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

英国南极调查局(BAS)近年来开发了一种非常成功的基于通用矢量网络分析仪(VNA)的步进频率相敏雷达系统(PRES)。其目的是获得冰架底部融化速度的直接测量。为了实现这一点，测量了冰架底部相对于冰柱内部反射器的垂直运动。需要两组测量，间隔从几天到一年不等，取决于所需的平均周期。该仪器的现场试验结果超出了所有预期。该系统已被证明是如此敏感，可以测量整个冰柱内部反射器的位移，这意味着可以直接根据PRES确定垂直应变率，而不需要额外的冰川学观测。这项技术的巨大威力在于它对相位的敏感性，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建立PRES系统，并将其用于各种研究，包括在微波频率下运行VNA，以获取地面真实卫星观测的冰盖表面海拔变化。然而，目前的PRES系统使用的是昂贵、笨重、高功耗和高噪声系数的实验室仪器(VNA)，该仪器安装在隔热外壳中，加热到大约22摄氏度的稳定温度。该系统由一台1千瓦的汽油发电机供电。因此，我们提议进行一项研究，以开发和证明一种专门建造、低成本、现场可靠、低能耗的系统的可行性，以及改进性能和(通过卫星)远程数据传输的潜力。然后，可以长期部署这种类型的多个系统，提供全年持续的更新，从而对冰架基础融化速度的演变模式提供一个概括性的看法。建议的系统将基于FMCW架构，使用高度线性的直接数字合成器(DDS)方法，比以前使用的步进频率技术提供更高的性能和灵活性。此外，使用新颖和优雅的相控阵方法提供了诱人的穿过冰的高分辨率3D成像的可能性，这种增强对系统的潜力也将被研究。这项技术目前在TRL2：使用实验室设备在现场证明了使用相敏雷达测量熔体速度的想法。我们寻求资金，以便向TRL4取得进展，以便今后能够对若干地点的冰架融化速度进行全年远程监测。

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.