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

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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.