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Systems for Measuring Thickness of Temperate and Polar Ice from the Ground or from the Air

  • Raymond D. Watts (a1) and David L. Wright (a1)

Abstract

Equipment has been designed and tested for ground-based and airborne sounding of temperate glaciers. The transmitter is a free-running pulse generator that uses avalanche-mode transistor breakdown to create high-voltage pulses. The transmit and receive antennas are resistively loaded dipoles; for the airborne system, a twin-lead transmit element and a three-layer coaxial receive element are used on the inboard end of the respective antennas. The sounders are broadband systems; oscilloscopes are used for receivers. The oscilloscope trace is recorded photographically in the ground-based systems. A sampling oscilloscope is used in the airborne system—the sampling process strobes the waveform to audio frequencies so that it can be recorded on magnetic tape. Echoes have been obtained from ice depths of 550 m using the airborne system and about 1 000 m using the ground-based system.

Résumé

On a conçu et essayé un équipement pour sonder des glaciers tempérés depuis un aéronef ou depuis une base au sol. L’émetteur est un générateur libre d’impulsions qui utilise des décharges en forme d’avalanche par transistor pour créer des impulsions à fort voltage. Les antennas émettrices et réceptrices sont des dipoles chargés en résistance. Pour la version aérienne, un élément émetteur à direction jumelée et un récepteur coaxial à trois niveaux sont utilisés sur l’extrémité du bord des antennes respectives. Les sondeurs sont des systèmes à large bande; on utilise des oscilloscopes comme récepteurs. Le signal de l’oscilloscope est enregistré photographiquement dans les appareils basés au sol. Dans la version aérienne, on utilise un oscilloscope à échantillonnage. La procédé par échantillonnage transforme les oscillations en fréquences acoustiques de sorte qu’on peut les enregistrer sur bandes magnétiques. Des échos ont été obtenus depuis des profondeurs de glace de 550 m avec la version aérienne et d’environ 1 000 m avec la version terrestre.

Zusammenfassung

Zur Dickenmessung temperierten Eises von der Oberfläche und aus der Luft wurden neue Geräte entwickelt und erprobt. Der Sender ist ein Impulsgenerator, der zur Erzeugung hochgespannter Impulse eine lawinenartige Transistor-Auslösung benutzt. Die Sende- und Empfangsantennen sind aufgeladene Wider-standsdipole. Für das flugzeuggetragene Systeme sind ein Sendeelement mit Doppelleiter und ein dreiadriges, koaxiales Empfangselement vorgesehen, die am inneren Ende der jeweiligen Antennen sitzen. Die Messung erfolgt mit Breitbandsystemen; an die Empfänger sind Oszilloskope angeschlossen. Die Oszilloskopaufzeichnung wird beim Bodensystem photographisch registriert. Das flugzeuggetragene System benutzt ein Auswahl-Oszilloskop, das die Wellenfront zur Aufzeichnung auf Magnetband in Audiofrequenzen umwandelt. Mit dem flugzeuggetragenen System wurden Reflexionen aus Eistiefen von 550 m erhalten, mit dem Bodensystem solche von etwa 1 000 m.

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References

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Bishop, J. F., and others. 1979.The 1977 Cambridge University expedition to Vatnajökull, Iceland, by Bishop, J. F., Cumming, A.D.G., Ferrari, R. L., Miller, K.J., and Owen, G.. Cambridge, University of Cambridge. Dept. of Engineering. (Special Report 6.)
Ferrari, R. L., and others. 1976, The 1976 Cambridge-Reykjavik Universities expedition to Varnajökull, Iceland, by Ferrari, R. L., Miller, K.J., Owen, G. Cambridge, University of Cambridge. Dept. of Engineering. (Special Report 5.)
Harrison, C. H. 1970. Reconstruction of subglacial relief from radio-echo sounding records. Geophysics, Vol. 35, No. 6, p. 1099115.
Robin, G. de Q. 1974. Radio-echo sounding: glaciological interpretations and applications. Journal of Glaciology, Vol. 15, No. 73, p. 4964.
Sverrisson, M., and others. 1978. Radio-echo equipment for sounding of temperate glaciers, by Sverrisson, M., Jóhanneson, A., and Björnsson, H.. Reykjavík, Science Institute, University of Iceland. (Report RH-78-16.)
Watts, R. D., and England, A. W. 1976. Radio-echo sounding of temperate glaciers: ice properties and sounder design criteria. Journal of Glaciology, Vol. 17, No. 75, p. 3948.
Watts, R, D., and Isherwood, W. 1978. Gravity surveys in glacier-covered regions. Geophysics, Vol. 43, No. 4, p. 81922.

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