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At least 433 records · Page 24

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NASA NTRS1972

A Bayesian model for visual space perception

A model for visual space perception is proposed that contains desirable features in the theories of Gibson and Brunswik. This model is a Bayesian processor of proximal stimuli which contains three important elements: an internal model of the Markov process describing the knowledge of the distal world, the a priori distribution of the state of the Markov process, and an internal model relating state to proximal stimuli. The universality of the model is discussed and it is compared with signal detection theory models. Experimental results of Kinchla are used as a special case.

Curry, R. E.↗

NASA NTRS1973

Cluster Seeking Techniques in Pattern Recognition

A cluster seeking technique is defined as a method of dividing data into subsets, called clusters. These clusters contain data points that are similar to each other and different from the elements of other clusters. Various cluster seeking techniques were broken down into seven categories: (1) probabilistic, (2) signal detection, (3) clustering, (4) clumping, (5) eigenvalue, (6) minimal mode seeking, and (7) miscellaneous. Each category is described and one or more algorithms of that type are presented.

Barr, B. J.↗

NASA NTRS1973

A note on signal enhancement for dual magnetometer systems.

Demonstration of the value of cross-correlation signal enhancement achieved by means of a dual magnetometer system. A unique feature of a dual magnetometer system is, as pointed out by Ness et al. (1971), the opportunity it allows for signal enhancement by using cross-correlation techniques developed in statistical communication theory. Their use is shown to make it possible to overcome the limitations that the intrinsic sensor ambient noise and the measurement-contaminating spacecraft field fluctuations impose upon the signal detection performance of a single magnetometer.

Ness, N. F.↗

NASA NTRS1973

Photon counting with a self-scanned diode array.

A self-scanned diode array may be used as temporary storage for individual photons if enough gain is provided by an image intensifier or electron multiplier to provide a detectable signal from each input event.

Mcnall, J. F.↗

NASA NTRS1973

The radiometer transfer function for the AAFE composite two-frequency radiometer scatterometer

A model was developed for the switching radiometer utilizing a continuous method of calibration. Sources of system degradation were identified and include losses and voltage standing wave ratios in front of the receiver input. After computing the three modes of operation, expressions were developed for the normalized radiometer output, the minimum detectable signal (normalized RMS temperature fluctuation), sensitivity, and accuracy correction factors).

Moore, J. H.↗

NASA NTRS1974

Applications of tunable high energy/pressure pulsed lasers to atmospheric transmission and remote sensing

Atmospheric transmission of high energy C12 O2(16) lasers were improved by pulsed high pressure operation which, due to pressure broadening of laser lines, permits tuning the laser 'off' atmospheric C12 O2(16) absorption lines. Pronounced improvement is shown for horizontal transmission at altitudes above several kilometers, and for vertical transmission through the entire atmosphere. The atmospheric transmission of tuned C12 O2(16) lasers compares favorably with C12 O2(18) isotope lasers and CO lasers. The advantages of tunable, high energy, high pressure pulsed lasers over tunable diode lasers and waveguide lasers, in combining high energies with a large tuning range, are evaluated for certain applications to remote sensing of atmospheric constituents and pollutants. Pulsed operation considerably increases the signal to noise ratio without seriously affecting the high spectral resolution of signal detection obtained with laser heterodyning.

Hess, R. V.↗

NASA NTRS1974

Jupiter emission observed near 1 MHz

Emission from Jupiter has been observed by the IMP-6 spacecraft at 19 frequencies between 600 and 9900 kHz covering the period from April 1971 to October 1972. The Jovian bursts were identified in the IMP-6 data through the phase of the observed modulated signal detected from the spinning dipole antenna. Initial data reduction has isolated 177 events over a span of 500 days. These events persisted over a period between 1 and 60 min. Of these events at least 48 occurred during times in which Jupiter emission was being observed at either 16.7 or 22.2 MHz by ground-based instruments of the Goddard Space Flight Center Jupiter monitoring system. Large bursts were detectable from 9900 kHz down to 600 kHz, while smaller bursts ranged down to 1030 kHz.-

Brown, L. W.↗

NASA NTRS1974

AAFE man-made noise experiment project. Volume 3: Appendices

Management and operational considerations involved in the project to measure man-made electromagnetic noise at earth orbital altitudes are discussed. The subjects considered are: (1) launch and orbit of the Scout D vehicles, (2) experiment management, (3) receiver scanning considerations, (4) data handling, and (5) threshold measurements. The storage requirements for a high resolution, complete data storage library are defined. Mathematical models of signal detection probability are developed.

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NASA NTRS1975

Saturn radio emission near 1 MHz

Emission from the direction of the planet Saturn was observed by the IMP-6 spacecraft at 15 frequencies between 375 and 2200 kHz during the period April 1971 to October 1972. The Saturnian radio bursts were identified in the IMP-6 data through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. Initial data reduction has isolated approximately 12 storms whose occurrence corresponded to times in which the spacecraft had an unobstructed view in the direction of Saturn. These events persisted over periods between one and ten minutes. Over the span of 500 days of data another 10 to 20 Saturnian events may exist, but positive identification is confused by the presence of terrestrial noise as well as a geometric ambiguity with Jupiter. A power spectral analysis of the storm occurrence times indicates a weak periodicity at 10h 30m + or - 5m at some of the observing frequencies. The spectral character of the radiation was found analogous to that of Jupiter.

Brown, L. W.↗

NASA NTRS1973

Proceedings of the 9th Annual Conference on Manual Control

Papers are reported which were presented at the conference in the areas of displays, ride qualities and handling, driving and psychomotor skills, control, system identification and signal detection, electrophysiological and systems analysis, and modelling.

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NASA NTRS1973

On modeling performance of open-loop mechanisms

A technique is presented for modeling the performance of open-loop mechanisms or systems, where performance is measured by success or failure as a function of the selected target for movement along a constrained trajectory and without corrective feedback. A modification of signal detection theory is used, which normalizes dissimilar data and indicates two independent parameters of performance: (1) discriminability and (2) optimality of the distribution of selected moves. An illustrative application is made to experimental data.

Sheridan, T. B.↗

NASA NTRS1974

Man-systems evaluation of moving base vehicle simulation motion cues

A motion cue investigation program is reported that deals with human factor aspects of high fidelity vehicle simulation. General data on non-visual motion thresholds and specific threshold values are established for use as washout parameters in vehicle simulation. A general purpose similator is used to test the contradictory cue hypothesis that acceleration sensitivity is reduced during a vehicle control task involving visual feedback. The simulator provides varying acceleration levels. The method of forced choice is based on the theory of signal detect ability.

Kirkpatrick, M.↗

NASA NTRS1974

Spectral behavior of Jupiter near 1 MHz

Emission from Jupiter has been observed by the IMP-6 spacecraft at 25 frequencies between 425 and 9900 kHz covering the period April 1971 to October 1972. The Jovian bursts were identified through the phase of the observed modulated signal detected from the spinning dipole antenna. Approximately 500 days of data have been scanned for Jupiter emissions with a positive detection of at least 382 events. The static spectral behavior of the emission has been investigated and can be divided naturally into three types. Type one (normal) shows a high correlation with earth-based observations and follows the same spectral behavior. These bursts are seldom detected much below 1 MHz. The second type (md-frequency) occurs near or below 1 MHz and shows low and high-frequency cutoffs. The emission peak is near 900 kHz with a 3 db bandwidth of approximately 450 kHz. A third type consists of a complex combination of the previous types.

Brown, L. W.↗

NASA NTRS1975

Absolute radiometric calibration of detectors between 200-600 A

A description is given of the experimental methods used in the calibration procedure, taking into account the source of radiant energy, the monochromator, the absolute standard detector, and the transfer standards. The experimental apparatus is discussed. A graph showing the effect of beam motion on the detected signal is presented and a block diagram of the calibration electronic system is provided.

Saloman, E. B.↗

NASA NTRS1976

Integrated source and channel encoded digital communication system design study

The results of several studies Space Shuttle communication system are summarized. These tasks can be divided into the following categories: (1) phase multiplexing for two- and three-channel data transmission, (2) effects of phase noise on the performance of coherent communication links, (3) analysis of command system performance, (4) error correcting code tradeoffs, (5) signal detection and angular search procedure for the shuttle Ku-band communication system, and (6) false lock performance of Costas loop receivers.

Huth, G. K.↗

NASA NTRS1976

Selective attention and the auditory vertex potential. I - Effects of stimulus delivery rate. II - Effects of signal intensity and masking noise

The effects of varying the rate of delivery of dichotic tone pip stimuli on selective attention measured by evoked-potential amplitudes and signal detectability scores were studied. The subjects attended to one channel (ear) of tones, ignored the other, and pressed a button whenever occasional targets - tones of a slightly higher pitch were detected in the attended ear. Under separate conditions, randomized interstimulus intervals were short, medium, and long. Another study compared the effects of attention on the N1 component of the auditory evoked potential for tone pips presented alone and when white noise was added to make the tones barely above detectability threshold in a three-channel listening task. Major conclusions are that (1) N1 is enlarged to stimuli in an attended channel only in the short interstimulus interval condition (averaging 350 msec), (2) N1 and P3 are related to different modes of selective attention, and (3) attention selectivity in multichannel listening task is greater when tones are faint and/or difficult to detect.

Schwent, V. L.↗

NASA NTRS1976

The use of dispersion to eliminate multipath in planetary radio occultations

Occultation geometry is analyzed with a view toward eliminating all multipath resulting from layer effects. It is assumed that the spacecraft moves behind the planet with a constant velocity perpendicular to the direction from the spacecraft to the earth, and that for radio frequencies of 1 to 2 GHz the angle of refraction of a radio ray passing through the ionosphere is so small as to be imperceptible if drawn to scale. It is shown that if a particular amount of dispersion is inserted into the process at any stage prior to signal detection, the frequency vs time curve will be converted to a frequency vs ray asymptote height curve. Because there can be only one mode from any one ray asymptote height in a layered medium, frequency must be a single-valued function of this parameter. The introduction of an appropriate dispersion will therefore eliminate all multipath insofar as it is caused by spherically symmetric planetary layers. The degree of accuracy to be provided in flight and during postflight analysis is discussed.

Croft, T. A.↗

NASA NTRS1977

Satellite-based interference analyzer

System identifies terrestrial sources of radiofrequency interference and measures their frequency spectra and amplitudes. Designed to protect satellite communication networks, system measures entire noise spectrum over selected frequency band and can raster-scan geographical region to locate noise sources. Once interference is analyzed, realistic interference protection ratios are determined and mathematical models for predicting ratio-frequency noise spectra are established. This enhances signal-detection and locates optimum geographical positions and frequency bands for communication equipment.

Varice, H.↗