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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Ozone vertical distribution retrieval from ground-based high resolution infrared solar spectra

A practical procedure for the retrieval of ozone vertical profiles from ground-based high resolution Fourier transform infrared solar spectra has been developed. The analysis is based on a multilayer line-by-line forward model and a semi-empirical version of the optimal estimation inversion method of Rodgers. The 1002.6-1003.2 cm(exp -1) spectral interval has been selected for the analysis on the basis of synthetic spectrum calculations. This interval contains numerous ozone lines covering a range of intensities and providing retrieval sensitivity from ground level to about 35 km. Characterization of the method and an error analysis have been performed. For a spectral resolution of 0.05-0.01 cm(exp -1) and a signal-to-noise ratio greater than or equal to 100 the retrieval is stable with a vertical resolution of approximately 5 km attainable near the surface degrading to approximately 10 km in the stratosphere. Synthetic spectra studies show that the a priori profile and weak constraints selected for the retrievals introduce no significant biases for a wide range of ozone profiles.

Pougatchev, N. S.↗
NASA NTRS2016

Study of the Effect of Temporal Sampling Frequency on DSCOVR Observations Using the GEOS-5 Nature Run Results: Cloud Coverage - Part II

This is the second part of a study on how temporal sampling frequency affects satellite retrievals in support of the Deep Space Climate Observatory (DSCOVR) mission. Continuing from Part 1, which looked at Earth's radiation budget, this paper presents the effect of sampling frequency on DSCOVR-derived cloud fraction. The output from NASA's Goddard Earth Observing System version 5 (GEOS-5) Nature Run is used as the "truth". The effect of temporal resolution on potential DSCOVR observations is assessed by subsampling the full Nature Run data. A set of metrics, including uncertainty and absolute error in the subsampled time series, correlation between the original and the subsamples, and Fourier analysis have been used for this study. Results show that, for a given sampling frequency, the uncertainties in the annual mean cloud fraction of the sunlit half of the Earth are larger over land than over ocean. Analysis of correlation coefficients between the subsamples and the original time series demonstrates that even though sampling at certain longer time intervals may not increase the uncertainty in the mean, the subsampled time series is further and further away from the "truth" as the sampling interval becomes larger and larger. Fourier analysis shows that the simulated DSCOVR cloud fraction has underlying periodical features at certain time intervals, such as 8, 12, and 24 h. If the data is subsampled at these frequencies, the uncertainties in the mean cloud fraction are higher. These results provide helpful insights for the DSCOVR temporal sampling strategy.

GEOS-5↗
NASA NTRS1972

Spectral and polarization analysis of micropulsations observed at ATS-1

Results are reported for an analysis of low frequency oscillations in the earth's magnetic field as observed at the synchronous orbit by the magnetometer experiment on board ATS 1. Oscillations in the range .002 f .02 H3 for the period Dec. 1966 through Dec. 1967 were studied. The analysis combines a detailed, computer-processed, spectral analysis of selected events with a less detailed manual analysis of all events in the two year time interval from Dec. 1966 to Dec. 1968. The computer analysis revealed that a given event is often characterized by a dominat, narrow, spectral peak whose associated oscillations are almost entirely limited to a plane, together with several minor peaks. Dynamic spectral analyses revealed that minor spectral peaks appear as short isolated bursts. The sense of rotation of the perturbation vector tends to change from right-handed elliptical at the beginning of a burst to left-handed elliptical at the end. The major axis of the polarization ellipse is inclined by typically 30 deg east of radial.

Morris, W.↗
NASA NTRS1992

Development of a residual acceleration data reduction and dissemination plan

A major obstacle in evaluating the residual acceleration environment in an orbiting space laboratory is the amount of data collected during a given mission: gigabytes of data will be available as SAMS units begin to fly regularly. Investigators taking advantage of the reduced gravity conditions of space should not be overwhelmed by the accelerometer data which describe these conditions. We are therefore developing a data reduction and analysis plan that will allow principal investigators of low-g experiments to create experiment-specific residual acceleration data bases for post-flight analysis. The basic aspects of the plan can also be used to characterize the acceleration environment of earth orbiting laboratories. Our development of the reduction plan is based on the following program of research: the identification of experiment sensitivities by order of magnitude estimates and numerical modelling; evaluation of various signal processing techniques appropriate for the reduction, supplementation, and dissemination of residual acceleration data; and testing and implementation of the plan on existing acceleration data bases. The orientation of the residual acceleration vector with respect to some set of coordinate axes is important for experiments with known directional sensitivity. Orientation information can be obtained from the evaluation of direction cosines. Fourier analysis is commonly used to transform time history data into the frequency domain. Common spectral representations are the amplitude spectrum which gives the average of the components of the time series at each frequency and the power spectral density which indicates the power or energy present in the series per unit frequency interval. The data reduction and analysis scheme developed involves a two tiered structure to: (1) identify experiment characteristics and mission events that can be used to limit the amount of accelerator data an investigator should be interested in; and (2) process the data in a way that will be meaningful to the experiment objectives. A general outline of the plan is given.

Rogers, Melissa J. B.↗
NASA NTRS1999

Hard X-Ray Lags in GRO J1719--24

We have used the Fourier cross spectra of GRO J1719-24, obtained with BATSE, to estimate the phase lags between the X-ray flux variations in the 20 50 and 50-100 keV energy bands as a function of Fourier frequency in the interval 0.002-0.488 Hz. Our analysis covers the entire about 80 day X-ray outburst of this black hole candidate, following the first X-ray detection on 1993 September 25. The X-ray variations in the 50-100 keV band lag those in the 20-50 keV energy band by an approximately constant phase difference of 0.072 + 0.010 rad in the frequency interval 0.02-0.20 Hz. The peak phase lags in the interval 0.02-0.20 Hz are about twice those of Cyg X-1 and GRO J0422+32. These results are consistent with models for Comptonization regions composed of extended nonuniform clouds around the central source.

VanDerHooft, F.↗
NASA NTRS1998

Hard X-Ray Lags in GRO J1719-24

We have used the Fourier cross spectra of GRO J1719-24. as obtained with BATSE, to estimate the phase lags between the X-ray flux variations in the 20-,50 and 50-100 keV energy bands as a function of Fourier frequency in the interval 0.002-0.488 Hz. Our analysis covers the entire approximately 80 day X-ray outburst of this black-hole candidate, following the first X-ray detection on 1993 September 25. The X-ray variations in the 50-100 keV band, lag those in the 20-50 keV energy band by an approximately constant phase difference of 0.072 +/- 0.010 rad in the frequency interval 0.02-0.20 Hz. The time lags of GRO J1719-24 decrease with frequency as a power law, with index 1.04 +/- 0.13 for frequencies >/= 0.01 Hz. These results are discussed together with those obtained in recent similar studies of the black-hole candidates Cyg X-1 and GRO J0422+32.

VanderHooft, Frank↗
NASA NTRS1983

Creep testing of foil-gage metals at elevated temperature using an automated data acquisition system

A method is being developed to obtain creep data on foil gage metals at elevated temperatures using an automated data acquisition system in conjunction with a mechanically counter balanced extensometer. The automated system components include the Hewlett-Packard (HP) 9845A desktop computer, the HP 3455A digital voltmeter and the HP 3495A scanner. Software for test monitoring and data collection was developed; data manipulation, including curve plotting was done with a HP regression analysis software package. Initial creep tests were conducted on .003 in. thick foil specimens of Ti-6A1-4V at temperatures of 800 F and 1000 F and at stress levels of 25 ksi and 45 ksi. For comparison, duplicate tests were run on .049 in. thick specimens sheet of the same alloy. During testing, the furnace and specimen temperature, bridge voltage, strain and load output were automatically monitored and recorded at predetermined intervals. Using the HP regression analysis program, recorded strain output was plotted as a function of time. These resultant creep curves indicate that, under similar conditions of temperature and stress, foil gage specimens exhibit a higher creep rate than sheet specimens.

Blackburn, L. B.↗
NASA NTRS1993

Time variations of solar UV irradiance as measured by the SOLSTICE (UARS) instrument

An analysis is presented of solar ultraviolet irradiance measurements made by the SOLSTICE spectrometers on the Upper Atmosphere Research Satellite (UARS). Reported observations cover the wavelength interval 119-420 nm, and the analysis discussed here is for the time period 26 Nov 1991 to 31 Dec 1992, during which time solar activity decreased in intensity. At the time of peak activity, the average 27-day variation had a relative amplitude of about 8 percent at Ly-alpha, tailing off to about 0.6 percent at 260 nm. It is shown that over the spectral interval 119-260 nm, the relative 27-day harmonic was about a factor of two larger during the strongly disturbed as compared with the moderately disturbed period.

London, Julius↗
NASA NTRS2025

Gaussian Process for Flight Delay Prediction: Learning a Stochastic Process

This paper presents a machine-learning approach to predict flight delays. Whereas neural networks are extensively studied for predictive capabilities, they involve non-intuitive design and extensive analysis, particularly in training and optimization processes. Instead, the proposed framework employs Gaussian Processes as a supervised learning technique for flight delay prediction. This data-driven approach trains the model using prior information, specifically the mean and covariance tied to existing data. The proposed Gaussian Process Regression (GPR) model employs the day of flight as a pivotal feature for delay forecasting. We analyze flights from various routes and gauge the accuracy of the presented learning technique by comparing the predicted delays with the actual ones. Given the inherent challenges in precisely forecasting delays, we predict the delays with a 95 % confidence interval. Also, an error propagation analysis in the prediction horizon is carried out to determine the optimal time frame for prediction. The proposed method for flight delay prediction is important as airlines can strategize flight operations and issue timely advisories.

stochastic↗
NASA NTRS1999

Uncertainty Analysis of Inertial Model Attitude Sensor Calibration and Application with a Recommended New Calibration Method

Statistical tools, previously developed for nonlinear least-squares estimation of multivariate sensor calibration parameters and the associated calibration uncertainty analysis, have been applied to single- and multiple-axis inertial model attitude sensors used in wind tunnel testing to measure angle of attack and roll angle. The analysis provides confidence and prediction intervals of calibrated sensor measurement uncertainty as functions of applied input pitch and roll angles. A comparative performance study of various experimental designs for inertial sensor calibration is presented along with corroborating experimental data. The importance of replicated calibrations over extended time periods has been emphasized; replication provides independent estimates of calibration precision and bias uncertainties, statistical tests for calibration or modeling bias uncertainty, and statistical tests for sensor parameter drift over time. A set of recommendations for a new standardized model attitude sensor calibration method and usage procedures is included. The statistical information provided by these procedures is necessary for the uncertainty analysis of aerospace test results now required by users of industrial wind tunnel test facilities.

Tripp, John S.↗
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 NTRS1996

Validation of Spectral Analysis as a Noninvasive Tool to Assess Autonomic Regulation of Cardiovascular Function

A major focus of our program has been to develop a sensitive noninvasive procedure to quantify early weightlessness-induced changes in cardiovascular function or potential dysfunction. Forty studies of healthy young volunteers (10 men and 10 women, each studied twice) were conducted to determine changes in the sympatho-vagal balance of autonomic control of cardiovascular regulation during graded headward and footward blood volume shifts. Changes in sympatho-vagal balance were classified by changes in the mean levels and spectral content of cardiovascular variables and verified by changes in circulating levels of catecholamines and pancreatic polypeptide. Possible shifts in intra/extravascular fluid were assessed from changes in hematocrit and plasma mass density while changes in the stimulus to regulate plasma volume were determined from Plasma Renin Activity (PRA). Autonomic blockade was used to unmask the relative contribution of sympathetic and parasympathetic efferent influences in response to 10 min each of 0, 20 and 40 mmHg Lower Body Negative Pressure (LBNP) and 15 and 30 mmHg Positive Pressure (LBPP). The combination of muscarinic blockade with graded LBNP and LBPP was used to evoke graded increases and decreases in sympathetic activity without parasympathetic contributions. The combination of beta blockade with graded LBNP and LBPP was used to produce graded increases and decreases in parasympathetic activity without beta sympathetic contributions. Finally, a combination of both beta and muscarinic blockades with LBNP and LBPP was used to determine the contribution from other, primarily alpha adrenergic, sources. Mean values, spectral analyses and time frequency analysis of R-R interval (HR), Arterial Pressure (AP), peripheral blood flow (RF), Stroke Volume (SV) and peripheral resistance (TPR) were performed for all phases of the study. Skin blood Flow (SF) was also measured in other studies and similarly analyzed. Spectra were examined for changes in three frequency regions (low 0.006 - 0.005 Hz (LF), mid 0.05 - 0.15 Hz (W), and high 0.15 - 0.45 Hz (EF)). The primary objective of the study was to indicate which changes in the mean values and/or spectra of cardiovascular variables consistently correlated with changes in sympatho-vagal balance in response to headward and footward fluid shifts. A secondaey objective was to quantify the vascular and extravascular fluid shifts evoked by LBNP and LBPP. The principal hypothesis being tested was that headward fluid shifts would evoke an increase in parasympathetic activity and footward fluid shifts would evoke an increase in sympathetic activity both of which would be detected by spectral analysis and verified by circulating hormones. Hematocrit (HCT), plasma mass density and plasma renin activity increased with muscarinic blockade and with LBNP, a response indicative of a plasma shift to extravascular spaces. Beta blockade alone or after muscarinic blockade had no effect on HCT or plasma mass density. With respect to intravascular fluid volume distribution, LBNP and LBPP produced sufficient upper body vascular fluid shifts to evoke appropriate autonomic regulatory responses.

Knapp, Charles F.↗
NASA NTRS1986

Study of Travelling Interplanetary Phenomena (STIP) workshop travel

Thirty six abstracts are provided from the SCOSTEP/STIP Symposium on Retrospective Analyses and Future Coordinated Intervals held in Switzerland on June 10 to 12, 1985. Six American scientists participated in the symposium and their abstracts are also included. The titles of their papers are: (1) An analysis of near surface and coronal activity during STIP interval 12, by T. E. Gergely; (2) Helios images of STIP intervals 6, B. V. Jackson; (3) Results from the analysis of solar and interplanetary observations during STIP interval 7, S. R. Kane; (4) STIP interval 19, E. Cliver; (5) Hydrodynamic buoyancy force in the solar atmosphere, T. Yeh; and (6) A combined MHD modes for the energy and momentum transport from solar surface to interplanetary space, S. T. Wu.

Wu, S. T.↗
NASA NTRS2004

A DMAP Program for the Selection of Accelerometer Locations in MSC/NASTRAN

A new program for selecting sensor locations has been written in the DMAP (Direct Matrix Abstraction Program) language of MSC/NASTRAN. The program implements the method of Effective Independence for selecting sensor locations, and is executed within a single NASTRAN analysis as a "rigid format alter" to the normal modes solution sequence (SOL 103). The user of the program is able to choose among various analysis options using Case Control and Bulk Data entries. Algorithms tailored for the placement of both uni-axial and tri- axial accelerometers are available, as well as several options for including the model s mass distribution into the calculations. Target modes for the Effective Independence analysis are selected from the MSC/NASTRAN ASET modes calculated by the "SOL 103" solution sequence. The initial candidate sensor set is also under user control, and is selected from the ASET degrees of freedom. Analysis results are printed to the MSCINASTRAN output file (*.f06), and may include the current candidate sensors set, and their associated Effective Independence distribution, at user specified iteration intervals. At the conclusion of the analysis, the model is reduced to the final sensor set, and frequencies and orthogonality checks are printed. Example results are given for a pre-test analysis of NASA s five-segment solid rocket booster modal test.

Peck, Jeff↗
NASA NTRS1988

High degree interpolation polynomial in Newton form

Polynomial interpolation is an essential subject in numerical analysis. Dealing with a real interval, it is well known that even if f(x) is an analytic function, interpolating at equally spaced points can diverge. On the other hand, interpolating at the zeroes of the corresponding Chebyshev polynomial will converge. Using the Newton formula, this result of convergence is true only on the theoretical level. It is shown that the algorithm which computes the divided differences is numerically stable only if: (1) the interpolating points are arranged in a different order, and (2) the size of the interval is 4.

Tal-Ezer, Hillel↗
NASA NTRS1987

Expert systems tools for Hubble Space Telescope observation scheduling

This paper discusses the utility of expert systems techniques for Hubble Space Telescope (HST) planning and scheduling and describes a plan for development of expert system tools which will augment the existing ground system. Additional capabilities provided by these tools will include graphics-oriented plan evaluation, long-range analysis of the observation pool, analysis of optimal scheduling time intervals, constructing sequences of spacecraft activities which minimize operational overhead, and optimization of linkages between observations. Initial prototyping of a scheduler used the Automated Reasoning Tool running on a LISP workstation.

Miller, Glenn↗
NASA NTRS1987

Expert systems tools for Hubble Space Telescope observation scheduling

The utility of expert systems techniques for the Hubble Space Telescope (HST) planning and scheduling is discussed and a plan for development of expert system tools which will augment the existing ground system is described. Additional capabilities provided by these tools will include graphics-oriented plan evaluation, long-range analysis of the observation pool, analysis of optimal scheduling time intervals, constructing sequences of spacecraft activities which minimize operational overhead, and optimization of linkages between observations. Initial prototyping of a scheduler used the Automated Reasoning Tool running on a LISP workstation.

Miller, Glenn↗
NASA NTRS1986

Laser wavemeter/spectrometer operating manual

The Laser Wavemeter/Spectrometer is a compact, rugged instrument using a unique combination of an uncoated (Snyder) wedge interferometer and a coated (Fizeau) wedge interferometer to simultaneously measure the wavelength centroid and spectral characteristics of pulsed or CW lasers. Wavelength centroid measurement accuracies are in the range of 1 part in 1,000,000 using the Snyder stage alone. The Fizeau wedge section is capable of resolving spectral details to 0.002/cm and of locating the position of a fringe to 0.0005/cm. Because the Snyder wedge is uncoated, wavelength centroid measurements are possible over the entire detector range of from about 300 nm to greater than 1.0 micron. The coatings of the Fizeau wedge limit spectral analysis to a 200 nm interval in that range. The instrument is currently configured to operate from 600 nm to 800 nm.

Cotnoir, Leo J.↗