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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Singular spectrum analysis in nonlinear dynamics, with applications to paleoclimatic time series

Two dimensions of a dynamical system given by experimental time series are distinguished. Statistical dimension gives a theoretical upper bound for the minimal number of degrees of freedom required to describe the attractor up to the accuracy of the data, taking into account sampling and noise problems. The dynamical dimension is the intrinsic dimension of the attractor and does not depend on the quality of the data. Singular Spectrum Analysis (SSA) provides estimates of the statistical dimension. SSA also describes the main physical phenomena reflected by the data. It gives adaptive spectral filters associated with the dominant oscillations of the system and clarifies the noise characteristics of the data. SSA is applied to four paleoclimatic records. The principal climatic oscillations and the regime changes in their amplitude are detected. About 10 degrees of freedom are statistically significant in the data. Large noise and insufficient sample length do not allow reliable estimates of the dynamical dimension.

Vautard, R.↗
NASA NTRS1979

The importance of surface recombination and energy-bandgap narrowing in p-n-junction silicon solar cells

Experimental data demonstrating the sensitivity of open-circuit voltage to front-surface conditions are presented for a variety of p-n-junction silicon solar cells. Analytical models accounting for the data are defined and supported by additional experiments. The models and the data imply that a) surface recombination significantly limits the open-circuit voltage (and the short-circuit current) of typical silicon cells, and b) energy-bandgap narrowing is important in the manifestation of these limitations. The models suggest modifications in both the structural design and the fabrication processing of the cells that would result in substantial improvements in cell performance. The benefits of one such modification - the addition of a thin thermal silicon-dioxide layer on the front surface - are indicated experimentally.

Fossum, J. G.↗
NASA NTRS1996

Combined Industry, Space and Earth Science Data Compression Workshop

The sixth annual Space and Earth Science Data Compression Workshop and the third annual Data Compression Industry Workshop were held as a single combined workshop. The workshop was held April 4, 1996 in Snowbird, Utah in conjunction with the 1996 IEEE Data Compression Conference, which was held at the same location March 31 - April 3, 1996. The Space and Earth Science Data Compression sessions seek to explore opportunities for data compression to enhance the collection, analysis, and retrieval of space and earth science data. Of particular interest is data compression research that is integrated into, or has the potential to be integrated into, a particular space or earth science data information system. Preference is given to data compression research that takes into account the scien- tist's data requirements, and the constraints imposed by the data collection, transmission, distribution and archival systems.

Kiely, Aaron B.↗
NASA NTRS2013

Coarse-Grain Bandwidth Estimation Scheme for Large-Scale Network

A large-scale network that supports a large number of users can have an aggregate data rate of hundreds of Mbps at any time. High-fidelity simulation of a large-scale network might be too complicated and memory-intensive for typical commercial-off-the-shelf (COTS) tools. Unlike a large commercial wide-area-network (WAN) that shares diverse network resources among diverse users and has a complex topology that requires routing mechanism and flow control, the ground communication links of a space network operate under the assumption of a guaranteed dedicated bandwidth allocation between specific sparse endpoints in a star-like topology. This work solved the network design problem of estimating the bandwidths of a ground network architecture option that offer different service classes to meet the latency requirements of different user data types. In this work, a top-down analysis and simulation approach was created to size the bandwidths of a store-and-forward network for a given network topology, a mission traffic scenario, and a set of data types with different latency requirements. These techniques were used to estimate the WAN bandwidths of the ground links for different architecture options of the proposed Integrated Space Communication and Navigation (SCaN) Network. A new analytical approach, called the "leveling scheme," was developed to model the store-and-forward mechanism of the network data flow. The term "leveling" refers to the spreading of data across a longer time horizon without violating the corresponding latency requirement of the data type. Two versions of the leveling scheme were developed: 1. A straightforward version that simply spreads the data of each data type across the time horizon and doesn't take into account the interactions among data types within a pass, or between data types across overlapping passes at a network node, and is inherently sub-optimal. 2. Two-state Markov leveling scheme that takes into account the second order behavior of the store-and-forward mechanism, and the interactions among data types within a pass. The novelty of this approach lies in the modeling of the store-and-forward mechanism of each network node. The term store-and-forward refers to the data traffic regulation technique in which data is sent to an intermediate network node where they are temporarily stored and sent at a later time to the destination node or to another intermediate node. Store-and-forward can be applied to both space-based networks that have intermittent connectivity, and ground-based networks with deterministic connectivity. For groundbased networks, the store-and-forward mechanism is used to regulate the network data flow and link resource utilization such that the user data types can be delivered to their destination nodes without violating their respective latency requirements.

Cheung, Kar-Ming↗
NASA NTRS1981

A comparison of the thermal and radar characteristics of Mars

Results of thermal infrared sensing and radar observations of the Martian surface are compared for the region centered on +22 deg latitude. Values of the apparent thermal inertia of the surface were derived from surface brightnesses observed by the Viking Orbiter Infrared Thermal Mapper, while radar cross sections were obtained in earth-based experiments at wavelengths of 3.8, 12.5 and 70 cm. A correlation between the thermal inertia and radar cross section values is observed which is strongest with the 70-cm radar data except between longitudes of 10 and 90 deg, where a slight anticorrelation is found. The mixing of small (much less than 70 cm) rocks into a surface of fine material can account for the data between 90 and 370 deg longitude, with as much as 50% of the surface covered by rock in Syrtis Major, Isidis Planitia and parts of Elysium Planitia, and little or no rock cover near Olympus Mons, Elysium Mons, and Amazonis Planitia. The remaining longitudes may be explained in terms of the effects of atmospheric dust on the surface temperature or the effects of local variations in large-scale roughness or scattering from rocks. Data from the 90 to 370 deg longitude region are consistent with the division of the Martian surface into two types of terrain, possibly related to the erosional or depositional nature of the regions.

Jakosky, B. M.↗
DOE OSTI2025

H420 Imager Calibration Procedure: Field of View Scan

Gamma-ray imagers with coded apertures have a finite field of view (FOV) within which an image of a source can be generated. A “FOV scan” is a facet of imager calibration procedure that involves collecting specialized data for a range of source locations filling the FOV in order to understand and correct for differences in imager performance. Systematic distortions reveal relative displacements between internal imager components, which can be accounted for in data analysis. The success of this scan requires a stable imager position during the full measurement duration (~hours). This document summarizes the hardware and software tools required to conduct a FOV calibration scan of an H3D H420 Coded Aperture Gamma-Ray Imager.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1989

Seasonal variation of the 11 year solar cycle effect on the middle atmosphere: Role of the quasi biennial oscillation

Before the introduction of the Quasi Biennial Oscillation (Q.B.O.) in the study of the solar atmosphere relationship by Labitzke (1987) and Labitzke and Van Loon (1988), the only region of the atmosphere where an effect of a change in solar activity was generally admitted was the mesosphere. The response of the mesosphere, in phase with the solar activity, was found to be about one order of magnitude above model expectancy (around 10 to 20 Kelvin). It was observed independently of the season and maximized around 70 km (Chanin et al. 1987). However, from the same study, it was shown that the response of the stratosphere of opposite sign, clearly seen during winter and autumn, was at the threshold of detection in spring and summer. In the stratosphere, it was shown later that the separation of the data taking into account the sign of the Q.B.O. amplifies the negative correlation of the stratospheric temperature with solar activity in winter; it then becomes more significantly negative for the East phase of the Q.B.O. than when the data are all mixed (Labitzke and Chanin 1988). The studies of the seasonal response of the atmosphere to solar effect is crucial to understand the possible mechanism responsible of such a solar activity Q.B.O. relationship, knowing that the global dynamic circulation is quite different according to the seasons. The question is examined as to whether such separation of the data according to the phase of the Q.B.O. has any impact on the solar response of the middle atmosphere for seasons other than winter.

Keckhut, P.↗
NASA NTRS1993

Validation of multi-temperature nozzle flow code NOZNT

A computer code NOZNT (Nozzle in n-Temperatures), which calculates one-dimensional flows of partially dissociated and ionized air in an expanding nozzle, is tested against five existing sets of experimental data. The code accounts for: a) the differences among various temperatures, i.e., translational-rotational temperature, vibrational temperatures of individual molecular species, and electron-electronic temperature, b) radiative cooling, and c) the effects of impurities. The experimental data considered are: 1) the sodium line reversal and 2) the electron temperature and density data, both obtained in a shock tunnel, and 3) the spectroscopic emission data, 4) electron beam data on vibrational temperature, and 5) mass-spectrometric species concentration data, all obtained in arc-jet wind tunnels. It is shown that the impurities are most likely responsible for the observed phenomena in shock tunnels. For the arc-jet flows, impurities are inconsequential and the NOZNT code is validated by numerically reproducing the experimental data.

Park, Chul↗
NASA NTRS1993

The Space and Earth Science Data Compression Workshop

This document is the proceedings from a Space and Earth Science Data Compression Workshop, which was held on March 27, 1992, at the Snowbird Conference Center in Snowbird, Utah. This workshop was held in conjunction with the 1992 Data Compression Conference (DCC '92), which was held at the same location, March 24-26, 1992. The workshop explored opportunities for data compression to enhance the collection and analysis of space and Earth science data. The workshop consisted of eleven papers presented in four sessions. These papers describe research that is integrated into, or has the potential of being integrated into, a particular space and/or Earth science data information system. Presenters were encouraged to take into account the scientists's data requirements, and the constraints imposed by the data collection, transmission, distribution, and archival system.

Tilton, James C.↗
NASA NTRS1994

The 1994 Space and Earth Science Data Compression Workshop

This document is the proceedings from the fourth annual 'Space and Earth Science Data Compression Workshop,' which was held on April 2, 1994, at the University of Utah in Salt Lake City, Utah. This workshop was held in cooperation with the 1994 Data Compression Conference, which was held at Snowbird, Utah, March 29-31 1994. The Workshop explored opportunities for data compression to enhance the collection and analysis of space and Earth science data. It consisted of 13 papers presented in 4 sessions. The papers focus on data compression research that is integrated into, or has the potential to be integrated into, a particular space and/or Earth science data information system. Presenters were encouraged to take into account the scientist's data requirements, and the constraints imposed by the data collection, transmission, distribution, and archival system.

Tilton, James C.↗
NASA NTRS1977

SAMICS support study. Volume 1: Cost account catalog

The Jet Propulsion Laboratory (JPL) is examining the feasibility of a new industry to produce photovoltaic solar energy collectors similar to those used on spacecraft. To do this, a standardized costing procedure was developed. The Solar Array Manufacturing Industry Costing Standards (SAMICS) support study supplies the following information: (1) SAMICS critique; (2) Standard data base--cost account structure, expense item costs, inflation rates, indirect requirements relationships, and standard financial parameter values; (3) Facilities capital cost estimating relationships; (4) Conceptual plant designs; (5) Construction lead times; (6) Production start-up times; (7) Manufacturing price estimates.

Source record↗
NASA NTRS1979

Machine processing of remotely sensed data; Proceedings of the Fifth Annual Symposium, Purdue University, West Lafayette, Ind., June 27-29, 1979

Papers are presented on techniques and applications for the machine processing of remotely sensed data. Specific topics include the Landsat-D mission and thematic mapper, data preprocessing to account for atmospheric and solar illumination effects, sampling in crop area estimation, the LACIE program, the assessment of revegetation on surface mine land using color infrared aerial photography, the identification of surface-disturbed features through a nonparametric analysis of Landsat MSS data, the extraction of soil data in vegetated areas, and the transfer of remote sensing computer technology to developing nations. Attention is also given to the classification of multispectral remote sensing data using context, the use of guided clustering techniques for Landsat data analysis in forest land cover mapping, crop classification using an interactive color display, and future trends in image processing software and hardware.

Tendam, I. M.↗
NASA NTRS1985

On the geodetic applications of simultaneous range differences to Lageos

While the majority of the currently deployed satellite laser systems are of centimeter level precision, the accuracy of the geodetic products corresponds to the accuracy in which geodesists are interested. On several occasions, the best models are either not good enough or result in tedious computations which are required to achieve accuracies comparable to those of the observations. A possible alternative is related to the development of a new method of data analysis. This method involves the minimization of the effect of the systematic errors and, in particular, the minimization of errors arising from an incorrectly modeled orbit. The present paper provides a summary of the results of a study of this option, taking into account laser ranging data from Lageos.

Pavlis, E. C.↗
NASA NTRS2018

Modeling the Proton Radiation Belt With Van Allen Probes Relativistic Electron-Proton Telescope Data

An empirical model of the proton radiation belt is constructed from data taken during 2013-2017 by the Relativistic Electron-Proton Telescopes on the Van Allen Probes satellites. The model intensity is a function of time, kinetic energy in the range 18-600 megaelectronvolts, equatorial pitch angle, and L shell of proton guiding centers. Data are selected, on the basis of energy deposits in each of the nine silicon detectors, to reduce background caused by hard proton energy spectra at low L. Instrument response functions are computed by Monte Carlo integration, using simulated proton paths through a simplified structural model, to account for energy loss in shielding material for protons outside the nominal field of view. Overlap of energy channels, their wide angular response, and changing satellite orientation require the model dependencies on all three independent variables be determined simultaneously. This is done by least squares minimization with a customized steepest descent algorithm. Model uncertainty accounts for statistical data error and systematic error in the simulated instrument response. A proton energy spectrum is also computed from data taken during the 8 January 2014 solar event, to illustrate methods for the simpler case of an isotropic and homogeneous model distribution. Radiation belt and solar proton results are compared to intensities computed with a simplified, on-axis response that can provide a good approximation under limited circumstances.

Selesnick, R. S.↗
NASA NTRS1996

Closed-Loop System Identification Experience for Flight Control Law and Flying Qualities Evaluation of a High Performance Fighter Aircraft

This paper highlights some of the results and issues associated with estimating models to evaluate control law design methods and design criteria for advanced high performance aircraft. Experimental fighter aircraft such as the NASA-High Alpha Research Vehicle (HARV) have the capability to maneuver at very high angles of attack where nonlinear aerodynamics often predominate. HARV is an experimental F/A-18, configured with thrust vectoring and conformal actuated nose strakes. Identifying closed-loop models for this type of aircraft can be made difficult by nonlinearities and high order characteristics of the system. In this paper, only lateral-directional axes are considered since the lateral-directional control law was specifically designed to produce classical airplane responses normally expected with low-order, rigid-body systems. Evaluation of the control design methodology was made using low-order equivalent systems determined from flight and simulation. This allowed comparison of the closed-loop rigid-body dynamics achieved in flight with that designed in simulation. In flight, the On Board Excitation System was used to apply optimal inputs to lateral stick and pedals at five angles at attack : 5, 20, 30, 45, and 60 degrees. Data analysis and closed-loop model identification were done using frequency domain maximum likelihood. The structure of identified models was a linear state-space model reflecting classical 4th-order airplane dynamics. Input time delays associated with the high-order controller and aircraft system were accounted for in data preprocessing. A comparison of flight estimated models with small perturbation linear design models highlighted nonlinearities in the system and indicated that the closed-loop rigid-body dynamics were sensitive to input amplitudes at 20 and 30 degrees angle of attack.

Murphy, Patrick C.↗
NASA NTRS1999

Closed-Loop System Identification Experience for Flight Control Law and Flying Qualities Evaluation of a High Performance Fighter Aircraft

This paper highlights some of the results and issues associated with estimating models to evaluate control law design methods and design criteria for advanced high performance aircraft. Experimental fighter aircraft such as the NASA High Alpha Research Vehicle (HARV) have the capability to maneuver at very high angles of attack where nonlinear aerodynamics often predominate. HARV is an experimental F/A-18, configured with thrust vectoring and conformal actuated nose strakes. Identifying closed-loop models for this type of aircraft can be made difficult by nonlinearities and high-order characteristics of the system. In this paper only lateral-directional axes are considered since the lateral-directional control law was specifically designed to produce classical airplane responses normally expected with low-order, rigid-body systems. Evaluation of the control design methodology was made using low-order equivalent systems determined from flight and simulation. This allowed comparison of the closed-loop rigid-body dynamics achieved in flight with that designed in simulation. In flight, the On Board Excitation System was used to apply optimal inputs to lateral stick and pedals at five angles of attack: 5, 20, 30, 45, and 60 degrees. Data analysis and closed-loop model identification were done using frequency domain maximum likelihood. The structure of the identified models was a linear state-space model reflecting classical 4th-order airplane dynamics. Input time delays associated with the high-order controller and aircraft system were accounted for in data preprocessing. A comparison of flight estimated models with small perturbation linear design models highlighted nonlinearities in the system and indicated that the estimated closed-loop rigid-body dynamics were sensitive to input amplitudes at 20 and 30 degrees angle of attack.

Murphy, Patrick C.↗
NASA NTRS1977

Estimating costs and performance of systems for machine processing of remotely sensed data

This paper outlines a method for estimating computer processing times and costs incurred in producing information products from digital remotely sensed data. The method accounts for both computation and overhead, and may be applied to any serial computer. The method is applied to estimate the cost and computer time involved in producing Level II Land Use and Vegetative Cover Maps for a five-state midwestern region. The results show that the amount of data to be processed overloads some example computer systems, but that the processing is feasible on others.

Ballard, R. J.↗
NASA NTRS1978

A general panel sizing computer code and its application to composite structural panels

A computer code for obtaining the dimensions of optimum (least mass) stiffened composite structural panels is described. The procedure, which is based on nonlinear mathematical programming and a rigorous buckling analysis, is applicable to general cross sections under general loading conditions causing buckling. A simplified method of accounting for bow-type imperfections is also included. Design studies in the form of structural efficiency charts for axial compression loading are made with the code for blade and hat stiffened panels. The effects on panel mass of imperfections, material strength limitations, and panel stiffness requirements are also examined. Comparisons with previously published experimental data show that accounting for imperfections improves correlation between theory and experiment.

Anderson, M. S.↗