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  • 1
    ISSN: 1616-7228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Summary From 22 September to 4 October 1983 surface currents, in front of Sylt, were measured by means of two radar sites. The sampling rate varied between 1/2 and 2 hours. The 2-dimensional current velocities refer to a grid system with resolution of 3 km and mean extend of 30 km×30 km. Time series are constructed with respect to different grid points. Their tidal- and wind-driven parts are estimated by least-squares-methods. Beside the dominant semi-diurnal tide there is also a strong quarter-diurnal tide. A linear dependence is found between the velocities of current and wind with a ratio of 0.018 and 0.012 for the northern and eastern component, respectively. The semi-diurnal tidal ellipses are clearly dependent on the topography.
    Abstract: Résumé Des mesures de courants de surface ont été effectuées au large de Sylt à l'aide de deux stations Radar du 22 septembre au 4 octobre 1983. L'intervalle de temps entre les mesures successives variait entre 1/2 heure et 2 heures. Les vitesses bidimensionnelles du courant sont rapportées à un réseau de 3 km de résolution et d'une étendue moyenne de 30 km×30 km. On établit des séries temporelles pour les différents points du réseau. Leurs parts de mouvement relevant de la marée et du vent sont calculées par la méthode des moindres carrés. Il existe une forte marée quart-diurne à côté de la marée dominante semidiurne. Une relation linéaire est trouvée entre la vitesse du courant et celle du vent avec un facteur de proportionnalité de 0,018 et 0,012 respectivement pour les composantes nord et est. Les ellipses du courant relatives à la marée semidiurne dépendent nettement de la topographie.
    Notes: Zusammenfassung Vom 22. September bis zum 4. Oktober 1983 wurden mit zwei Radarstationen von Sylt aus Oberflächenströmungen gemessen. Die zeitliche Abtastrate der 274 Messungen variiert zwischen 1/2 und 2 Studen. Die 2 dimensionalen Strömungsgeschwindigkeiten liegen in einem Gitternetz mit 3 km Auflösung und einer mittleren Ausdehnung von 30 km×30 km vor. Für die einzelnen Gitterpunkte werden Zeitserien erstellt, deren gezeiten- und windgetriebene Anteile mit der Methode der kleinsten Quadrate bestimmt werden. Neben der dominanten halbtägigen Gezeit wird ein starker vierteltägiger Anteil gefunden. Der Zusammenhang zwischen Strömungs- und Windgeschwindigkeit erweist sich als linear mit einem Proportionalitäts-faktor von 0,018 für die Nord- und 0,012 für die Ostkomponente. Die Gezeitenellipsen der halbtägigen Gezeit zeigen eine deutliche Abhängigkeit von der Topographie.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Ocean dynamics 44 (1991), S. 35-49 
    ISSN: 1616-7228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Summary Following a brief introduction into the GPS-System results are presented and discussed of tests of accuracy of one particular instrument. Tests were made from both a fixed position and on board ship. Depending on the geometry between the satellites an accuracy of 18 m in position and of 2 sm/s in velocity can be obtained (at σ andHDOP≤7). On the basis of measurements on board ship, the dynamic resolution is shown to be better than one meter, and both roll and pitch can be resolved within this range. The survey was conducted prior to activation of an intentional degradation of the system by “Selective Availability”.
    Notes: Zusammenfassung Nach einer kurzen Einführung werden die Ergebnisse einer Genauigkeitsuntersuchung des GPS-Systems gezeigt und diskutiert. Die Messungen wurden sowohl an einem festen Standort als auch an Bord eines Schiffes durchgeführt. Es zeigt sich, daß abhängig von der geometrischen Stellung der Satelliten zueinander eine Genauigkeit der Position von 18 Metern und eine Genauigkeit der angezeigten Geschwindigkeit von 2 cm/s erreicht wird (für σ undHDOP≤7). Anhand der Schiffsmessungen wird gezeigt, daß die dynamische Auflösung besser als ein Meter ist, und sich Roll- und Stampfbewegungen in diesem Bereich erfassen lassen. Die Untersuchung bezieht sich auf Messungen vor dem Aktivieren der Verschlechterung des Systems durch “Selective Availability”.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Ocean dynamics 36 (1983), S. 81-96 
    ISSN: 1616-7228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Mit einer HF-Radarstation wurden im Dezember 1982 vor Sylt Oberflächenströmungen gemessen. Dabei wurden zwei Trägerfrequenzen (25,25 MHz und 29,85 MHz) hinsichtlich ihrer Eignung getestet. Radiale (eindimensionale) Strömungen, in verschiedenen Entfernungen und Richtungen von dem Radar, wurden über 70 Stunden stündlich registriert. Aus diesen Zeitserien wird der gezeiten- und windgetriebene Anteil bestimmt. Unter der Annahme eines homogenen Strömungsfeldes werden Ellipsen für die halbtägige Gezeit konstruiert und mit Gezeitenströmungen verglichen, die im “Atlas der Gezeitenströme in der Deutschen Bucht” (Deutsches Hydrographisches Institut [1983]) dokumentiert sind.
    Abstract: Résumé En décembre 1982, des mesures de courants de surface furent effectuées au moyen d'une station Radar HF devant l'île allemande de «Sylt» dans la Mer du Nord. Lors des essais de mise en oeuvre deux porteuses de fréquences 25,25 MHz et 29,85 MHz furent testées. Des séries chronologiques 70 heures de durée comprenant des courants radiaux prélevés toutes les heures à différentes distances et dans diverses directions à partir du radar, sont analysées dans le but de déterminer les parts de la marée et du vent. En supposant un champ de courant homogène, des ellipses de marées semi-diurnes sont calculées et comparées aux données de l'«Atlas der Gezeitenströme in der Deutschen Bucht» (Deutsches Hydrographisches Institut [1983]).
    Notes: Summary In December 1982, surface current measurements by means of an HF radar station were carried out from the Federal German island of Sylt in the North Sea. Two carrier frequencies (25.25 MHz and 29.85 MHz) were tested with respect to their applicability. Hourly sampled 70-hours time series of (1-dimensional) radial currents at different distances and directions from the radar are analyzed with the objective of determining the tidal and wind-driven parts. Assuming a homogeneous current field, semidiurnal tidal ellipses are synthesized and compared with currents, as documented in the “Atlas der Gezeitenströme in der Deutschen Bucht” (Deutsches Hydrographisches Institut [1983]).
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  • 4
    Publication Date: 2010-08-01
    Description: The evolution of a submesoscale anticyclonic vortex was observed by high-frequency Doppler radio current meters and satellite radiometers. The vortex formed between two large cyclones to the southwest of Oahu, Hawaii. The radius of the core was ∼15 km; the azimuthal velocity reached 35 cm s−1; and the surface vorticity remained below −f for 9 days, reaching an extremum of −1.7f. The flow was ageostrophic near the center and around the periphery of the vortex. The initial growth may have been driven by negative wind stress curl in the lee of Oahu. The vortex was prone to inertial, symmetric, and anticyclonic ageostrophic instabilities, but the temporal evolution of radial profiles of vorticity was inconsistent with angular momentum redistribution by inertial instability. A tongue of surface water 0.7°C warmer became entrained northward between the vortex and the colder cyclone to the west. As the vortex strengthened, a 0.14°C km−1 front formed along the eastern flank of the tongue. The sea surface temperature gradient remained weaker on the western flank. The flow was anticyclonic (−0.4f ) and divergent (0.1f ) on the warm side of the front but cyclonic (0.6f ) and convergent (−0.2f ) on the cold side. This suggests ageostrophic cross-frontal circulations maintaining alongfront thermal wind balance in the presence of large-scale strain σ. Surface divergence δ was proportional to vorticity ζ during the 3-day frontogenesis: δ ∼ −(σ/f )ζ. This is consistent with a semigeostrophic model of a front confined to a surface layer of zero potential vorticity.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2010-10-01
    Description: Short-wavelength (L ∼ 100 km) Rossby waves with an eastward zonal phase velocity were observed by high-frequency radio Doppler current meters and moored ADCPs west of Oahu, Hawaii, during spring 2003. They had Rossby numbers Ro = |ζ/f| = O(1), periods of 12–15 days, and phase speeds of 8–9 cm s−1, and they were surface trapped with vertical e-folding scales of 30–170 m. They transferred horizontal kinetic energy to the background flow of a mesoscale cyclone lying 160–190 km west of Oahu, revealed by altimetry. The waves approximately satisfied the dispersion relation of vortex Rossby waves propagating through the radial gradient of potential vorticity associated with the cyclone. Vertical shear of the background currents may also affect wave propagation. Theoretical studies have shown that vortex Rossby waves provide a mechanism by which perturbed vortices axisymmetrize and strengthen and may be important to the dynamics of oceanic vortices.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
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  • 6
    Publication Date: 1989-01-01
    Print ISSN: 0280-6495
    Electronic ISSN: 1600-0870
    Topics: Geography , Geosciences , Physics
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  • 7
    Publication Date: 1989-03-01
    Print ISSN: 0280-6495
    Electronic ISSN: 1600-0870
    Topics: Geography , Geosciences , Physics
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  • 8
    Publication Date: 2018-09-16
    Description: Land-based, high-frequency (HF) surface wave radar has the unique capability of monitoring coastal surface parameters, such as current, waves, and wind, up to 200 km off the coast. The Doppler spectrum of the backscattered radar signal is characterized by two strong peaks that are caused by the Bragg-resonant scattering from the ocean surface. The wavelength of Bragg resonant waves is exactly half the radio wavelength (grazing incidence), and these waves are located at the higher frequency part of the wave spectral distribution. When HF radar operates at higher frequencies, the resonant waves are relatively shorter waves, which are more sensitive to a change in wind direction, and they rapidly respond to local wind excitation and a change in wind direction. When the radar operates at lower frequencies, the corresponding resonant waves are relatively longer and take longer time to respond to a change in wind direction due to the progress of wave growth from short waves to long waves. For the wind inversion from HF radar backscatter signals, the accuracy of wind measurement is also relevant to radar frequency. In this paper, a pattern-fitting method for extracting wind direction by estimating the wave spreading parameter is presented, and a comparison of the pattern-fitting method and a conventional method is given as well, which concludes that the pattern-fitting method presents better results than the conventional method. In order to analyze the wind direction inversion from radar backscatter signals under different wind conditions and at different radar frequencies, two radar experiments accomplished in Norway and Italy are introduced, and the results of wind direction inversion are presented. In the two experiments, the radar worked at 27.68 MHz and 12 MHz, respectively, and the wind conditions at the sea surface were quite different. In the experiment in Norway, 67.4% of the wind records were higher than 5 m/s, while, in the experiment in Italy, only 18.9% of the wind records were higher than 5 m/s. All these factors affect the accuracy of wind direction inversion. The paper analyzes the radar data and draws a conclusion on the influencing factor of wind direction inversion.
    Electronic ISSN: 2072-4292
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 9
    Publication Date: 1983-05-01
    Print ISSN: 0012-0308
    Electronic ISSN: 1616-7228
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
    Publication Date: 1991-01-01
    Print ISSN: 0012-0308
    Electronic ISSN: 1616-7228
    Topics: Geosciences , Physics
    Published by Springer
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