dispersion relation which determines the bulk propagation parameter K and the bulk index of refraction eta of the cloud is given in terms of the vector equivalent scattering amplitude vector-G and the dyadic scattering amplitude tilde-g of the single object in isolation. Based on this transfer model we will have the ability to consider clouds composed of inhomogeneous distribution of water and/or ice particles and we will be able to take into account particle size distributions within the cloud. We will also be able to study the effects of cloud composition (i.e., particle shape, size, composition, orientation, location) on the polarization of the single or the multiple scattered waves. Finally, this study will provide a new starting point for studying the problem of lightning radiative transfer.

Phanord, Dieudonne D.↗

NASA NTRS1990

Kinetic hydromagnetic instabilities due to a spherical shell distribution of pickup ions

The stability of a spherical shell ion distribution function against low-frequency hydromagnetic waves is discussed by relaxing the assumption of parallel propagation which was imposed in the preceding discussions published in the literature. It is found that Alfven waves as well as magnetosonic waves with oblique angles of propagation can be excited by a shell distribution. In the present analysis, the emphasis is placed on the case in which the thickness of the spherical shell is small.

Wu, C. S.↗

NASA NTRS1971

Binder model system to be used for determination of prepolymer functionality

Development of a method for determining the functionality distribution of prepolymers used for rocket binders is discussed. Research has been concerned with accurately determining the gel point of a model polyester system containing a single trifunctional crosslinker, and the application of these methods to more complicated model systems containing a second trifunctional crosslinker, monofunctional ingredients, or a higher functionality crosslinker. Correlations of observed with theoretical gel points for these systems would allow the methods to be applied directly to prepolymers.

Martinelli, F. J.↗

NASA NTRS1975

Rough-to-smooth transition of an equilibrium neutral constant stress layer

Purpose of research on rough-to-smooth transition of an equilibrium neutral constant stress layer is to develop a model for low-level atmospheric flow over terrains of abruptly changing roughness, such as those occurring near the windward end of a landing strip, and to use the model to derive functions which define the extent of the region affected by the roughness change and allow adequate prediction of wind and shear stress profiles at all points within the region. A model consisting of two bounding logarithmic layers and an intermediate velocity defect layer is assumed, and dimensionless velocity and stress distribution functions which meet all boundary and matching conditions are hypothesized. The functions are used in an asymptotic form of the equation of motion to derive a relation which governs the growth of the internal boundary layer. The growth relation is used to predict variation of surface shear stress.

Logan, E., Jr.↗

NASA NTRS1984

A kinetic cyclotron maser instability associated with a hollow beam of electrons

A kinetic cyclotron maser instability associated with a hollow-beam distribution function is studied. The instability differs from that discussed for the gyrotron device in two respects: in the present case the momentum dispersion is substantial, and furthermore there exists a low-energy background plasma. On the basis of physical arguments it can be demonstrated that the hollow-beam distribution is far more unstable than the loss cone distribution which has been extensively investigated in recent years. A criterion for maximum growth rate is established on the basis of consideration of the resonance ellipse. The validity of this criterion is supported by the results of numerical calculation.

Wu, C. S.↗