Helicopter-borne ground penetrating radar measurements on the Sørsdal Glacier 2017-2018

Ground penetrating radar (GPR) is an active geophysical technique that uses high frequency radio waves to map the subsurface. The basic principle of GPR measurements is the transition of electromagnetic pulses of suitable frequency down into the ground through a transmitting antenna, and to detect the reflected energy as a function of time, amplitude and phase from any subsurface targets through a receiver antenna. If the electromagnetic travel velocity of the subsurface is known, time can be converted to depth. Wave reflections are generated from the boundaries of materials of different electromagnetic properties. The large contrast between the electromagnetic properties of rock, ice, water, and some sediments makes GPR a particularly effective method for mapping in frozen environments.A Måla ProEx radar system with a shielded antenna, centre frequency 100 MHz, connected to a handheld Garmin GPS. The antenna was housed in wooden box, slung on a longline, 15 metres long, from the helicopter cargo hook. Two surveys were carried out on the Sørsdal Glacier with the aim of mapping englacial meltwater channels. Outer survey bounds-68.66, 78.302-68.65, 78.532-68.72, 78.544-68.73, 78.313Survey 1 - 21/12/2017 - 11 parallel survey lines 8 km long and 2 cross profiles 3.2 km longSurvey 2 - 22/01/2018 - 12 survey lines 1.3 km long

探地雷达（Ground Penetrating Radar，GPR）是一种主动地球物理探测技术，可借助高频无线电波对地下结构进行成像。探地雷达测量的基本原理为：通过发射天线将合适频率的电磁脉冲发射至地下，再通过接收天线检测来自地下任意目标的、随时间、振幅与相位变化的反射能量。若已知地下介质的电磁波传播速度，即可将传播时间转换为埋藏深度。电磁波反射产生于不同电磁特性介质的分界面处。由于岩石、冰、水与部分沉积物之间的电磁特性差异显著，探地雷达成为冰冻环境下探测成像的高效手段。
本次实验采用搭载中心频率为100 MHz屏蔽天线的Måla ProEx雷达系统，该系统与手持Garmin GPS设备相连。天线被安置于木箱内，并通过一条长15米的吊索悬挂于直升机货运吊钩下方。研究团队在瑟斯达尔冰川（Sørsdal Glacier）开展了两次探测作业，旨在绘制冰内融水通道的分布。
测区范围：68.66, 78.302；68.65, 78.532；68.72, 78.544；68.73, 78.313
第一次探测：2017年12月21日，共布设11条总长8千米的平行测线，以及2条总长3.2千米的横剖面测线
第二次探测：2018年1月22日，共布设12条总长1.3千米的测线