Field-ready phase-sensitive radio-echosounder, for ice shelf melt rate measurement

近年来，英国南极调查局（BAS）开发了一种基于通用矢量网络分析仪（VNA）的频率步进相敏雷达系统（pRES）。目的是直接测量冰架底部的融化速率。为了实现这一点的垂直运动的冰架基地进行了测量相对于一个内部反射器内的冰柱。需要两组测量，根据所需的平均周期，间隔从几天到一年不等。该仪器的现场实验结果超出了所有预期。事实证明，该系统非常灵敏，可以测量整个冰柱内部反射体的位移，这意味着可以直接从pRES确定垂直应变率，而无需额外的冰川学观察。该技术的巨大力量在于其对相位的敏感性，允许以毫米精度测量反射器的位移。其他研究小组现在正在使用完全相同的方法构建pRES系统，并将其用于各种研究，包括在微波频率下运行VNA，以地面实况卫星观测冰盖表面高程变化。然而，目前的pRES系统使用昂贵、笨重、高功耗和高噪声系数的实验室仪器（VNA），其容纳在加热到约22摄氏度的稳定温度的绝缘外壳中。该系统由1千瓦汽油发电机供电。因此，我们建议进行一项研究，以开发和证明一个专门建造的，低成本，低功耗和改进性能和远程数据传输（通过卫星）的潜力的现场鲁棒系统的可行性。然后，这种类型的多个系统可以长期部署，提供连续的全年更新，从而可以对冰架基础融化速率的演变模式进行概括性的观察。拟议的系统将基于FMCW架构，使用高度线性的直接数字合成器（DDS）的方法，它提供了更大的性能和灵活性比以前使用的步进频率技术。此外，使用一种新的和优雅的相控阵方法提供了诱人的可能性，通过冰高分辨率3D成像，这种增强系统的潜力也将被调查。该技术目前处于TRL2阶段：使用相敏雷达测量熔融速率的想法已在现场使用实验室设备得到证实。我们寻求资金，以进展到TRL4，以使未来的能力，全年远程监测冰架融化速度在一些地点。

The British Antarctic Survey (BAS) has in recent years developed a highly-successful stepped-frequency phase-sensitive radar system (pRES) based on a general-purpose vector network analyzer (VNA). The aim was to obtain a direct measurement of melt rates at the base of ice shelves. To achieve this the vertical motion of the ice shelf base was measured with respect to an internal reflector within the ice column. Two sets of measurements are required, separated by anything from a few days to a year depending on the desired averaging period. The results from field experiments with this instrument have exceeded all expectations. The system has proved so sensitive that the displacement of internal reflectors throughout the ice column can be measured, which means that the vertical strain rate can be determined directly from pRES without the need for additional glaciological observations. The immense power of the technique lies in its sensitivity to phase allowing the displacements of reflectors to be measured with millimetre accuracy. Other groups are now building pRES systems using precisely the same methods, and using them for various studies, including running the VNA at microwave frequencies to ground-truth satellite-observed surface elevation changes in ice sheet. The present pRES system, however, uses an expensive, bulky, high power consumption and high noise factor laboratory instrument (a VNA), housed in an insulated enclosure heated to a stable temperature of around 22 Celsius. The system is powered by a 1 kW petrol generator. We therefore propose to conduct a study to develop and prove the feasibility of a purpose-built, low-cost, field-robust system with low power consumption and the potential for improved performance and remote data transmission (via satellite). Multiple systems of this type could then be deployed for long periods, providing a continuous year-round update allowing a synoptic view of evolving patterns of ice-shelf basal melt rate. The proposed system would be based on an FMCW architecture, using a highly linear Direct Digital Synthesiser (DDS) approach, which offers greater performance and flexibility than the step-frequency technique used previously. Further, the use of a novel and elegant phased array approach offers the tantalising possibility of through-ice high-resolution 3D imaging, and the potential of this enhancement to the system will also be investigated. The technique is presently at TRL2: the idea of using phase-sensitive radar to measure melt rates has been proved in the field using laboratory equipment. We seek funding to progress to TRL4 in order to allow the future capabiliity of year-round remote monitoring of ice shelf melt rate at a number of locations.