Development of an impulse ice-radar for the use of thickness measurements of mountain glaciers

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We have developed a novel ice-penetrating radar system that can be carried on a backpack. Including batteries for a three-hour continuous measurement, the total weight is 13 kg. In addition, it operates reliably down to -25°C, has a low power consumption of 24 W, and is semi-waterproof. The system has a built-in-one controller with a high-brightness display for reading data quickly, a receiver with 12-bit digitizing, and a 1-kV pulse transmitter with time variance of the pulse amplitude of less than 0.2%. The optical communications between components provides low-noise data acquisition and allows synchronizing of the pulse transmission with sampling. Measurements with this system successfully illustrate 300-m deep bed topography of Athabasca Glacier, Canada, in summers 2001 and 2002.To complement a technique to detect internal structures of seasonal snow-covers and glacier firn with ground-penetrating radar (GPR), we carried out calibration experiments and an observation of winter snow-cover (5.7 m thick dry snow with numerous ice layers) with an 800-MHz GPR. In particular, we aimed to discriminate periodic noise from radar echoes, which is inherent in GPR, and to obtain a relationship between the observed reflection strength and the magnitude of density contrasts. Experiments were made in the open space to evaluate noise levels and receiver characteristics of this system. Based on these, we removed noise from radar echoes in the snow-cover observation. We recognized numerous marked echoes in a noise-free radargram. Depths of these echoes coincided roughly with those of large density contrasts observed in the snow-pit. Thus, we argue that the echoes correspond to thin ice layers. Furthermore, the minimum density contrasts to be detected by this GPR are found to vary from about 100 to 250 kg m"3 with the depth from 1 to 6 m in the seasonal snow-cover.