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  • Other Sources  (11)
  • OCEANOGRAPHY  (4)
  • NUMERICAL ANALYSIS  (3)
  • MACHINERY  (2)
  • PHYSICS (GENERAL)  (1)
  • SPACECRAFT PROPULSION AND POWER  (1)
  • 1985-1989  (11)
  • 1989  (8)
  • 1987  (3)
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  • Other Sources  (11)
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  • 1985-1989  (11)
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  • 1
    Publication Date: 2011-08-19
    Description: An interferometric radar altimeter is proposed to provide wide-swath high-resolution ocean topography. Several system design issues of such an interferometric altimeter are presented. Tradeoffs between processing of the interferometric signal using the so-called amplitude approach and the so-called phase approach are shown. The systematic errors associated with uncertainties in the interferometer baseline and the attitude of interferometer orientation are also discussed. Described is an approach using the measurements at orbit cross-over regions, together with the topography measurements from a traditional nadir-looking altimeter that are not contaminated by the baseline and attitude noises. Preliminary simulation results show that such an approach can generate an acceptable error level if the ocean surface does not change appreciably between the observations.
    Keywords: OCEANOGRAPHY
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  • 2
    Publication Date: 2011-08-19
    Description: The paper reports on an on-going effort at the JPL to estimate the accuracy of ocean state parameters which have been obtained from the specular point probability density function (pdf) of the ocean surface. This pdf is obtained by the deconvolution of the return waveform of oceanographic altimeters such as Seasat, Geosat, or Topex.
    Keywords: OCEANOGRAPHY
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  • 3
    Publication Date: 2011-08-19
    Description: A new method of calculating the electric field scattered from two-dimensional conducting rough surfaces is presented. This method uses the operator conjugate gradients technique and the extended boundary condition equation. This avoids the build-up of round-off errors encountered in the inversion of large matrices. It also avoids the singularities of the integral kernels usually encountered in the method of moments. Techniques for improving the rate of convergence by applying physical constraints are discussed. This method is presently being used to calculate the polarization signatures from simulated ocean-like surfaces.
    Keywords: OCEANOGRAPHY
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  • 4
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    Publication Date: 2011-08-19
    Description: The three most successful models for describing scattering from random rough surfaces are the Kirchhoff approximation (KA), the small-perturbation method (SPM), and the two-scale-roughness (or composite roughness) surface-scattering (TSR) models. In this paper it is shown how these three models can be derived rigorously from one perturbation expansion based on the extinction theorem for scalar waves scattering from perfectly rigid surface. It is also shown how corrections to the KA proportional to the surface curvature and higher-order derivatives may be obtained. Using these results, the scattering cross section is derived for various surface models.
    Keywords: PHYSICS (GENERAL)
    Type: Radio Science (ISSN 0048-6604); 24; 681-693
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  • 5
    Publication Date: 2013-08-31
    Description: The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.
    Keywords: NUMERICAL ANALYSIS
    Type: Proceedings of the 3rd Annual Conference on Aerospace Computational Control, Volume 1; p 26-4
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  • 6
    Publication Date: 2013-08-31
    Description: A recently developed spatial operator algebra, useful for modeling, control, and trajectory design of manipulators is discussed. The elements of this algebra are linear operators whose domain and range spaces consist of forces, moments, velocities, and accelerations. The effect of these operators is equivalent to a spatial recursion along the span of a manipulator. Inversion of operators can be efficiently obtained via techniques of recursive filtering and smoothing. The operator algebra provides a high level framework for describing the dynamic and kinematic behavior of a manipulator and control and trajectory design algorithms. The interpretation of expressions within the algebraic framework leads to enhanced conceptual and physical understanding of manipulator dynamics and kinematics. Furthermore, implementable recursive algorithms can be immediately derived from the abstract operator expressions by inspection. Thus, the transition from an abstract problem formulation and solution to the detailed mechanizaton of specific algorithms is greatly simplified. The analytical formulation of the operator algebra, as well as its implementation in the Ada programming language are discussed.
    Keywords: NUMERICAL ANALYSIS
    Type: Proceedings of the NASA Conference on Space Telerobotics, Volume 5; p 193-204
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  • 7
    Publication Date: 2011-08-19
    Description: An evaluation of the deconvolution method for estimating ocean surface parameters from ocean altimeter waveforms is presented. It is shown that this method presents a fast, accurate way of determining the ocean surface parameters from noisy altimeter data. Three parameters may be estimated by using this method, including the altimeter-height error, the ocean-surface standard deviation, and the ocean-surface skewness. By means of a Monte Carlo experiment, an 'optimum' deconvolution algorithm and the accuracies with which the above parameters may be estimated using this algorithm are determined. Then the influence of instrument effects, such as errors in calibration and pointing-angle estimation, on the estimated parameters is examined. Finally, the deconvolution algorithm is used to estimate height and ocean-surface parameters from Seasat data.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 9761-977
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  • 8
    Publication Date: 2019-07-12
    Description: Set of three reports describes work on Protoflight Manipulator Assembly (PFMA). "Performance Characteristics of Protoflight Manipulator Assembly" presents parameters of PFMA after refurbishment of operating components. "End Effector and Task Board Development for the Protoflight Manipulator Assembly" describes special tools and adaptations allowing PFMA to be used for servicing equipment. "Modular Software Development for the Protoflight Manipulator Assembly" documents interface and control software for PFMA.
    Keywords: MACHINERY
    Type: MFS-27067 , NASA Tech Briefs (ISSN 0145-319X); 13; 9; P. 97
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  • 9
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    Publication Date: 2019-07-12
    Description: Forward and inverse dynamics solved using Kalman filtering and Bryson-Frazier smoothing. Dynamics of serial-link robot arm solved by using recursive techniques from linear filtering and smoothing theory. Solutions of dynamical equations give forces, moments, and accelerations at joints between links, and multilink inertia matrix and its inverse. Theoretical developments lay foundation for use of filtering and smoothing techniques in design of robot controls.
    Keywords: MACHINERY
    Type: NPO-17040 , NASA Tech Briefs (ISSN 0145-319X); 11; 7; P. 85
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  • 10
    Publication Date: 2019-07-13
    Description: A spatial operator algebra for modeling the control and trajectory design of manipulation is discussed, with emphasis on its analytical formulation and implementation in the Ada programming language. The elements of this algebra are linear operators whose domain and range spaces consist of forces, moments, velocities, and accelerations. The effect of these operators is equivalent to a spatial recursion along the span of the manipulator. Inversion is obtained using techniques of recursive filtering and smoothing. The operator alegbra provides a high-level framework for describing the dynamic and kinematic behavior of a manipulator and control and trajectory design algorithms. Implementable recursive algorithms can be immediately derived from the abstract operator expressions by inspection, thus greatly simplifying the transition from an abstract problem formulation and solution to the detailed mechanization of a specific algorithm.
    Keywords: NUMERICAL ANALYSIS
    Type: 1989 IEEE International Conference on Robotics and Automation; May 14, 1989 - May 19, 1989; Scottsdale, AZ; United States
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