An autonomous multi-An autonomous multi-sensor probe for taking sensor probe for taking measurements under measurements under

glaciersglaciers

Dr Kirk Martinez & Dr Jane K. HartDr Kirk Martinez & Dr Jane K. HartElectronics and Computer Science & Dept. of Electronics and Computer Science & Dept. of

GeographyGeography

AdvisorsAdvisors

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

A Subglacial ProbeA Subglacial ProbeAn 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

IntroductionIntroduction

• 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 DeformationSubglacial Deformation

• Movement in sediment can comprise 90% of glacier motion

• Requires high pore water pressures

Current research Current research methodsmethods

• Geophysical techniques (seismic and radar) are mostly static and of low resolution

• In situ process studies

Ground Penetrating RadarGround Penetrating Radar

Ground Penetrating Radar, Ground Penetrating Radar, example from Breidamerkurjokullexample from Breidamerkurjokull

In situIn situ process studies process studies

• Sediment strength (ploughmeter)

• Sediment deformation (tiltmeter)

• Sediment velocity (dragspools)

SedimentSedimentStrengthStrength

Ploughmeter

PloughmeterPloughmeter

Variations in sediment strength - typical viscous model for sediment behaviourExample from Vestari- Hagafellsjokull, Iceland

Amount of Amount of deformationdeformation

Tilt cellsTilt cells

TiltmeterTiltmeter

Variations in tilt

-8cm

-15cm

Example from Vestari- Hagafellsjokull, Iceland

Amount of Amount of deformatiodeformation/slidingn/sliding

Drag Drag SpoolsSpools

SummarySummary

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

Subglacial ProbeSubglacial Probe

• Smart sensor “pebbles” tracked by radio

Site detailsSite details• Briksdalsbreen in Norway• Advanced 400m since 1988 over silty

clay (lake bed)• Average July surface velocity 1996-2000

was 0.33 m/day - basal velocity normally 70% of surface so predicted velocity 0.23 m/day

• Expected deforming bed thickness: 0.2 - 0. 3m

• Expected ice thickness at drill site: 100m

Properties of Properties of ice/sedimentice/sediment

• dielectric constant of ice: ≈ 3.17 ≈ 0.003

• frozen sediments ≈ 3.8 • dry sediments ≈ 4.4• DC conductivity ≈ 10-5 to 10-6 S m-

1

Probe DetailsProbe 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 StrengthSediment Strength

• Stress gauges in probeICE

SEDIMENT

Probe

Sediment Deformation Sediment Deformation (rotation)(rotation)

• 10 degree accuracy sufficient

• 2 tilt cells

ICE

SEDIMENT

Probe

VelocityVelocity(position)(position)

• 10-50cm accuracy in position

• Transponder

ICE

SEDIMENT

Probe

Temperature and Temperature and PressurePressure

• 1 – 2 C accuracy sufficient

• Thermistor and Pressure sensor

ICE

SEDIMENT

Probe

Basic DesignBasic Design

Base Station

DGPSGround station

Ice

Sediment

Movement in a yearMovement in a year

Base Station

DGPSGround stationIce

Sediment

13m

10m

7m

3m

ProbesProbes

• 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 calculationsRadio calculations

• Velocity in ice ≈ 0.16 m/ns• 1.8GHz wavelength = 0.167 m = 4 Im(√) / = 0.063 m-1

• Attenuation = e - L

For L = 100m Attenuation = 27 dBmie within range

Probe CaseProbe Case

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

Base StationBase 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 StationGround Station

• DGPS base station to locate base station on glacier

Power estimatePower 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

TestingTesting

• Mechanical testing of case• Telemetry testing• Sensor testing/calibration• Accelerated power drain testing at

-5oC• Traditional instruments will also be

inserted in glacier for comparison

TimetableTimetable Project Activities PDRA

employed Oct-J une 2002/3 Construction of the systems J uly-Sept 2003 Insertion of the probes

beneath the glacier

Oct-J une 2003/4 Data collection and interpretation

- Summer 2004 Second field season - Sept-Dec 2004 Continued data collection and

analysis and publication of results

-

ConclusionsConclusions

• 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