Borehole location monitoring using phase-sensitive FMCW radar

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Hot-water drilling is widely accepted to be the most viable method of creating deep boreholes through ice sheets rapidly and cleanly. Up to now, this process is still widely being undertaken 'blind' with little or no information made available to the drillers about the precise trajectory that a borehole is taking as it descends deeper into the ice. The negative consequences of doing this, especially when closely separated boreholes are involved, became evident after the ill-fated first attempt at drilling into Subglacial Lake Ellsworth (SLE). To help rectify this urgent need, the technological development in this project seeks to realise a novel application of phase-sensitive frequency modulated continuous wave (FMCW) radars with an active transponder, to measure from the ice surface the spatial position inside a borehole with centimetre-precision to depths of up to 3-km. It significantly builds upon the successful ApRES radar which has been recently designed and field proven for year-long, high precision measurement of Antarctic ice shelf basal melt rates. The concept of 1D-spatial location using the proposed technique of new phase-sensitive FMCW radars with active transponders is presently at the TRL2 level, in which the basic principles have been observed and reported; and a technology concept has been formulated based on the investigators' recent work at UCL. We now aspire to carry out research to take that concept to TRL4 and validate the technology for 3D-spatial location within a laboratory and outdoor setting. Once realised, the proposed technology could ultimately increase the likelihood of success in future attempts at gaining entry into SLE and other deep (>3000-m) subglacial environments to open up new avenues of scientific exploration. The availability of such an instrument would also address the immediate needs of researchers on both the BEAMISH and CryoEgg NERC-funded projects, who are both seeking an independent method of obtaining spatio-temporal datasets at specific locations at the ice-bed interface and the broader subglacial environment, respectively. The new experimental data provided by the proposed instrument will lead to improved fundamental understanding of the dynamics occurring beneath the polar ice sheets and sustain and boost the status of UK research in these areas to internationally-leading standards.