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  • COMMUNICATIONS AND RADAR  (127)
  • CYBERNETICS  (113)
  • 2000-2004
  • 1990-1994  (240)
  • 1
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    Interferometric tracking system for the tracking and data relay satellite (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This report documents construction and testing of the Interferometric Tracking System project developed under the NASA SBIR contract NAS5-30313. Manuals describing the software and hardware, respectively entitled: 'Field Station Guide to Operations' and 'Field Station Hardware Manual' are included as part of this final report. The objective of this contract was to design, build, and operate a system of three ground stations using Very Long Baseline Interferometry techniques to measure the TDRS orbit. The ground stations receive signals from normal satellite traffic, store these signals in co-located computers, and transmit the information via phone lines to a central processing site which correlates the signals to determine relative time delays. Measurements from another satellite besides TDRS are used to determine clock offsets. A series of such measurements will ultimately be employed to derive the orbital parameters, yielding positions accurate to within 50 meters or possibly better.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-193274 , NAS 1.26:193274
    Format: application/pdf
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  • 2
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    Analysis of the eastern range multiplexed fiber optic IRIG B120 distribution system (1993)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A study was conducted to assess the effects of transmitting a precision clock synchronization signal over a commercial multiplexed fiber optic communication system. This study is an evaluation of the distortion and jitter introduced into the signal by this type of transmission system. An analysis comparing signal quality at the multiplexing and demultiplexing ends of the fiber optic communication system shows that the amplitude and phase distortion added to the clock synchronization signal by the transmission system is minimal.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Goddard Space Flight Center, The 24th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 375-384
    Format: text
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  • 3
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    Continuous motion using task-directed stereo vision (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The performance of autonomous mobile robots performing complex navigation tasks can be dramatically improved by directing expensive sensing and planning in service of the task. The task-direction algorithms can be quite simple. In this paper we describe a simple task-directed vision system which has been implemented on a real outdoor robot which navigates using stereo vision. While the performance of this particular robot was improved by task-directed vision, the performance of task-directed vision in general is influenced in complex ways by many factors. We briefly discuss some of these, and present some initial simulated results.
    Keywords: CYBERNETICS
    Type: In: Sensor fusion IV: Control paradigms and data structures; Proceedings of the Meeting, Boston, MA, Nov. 12-15, 1991 (A93-49438 21-63); p. 294-298.
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  • 4
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    Maximum entropy method applied to deblurring images on a MasPar MP-1 computer (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A statistical inference method based on the principle of maximum entropy is developed for the purpose of enhancing and restoring satellite images. The proposed maximum entropy image restoration method is shown to overcome the difficulties associated with image restoration and provide the smoothest and most appropriate solution consistent with the measured data. An implementation of the method on the MP-1 computer is described, and results of tests on simulated data are presented.
    Keywords: CYBERNETICS
    Type: In: Image understanding in the '90s: Building systems that work; Proceedings of the Meeting, McLean, VA, Oct. 18, 19, 1990 (A93-20261 06-63); p. 138-146.
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  • 5
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    Decorrelation in interferometric radar echoes (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A radar interferometric technique for topographic mapping of surfaces promises a high resolution, globally consistent approach to generation of digital elevation models. One implementation approach, that of utilizing a single SAR system in a nearly repeating orbit, is attractive not only for cost and complexity reasons but also in that it permits inference of changes in the surface over the orbit repeat cycle from the correlation properties of the radar echoes. The various sources contributing to the echo correlation statistics are characterized, and the term which most closely describes surficial change is isolated. There is decorrelation increasing with time, but digital terrain model generation remains feasible.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 5; p. 950-959.
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  • 6
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    Techniques in processing multi-frequency multi-polarization spaceborne SAR data (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: This paper presents the algorithm design of the SIR-C ground data processor, with emphasis on the unique elements involved in the production of registered multifrequency polarimetric data products. A quick-look processing algorithm used for generation of low-resolution browse image products and estimation of echo signal parameters is also presented. Specifically the discussion covers: (1) azimuth reference function generation to produce registered polarimetric imagery; (2) geometric rectification to accommondate cross-track and along-track Doppler drifts; (3) multilook filtering designed to generate output imagery with a uniform resolution; and (4) efficient coding to compress the polarimetric image data for distribution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: European Transactions on Telecommunications and Related Technologies (ISSN 1120-3862); 2; 6, No
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  • 7
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    Adaptive structures for precision controlled large space systems (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The development of adaptive structural systems is reviewed and the potential of these systems in meeting some of the requirements for NASA future space missions is demonstrated. Particular attention is given to the characteristics of a viscous damper in the micron displacement regime; the optimal placement of active and passive members into a truss structure; a system identification test using the active members as excitation sources; a concept for deforming a lightweight composite honeycomb optical panel to correct for on-orbit distortions by using piezoelectric actuators attached to the back facesheet; and the results of an active member vibration control experiment in a reduced gravity environment.
    Keywords: CYBERNETICS
    Type: Journal of Intelligent Material Systems and Structures (ISSN 1045-389X); 3; 2, Ap
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  • 8
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    An algorithm to design a multiple-channel communications system (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The authors present a novel algorithm to design a phase-modulated residual carrier communications system for optimum performance. The algorithm has been developed as an aid in the design of two telemetry data channels operating simultaneously with a turn-around ranging signal. The algorithm provides the selection of an optimum subcarrier frequency and modulation indices for minimizing the mutual interferences among the channels to achieve desired link performance margins. The set of modulation indices provided by this algorithm will also achieve an optimum power division between the carrier, the ranging and the high data rate and low data rate channels. Finally, a software program using this algorithm has been developed for use with personal computers. This program provides the computation of the optimum subcarrier frequencies and modulation indices for a standard case that is recommended by the international Consultative Committee for Space Data Systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: GLOBECOM '91 - IEEE Global Telecommunications Conference, Phoenix, AZ, Dec. 2-5, 1991, Conference Record. Vol. 1 (A93-10926 01-32); p. 515-520.
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  • 9
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    Towards a methodology for robust parameter identification (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Consideration is given to the problem of estimating, from experimental data, real parameters for a model with uncertainty in the form of both additive noise and norm-bounded perturbations. Such models frequently arise in robust control theory, and a framework is introduced for the consideration of experimental data in robust control analysis problems. If the analysis tools applied include robust stability tests for real parameter variations (real mu), the framework can be used to address the problem of robust parameter identification. While the techniques discussed can quickly become computationally overwhelming when applied to physical systems and real data, the approach introduces a novel way of looking at the identification problem and may be helpful in arriving at a more tractable methodology.
    Keywords: CYBERNETICS
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  • 10
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    A numerical study of the separation wavenumber in the two-scale scattering approximation (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The choice of the separation wavenumber Kd for the two-scale scattering approximation is examined by the comparison of two-scale calculations with exact numerical solutions using the moment method. It was found that the optimal choice of Kd is near k/2 when attempting to optimize for all incidence angles. When optimizing for specific incidence angles, Kd varied from k/5 at low incidence angles to just below k at higher incidence angles. These numerical results are in rough agreement with previous theoretical derivations of the separation wavenumber.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 28; 271
    Format: text
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