An autonomous multi-sensor probe for taking measurements under glaciers Dr Kirk Martinez & Dr Jane K. Hart Electronics and Computer Science & Dept. of Geography

Advisors Prof. Harvey Rutt Dr Joe Stefanov Workshop: Ken Frampton PIC: Tim Forcer

A Subglacial Probe A Subglacial Probe An autonomous multi-sensor probe for taking measurements under glaciers Introduction Current Research Methods Subglacial Probe –Site details –Radar details of ice/sediment –Probe details Revised Timetable and Conclusion

Introduction Current day ‘Global Warming’ represents one of major changes to our social and environmental well being One key element of climate change is the response of glaciers - sea level change, and changes to the thermohaline circulation in the North Atlantic Vital to understand behaviour of the subglacial bed

Subglacial Deformation Movement in sediment can comprise 90% of glacier motion Requires high pore water pressures

Current research methods Geophysical techniques (seismic and radar) are mostly static and of low resolution In situ process studies

Ground Penetrating Radar Ground Penetrating Radar, example from Breidamerkurjokull

In situ process studies Sediment strength (ploughmeter) Sediment deformation (tiltmeter) Sediment velocity (dragspools)

Sediment Strength Ploughmeter

Ploughmeter Variations in sediment strength - typical viscous model for sediment behaviour Example from Vestari- Hagafellsjokull, Iceland

Amount of deformation Tilt cells

Tiltmeter Variations in tilt -8cm -15cm Example from Vestari- Hagafellsjokull, Iceland

Amount of deformation/ sliding Drag Spools

Summary Current techniques useful, but because they are tethered they do not behave in a ‘natural’ manner

Subglacial Probe Smart sensor “pebbles” tracked by radio

Site details Briksdalsbreen in Norway Advanced 400m since 1988 over silty clay (lake bed) Average July surface velocity was 0.33 m/day - basal velocity normally 70% of surface so predicted velocity 0.23 m/day Expected deforming bed thickness: m Expected ice thickness at drill site: 100m

Properties of ice/sediment dielectric constant of ice:  ≈ 3.17  ≈ frozen sediments  ≈ 3.8 dry sediments  ≈ 4.4 DC conductivity ≈ to S m -1

Probe Details Sediment strength Sediment deformation Sediment velocity Sediment temperature Holes will be drilled by hot water drill Probes will be inserted at 5 sites

Sediment Strength Stress gauges in probe ICE SEDIMENT Probe

Sediment Deformation (rotation) 10 degree accuracy sufficient 2 tilt cells ICE SEDIMENT Probe

Velocity (position) 10-50cm accuracy in position Transponder ICE SEDIMENT Probe

Temperature and Pressure 1 – 2 C accuracy sufficient Thermisto r and Pressure sensor ICE SEDIMENT Probe

Basic Design Base Station DGPS Ground station Ice Sediment

Movement in a year Base Station DGPS Ground station Ice Sediment 13m 10m 7m 3m

Probes Hard oval case probably potting-filled PIC microprocessor & RAM Data Transmitter & radar transponder A/D and amplifiers Powerful batteries Sensors: tilt, temp. pressure, … May measure hourly, transmit and sleep

Radio calculations Velocity in ice ≈ 0.16 m/ns 1.8GHz wavelength = m  = 4  Im(√  ) /  = m -1 Attenuation = e -  L For L = 100m Attenuation = 27 dBm ie within range

Probe Case Made of strong milled material two halves Use join area for antennae Padded interior

Base Station Computer with larger storage Large power supply (lead-acid gell plus Solar top-up) DGPS for position relative to ground station Receiver for Probe data GSM/Satellite phone connection home Position radar antennas to track probes

Ground Station DGPS base station to locate base station on glacier

Power estimate 400mA for 2s every hour is 2AH/year Lithium AA batteries reach 2-3 AH Estimate 6 batteries for 7V approx. Can reduce on/off ratio if necessary

Testing Mechanical testing of case Telemetry testing Sensor testing/calibration Accelerated power drain testing at -5 o C Traditional instruments will also be inserted in glacier for comparison

Timetable

Conclusions Probe allows: –less invasive monitoring of the subglacial –more natural mimicking of clast behaviour Technical solution is feasible This will be the first instrument of its kind for earth observations