We have developed a miniature high-power impulse transmitter for radio-echo sounding of glaciers. It features two synchronous second break-down pulse generators operating in a differential configuration. Specifications include bipolar 550 V pulses having rise times less than 2 ns, 512 Hz repetition rate, 180 mA at 10-14 V d.c. operating power, 5 mA standby current and maximum dimension of 12 cm. Because of its small size and low power consumption, the transmitter is suitable for back-portable systems and for towed arrays. The transmitter first saw service in 1990 on Trapridge Glacier, Yukon Territory. Subsequent copies have been used on Agassiz Ice Cap, Northwest Territories, Bering Glacier, Alaska and elsewhere. To date, the maximum ice thickness measured using this transmitter is 825 m, on temperate Bering Glacier.

More than 2000 line-kilometres of ice were sounded in 1981 using an 840 MHz pulsed radar system. The surveyed regions include Mt. Oxford ice cap, Disraeli Glacier, Milne Glacier, Ward Hunt Ice Shelf, and Milne Ice Shelf in northern Ellesmere Island, Arctic Canada. The maximum ice thickness that was reliably recorded was 750 m for Milne Glacier. In addition to ice thickness interpretation, the power reflection coefficient (PRC) and propagation loss rate were estimated from the data. Measured basal PRC's differ for ice shelves, floating glaciers, and grounded glaciers. Spatial variations of PRC have been used to infer a composite structure for the ice shelves. Ward Hunt Ice Shelf proved difficult to sound, probably because of its known saline and bxackish chemistly. Excellent results were obtained for Milne Ice Shelf and its depth was found to average roughly 70 m, in places attaining 100 m. Bottom-side crevasses were observed within Milne Ice Shelf. The characteristic ridge and trough topography of the ice shelf surface has little or no bottom-side expression.Des sondages sur plus de 2000 lignes-kilomktres de glace ont CtC effectuCs en 1981 par impulsion radar de 840 MHz. L'acquisition des donnCes couvre les regions de la calotte glaciaire Mt. Oxford, du glacier Disraeli, du glacier Milne, de la plate-forme de glace Ward Hunt, et de la plate-forme de glace Milne dans la partie nord de l'ile Ellesmere, dans 1'Arctique canadien. L'Cpaisseur maximale de la glace qui a kt6 enregistke avec prkcision Ctait de 750 m pour le glacier Milne. En plus de I'interprCtation de I'Cpaisseur de la glace, ces donnCes ont permis d'kvaluer le coefficient du pouvoir de reflexion (CPR) et la fiuction du taux de propagation. Les valeurs mesurCes des CPR different selon qu'il s'agit de plates-forrnes de glace, de glaciers flottants ou de glaciers ancks au sol. Les variations spatiales des CPR ont kt6 utilisCes pour Claborer une structure composite des plates-fonnes de glace. La plate-forme de glace Ward Hunt s'est avCke difficile a sonder, probablement B cause de la pksence connue de sel et d'une chimie saumstre. Des rCsultats excellents ont Ct C obtenus pour la plate-forme Milne et sa profondeur correspond en moyenne a 70 m, a certains endroits elle atteint 100 m. Des crevasses 1atCrales de fond ont CtC observCes t i I'intCrieur de la plate-forme de glace Milne. La crete et la topographie en creux caractkristiques de la surface de la plate-forme de glace ne sont pas, ou seulement peu, exprimkes par la pksence de crevasses laterales de fond.[Traduit par la rewe]Can. J. Earth Sci. 25, 95-105 (1988)

ABSTRACT. We have developed a miniature high-power impulse transmitter for radio-echo sounding of glaciers. It features two synchronous second break-down pulse generators operating in a differential configuration. Specifications include bipolar 550 V pulses having rise times less than 2 ns, 512 Hz repetition rate, 180 mA at 10-14 V d .c. operating power, 5 mA standby current and maximum dimension of 12 cm. Because of its small size and low power consumption, the transmitter is suitable for back-portable systems and for towed arrays. The transmitter first saw service in 1990 on Trapridge Glacier, Yukon Territory. Subsequent copies have been used on Agassiz Ice Cap, Northwest Territories, Bering Glacier, Alaska and elsewhere. To date, the maximum ice thickness measured using this transmitter is 825 m, on temperate Bering Glacier.

We have constructed a back-portable, impulse radar instrument that weighs roughly 12 kg, can be powered by dry cells, and records and stores data digitally. The radar is controlled by an on-board, purpose-built microcomputer that ensures simple field operation, facilitates modifications, and allows unattended operation when investigating time-varying targets. The transmitting unit is triggered from the receiver via an optical link and generates an electromagnetic wavelet by discharging two high-voltage capacitors through back-to-back silicon-controlled rectifiers into a resistively loaded dipole antenna. Successful field operations carried out during the summers of 1986 and 1987 include depth profiling, as well as studies of englacial and subglacial targets, on several temperate and sub-polar glaciers.

We describe an 840 MHz pulsed radar system developed for airborne sounding of polar glaciers and ice caps. The system performance (ratio of transmitter power to minimum detectable signal) is 126 dB. A sampling time base converts the received signal to audio frequencies, and data are recorded in analogue form on magnetic tape. Computer-enhanced time sections for a glacier and an ice shelf are presented as examples.