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

我们开发了一种新型的穿冰雷达系统，可以放在背包里携带。包括三个小时连续测量的电池在内，总重量为13公斤。此外，它的工作可靠性低至-25°C，功耗低至24W，并且是半防水的。该系统具有内置高亮度显示屏的控制器，用于快速读取数据，接收器具有12位数字化，以及脉冲幅度随时间变化小于0.2%的1千伏脉冲发射器。组件之间的光通信提供低噪声数据采集，并允许脉冲传输与采样同步。该系统的测量成功地显示了2001年和2002年夏季加拿大阿萨巴斯卡冰川300m深的海床地形。为了补充用探地雷达(GPR)探测季节性积雪和冰川积雪内部结构的技术，我们进行了定标实验和用800 MHz探地雷达观测冬季积雪(5.7m厚的干雪和大量的冰层)。特别是，我们的目标是区分雷达回波中固有的周期性噪声，并获得观测到的反射强度与密度对比度大小之间的关系。在开放空间进行了实验，以评估该系统的噪声水平和接收器特性。在此基础上，对雪盖观测中的雷达回波进行了去噪处理。我们在无噪声的雷达图中识别出大量明显的回声。这些回声的深度与在雪坑中观察到的大密度对比大致重合。因此，我们认为这些回声对应于薄冰层。此外，该探地雷达探测到的最小密度对比度约为100~250 kg m~(-3)，季节积雪深度为1~6米。

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.