SEARCH · Engineering Papers

Results for “likelihood”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45

All sources NASA NTRS DOE OSTI

NASA NTRS1982

The use of LANDSAT data to monitor the urban growth of Sao Paulo Metropolitan area

Urban growth from 1977 to 1979 of the region between Billings and the Guarapiranga reservoir was mapped and the problematic urban areas identified using several LANDSAT products. Visual and automatic interpretation techniques were applied to the data. Computer compatible tapes of LANDSAT multispectral scanner data were analyzed through the maximum likelihood Gaussian algorithm. The feasibility of monitoring fast urban growth by remote sensing techniques for efficient urban planning and control is demonstrated.

Dejesusparada, N.↗

NASA NTRS1982

Parametric identification of human operator models

The accurate and efficient identification of the human operator is still a need in human factors engineering especially concerning multivariable control. Control theoretic identification methods need to be tested with human operator models under realistic boundary conditons. The requirements and criteria for the use of parametric methods, selected models as well as the Maximum Likelihood Method and the Extended Kalman Filter are displayed. The experiments and results are comparatively discussed from the point of practical engineering.

Ninz, N. R.↗

NASA NTRS1981

VLA observations of solar active regions at 6 cm wavelength

Synthesized maps of two solar active regions obtained from observations with the Very Large Array (VLA) with 9-arcsec resolution are presented. The most intense sources in these regions are found to be associated with filamentary structures and magnetic neutral lines as shown in H-alpha and photospheric magnetograms. These sources are not located directly over sunspots in disagreement with earlier observations. EUV and X-ray observations have suggested that similar structures should be visible at cm wavelengths around but, outside of, sunspots if the magnetic field is sufficiently strong. These results are consistent with the locations of hot (greater than 1,000,000 K) plasmas in active regions expected from generalization based on optical photographs. Given the sizes of the radio sources, the volume emission measures of soft X-rays observed from OSO-8 rule out the possibility of thermal bremsstrahlung being of any significance, as far as the 6 cm emission is concerned. Therefore, gyroresonance absorption process is the most likely cause of 6 cm emission from these sources, and its likelihood is enhanced by the magnetic field geometry that is known to exist over filaments and neutral lines.

Kundu, M. R.↗

NASA NTRS1981

On matching the systems identification technique to the particular application

Several maximum likelihood and multiple regression parameter estimation programs are currently being used at the Langley Research Center of the NASA to analyze aircraft flight test data. Based on this wealth of experience, the pertinent features of these programs are investigated and some of the difficulties involved in their use are discussed. By comparing computational time, data requirements and accuracy needed, a strategy for determining which program can be used to the best advantage of the flight test engineer is discussed.

Suit, W. T.↗

NASA NTRS1981

Model degradation effects on sensor failure detection

This paper discusses the effects of imperfect modeling on the detection and isolation of sensor failures. For systems with non-zero set points, deterministic inputs or non-zero noise biases, the model mismatch appears as a bias on the stochastic innovation process. This bias, if left unaccounted for, would be sufficient to declare a false alarm failure in one or more sensors. A practical design procedure based upon the Generalized Likelihood Ratio (GLR) form uses a finite data window sequential t-test to detect and isolate model mismatch effects and soft sensor failures. Application to an eighth order model of the QCSEE turbofan engine is discussed.

Leininger, G. G.↗

NASA NTRS1981

Selected stability and control derivatives from the first Space Shuttle entry

Primary stability and control derivative estimates garnered from the first Shuttle entry are reported. The craft was the first vehicle to maneuver over a wide range of hypersonic velocities, yielding data on flight characteristics from previously unexplored regimes. The flight envelope was confined to entry and safe landing, with no additional maneuvers to gain control data. Data for a Mach number range of 25-1.5 and altitudes of 515,000-50,000 ft are provided, and functional ranges of the Shuttle control surfaces and attitude jets are outlined. On-board systems gathered data on aerodynamic coefficient identification, flight condition and Euler angles, and jet chamber pressures. A maximum likelihood estimation program, which contained unknown stability and control derivatives, was used for control; a control input determined the value of the unknown derivatives, and the input and spacecraft response were measured. Longitudinal and lateral directional maneuvers and their derivative estimates are described, noting wind contamination of the sideslip measurements below Mach 3. Further maneuvering and stability tests are projected for subsequent flights.

Iliff, K. W.↗

NASA NTRS1981

Stability of goethite /alpha-FeOOH/ and lepidocrocite /gamma-FeOOH/ to dehydration by UV radiation - Implications for their occurrence on the Martian surface

The geochemistry of the FeOOH polymorphs is an important consideration when evaluating the likelihood of an occurrence of detectable amounts of these minerals on Mars. An investigation is conducted regarding the stability of the FeOOH polymorphs geothite and lepidocrocite to dehydration in the presence of UV radiation. A thorough characterization of the FeOOH powders used in the laboratory experiments is presented, and the irradiational facility and experimental procedures are described. The results obtained in the conducted experiments are discussed. It is found that there is as yet no basis in laboratory experiments for inferring that perceptible UV photodehydration of FeOOH polymorphs will occur naturally on the surface of Mars on a time scale of at least 10-100 years.

Morris, R. V.↗

NASA NTRS1982

Using known map category marginal frequencies to improve estimates of thematic map accuracy

By means of two simple sampling plans suggested in the accuracy-assessment literature, it is shown how one can use knowledge of map-category relative sizes to improve estimates of various probabilities. The fact that maximum likelihood estimates of cell probabilities for the simple random sampling and map category-stratified sampling were identical has permitted a unified treatment of the contingency-table analysis. A rigorous analysis of the effect of sampling independently within map categories is made possible by results for the stratified case. It is noted that such matters as optimal sample size selection for the achievement of a desired level of precision in various estimators are irrelevant, since the estimators derived are valid irrespective of how sample sizes are chosen.

Card, D. H.↗

NASA NTRS1982

Study of sensor spectral responses and data processing algorithms and architectures for onboard feature identification

A computational model of the deterministic and stochastic processes involved in remote sensing is used to study spectral feature identification techniques for real-time onboard processing of data acquired with advanced earth-resources sensors. Preliminary results indicate that: Narrow spectral responses are advantageous; signal normalization improves mean-square distance (MSD) classification accuracy but tends to degrade maximum-likelihood (MLH) classification accuracy; and MSD classification of normalized signals performs better than the computationally more complex MLH classification when imaging conditions change appreciably from those conditions during which reference data were acquired. The results also indicate that autonomous categorization of TM signals into vegetation, bare land, water, snow and clouds can be accomplished with adequate reliability for many applications over a reasonably wide range of imaging conditions. However, further analysis is required to develop computationally efficient boundary approximation algorithms for such categorization.

Huck, F. O.↗

NASA NTRS1982

Clarification of confirmation in the FACE-2 experiment

Definitions of the data acquisition and interpretation goals which were sought in the Florida Area Cumulus Experiment (FACE) phase-II experiment as confirmation of results from FACE-I are presented. The FACE-1 trials in cloud seeding to increase rainfall were conducted in 1970, '71, '73, '75, and '76 and phase II proceeded from June 1978-August 1980. The data from the second set were to be treated with a block randomization scheme using the mean vector wind speed and direction and superposition of rainfall data, considering fixed and floating target clouds. A first level of probability was configured to eliminate cells from further investigation, and then two other levels are included in the analyses, each of continually increasing levels of likelihood. The instances of rainfall with seeding cover periods of either 60 or more or 60 or less seeding flares being ignited.

Woodley, W. L.↗

NASA NTRS1981

Sensitivity tests of two-dimensional model predictions of corridor effects

Future aerospace-vehicle systems, such as supersonic transport fleets, the Space Shuttle (SS), and the Heavy-Lift Launch Vehicle (HLLV) system will inject substantial amounts of pollutants into the stratosphere. It is, therefore, pertinent to ask whether the operation of these systems will lead to deleterious effects in the atmosphere. The current investigation is concerned with the development of criteria to assess the likelihood of a detectable corridor effect being caused by the long-term deposition of pollutants at a single latitude. The sources are assumed to operate continuously and at a uniform rate for periods of many years. It is found that transport by meridional winds and by eddy processes acts to diminish the corridor effect by advecting the pollutants out of the region of injection and by mixing them with the ambient air. Attention is given to the altitude for which a detectable corridor effect can be expected for the hypothetical launching of 400 HLLV's per year for 10 years.

Borucki, W. J.↗

NASA NTRS1982

Total ozone-solar activity relationship

Approximately six years of global ozone monthly mean data from the Nimbus 4 BUV instrument are compared with monthly values of solar activity using 10.7-cm flux, F(10.7), as a parameter. Several techniques are explored in calculating the correlation between the two data sets, and all are found to yield relatively high correlations, ranging from R = 0.68 for 'raw' monthly means to 0.94 using a six-month running mean for each data set. It is shown, however, that the bulk of the correlation derives from the long-term decreasing trends in both data sets. When the long-term trends are removed, a cross-correlation analysis produces a maximum with no phase shift or with the ozone variations leading the solar variations by one month, thereby reducing the likelihood of a cause and effect relationship on time scales of this order. In view of the current uncertainty in the long-term stability of the BUV instrument and the resulting uncertainty in any long-term trend derived from its data, it is considered unrealistic to draw firm conclusions about a solar cycle influence on total ozone from this satellite data set.

Reber, C. A.↗

NASA NTRS1982

Selected stability and control derivatives from the first three Space Shuttle entries

Stability and control derivative estimates obtained from the first three Space Shuttle entries are presented. The derivative estimates were obtained using the established modified maximum likelihood estimation program (MMLE3). The method of analysis used by the MMLE3 program is reviewed, the Shuttle configuration and data system are described, and the various types of maneuvers analyzed from the three entries are illustrated. Finally, the paper presents selected derivative results and compares them with predictions. Most of the flight-derived estimates agreed fairly well with predictions, considering the lack of experience in these new flight regimes. The most notable exception was the aerodynamic interference caused by firing the reaction control jets in the atmosphere. The flight results showed this interference to be considerably smaller than predicted.

Maine, R. E.↗

NASA NTRS1982

Stability and control flight test results of the space transportation system's orbiter

Flight testing of the Space Shuttle Orbiter is in progress and current results of the post-flight aerodynamic analyses are discussed. The purpose of these analyses is to reduce the pre-flight aerodynamic uncertainties, thereby leading to operational certification of the Orbiter flight envelope relative to the integrated airframe and flight control system. Primary data reduction is accomplished with a well documented maximum likelihood system identification techniques.

Culp, M. A.↗

NASA NTRS1982

Flight-determined correction terms for angle of attack and sideslip

The effects of local flow, upwash, and sidewash on angle of attack and sideslip (measured with boom-mounted vanes) were determined for subsonic, transonic, and supersonic flight using a maximum likelihood estimator. The correction terms accounting for these effects were determined using a series of maneuvers flown at a large number of flight conditions in both augmented and unaugmented control modes. The correction terms provide improved angle-of-attack and sideslip values for use in the estimation of stability and control derivatives. In addition to detailing the procedure used to determine these correction terms, this paper discusses various effects, such as those related to Mach number, on the correction terms. The use of maneuvers flown in augmented and unaugmented control modes is also discussed.

Shafer, M. F.↗

NASA NTRS1982

Self-tuning regulator design for adaptive control of aircraft wing/store flutter

The application of the self-tuning regulator concept to adaptively control aircraft wing/store flutter instability is described. A simple design based on a reduced-order aircraft model has been successfully tested on a high-order simulation of an advanced aircraft, and performance was found to be comparable to another design using on-line maximum likelihood identification of plant parameters. The main advantage of the self-tuning regulator is its simplicity, while the main disadvantage is the inadequacy of prior performance guarantees.

Johnson, T. L.↗

NASA NTRS1981

Computer-based classification accuracy due to the spatial resolution using per-point versus per-field classification techniques

Data sets simulating three different spatial resolutions (SR's) are computed from data with a 15-m nominal SR that were obtained with NASA's Thermatic Mapper Simulator from an altitude of about 6 km. The classification accuracies (CA's) achieved with the data of each of the four different SR's using a per-point Gaussian maximum likelihood classifier (GMLC) are intercompared. The CA's obtained using simulated 30-m SR data with the per-point GMLC are compared with the CA's achieved with a per-field classifier. It is found that: (1) the use of successively higher SR data resulted in lower overall CA's for classifications with the per-point GMLC, especially in cover classes associated with relatively higher spectral variability across adjacent pixels; (2) higher CA's were achieved using the per-field classifier with 30-m SR data than were achieved with the per-point GMLC; and (3) the largest increases in CA's were achieved with the per-field classifier in cover classes associated with relatively high levels of spectral variability across adjacent pixels.

Latty, R. S.↗

NASA NTRS1982

Modeling methodology for MLS range navigation system errors using flight test data

Flight test data was used to develop a methodology for modeling MLS range navigation system errors. The data used corresponded to the constant velocity and glideslope approach segment of a helicopter landing trajectory. The MLS range measurement was assumed to consist of low frequency and random high frequency components. The random high frequency component was extracted from the MLS range measurements. This was done by appropriate filtering of the range residual generated from a linearization of the range profile for the final approach segment. This range navigation system error was then modeled as an autoregressive moving average (ARMA) process. Maximum likelihood techniques were used to identify the parameters of the ARMA process.

Karmali, M. S.↗