an autonomous multi-sensor probe for taking measurements under glaciers dr kirk martinez & dr...
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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
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)
PloughmeterPloughmeter
Variations in sediment strength - typical viscous model for sediment behaviourExample from Vestari- Hagafellsjokull, Iceland
SummarySummary
• Current techniques useful, but because they are tethered they do not behave in a ‘natural’ manner
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 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
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
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
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