An autonomous multisensor probe for taking measurements under glaciers

1
An autonomous multi-sensor probe for taking
measurements under glaciers

• Dr Kirk Martinez Dr Jane K. Hart
• Electronics and Computer Science Dept. of
  Geography

2
Advisors

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

3
A 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

4
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

5
Subglacial Deformation

• Movement in sediment can comprise 90 of glacier
  motion
• Requires high pore water pressures

6
Current research methods

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

7
Ground Penetrating Radar
Ground Penetrating Radar, example from
Breidamerkurjokull
8
In situ process studies

• Sediment strength (ploughmeter)
• Sediment deformation (tiltmeter)
• Sediment velocity (dragspools)

9
SedimentStrength

• Ploughmeter

10
Ploughmeter
Variations in sediment strength - typical viscous
model for sediment behaviour
Example from Vestari- Hagafellsjokull, Iceland
11
Amount of deformation

• Tilt cells

12
Tiltmeter
-8cm
Variations in tilt
-15cm
Example from Vestari- Hagafellsjokull, Iceland
13
Amount of deformation/sliding

• Drag Spools

14
Summary

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

15
Subglacial Probe

• Smart sensor pebbles tracked by radio

16
Site 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

17
Properties of ice/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

18
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

19
Sediment Strength

• Stress gauges in probe

ICE
Probe
SEDIMENT
20
Sediment Deformation (rotation)

• 10 degree accuracy sufficient
• 2 tilt cells

ICE
Probe
SEDIMENT
21
Velocity(position)

• 10-50cm accuracy in position
• Transponder

ICE
Probe
SEDIMENT
22
Temperature and Pressure

• 1 2 C accuracy sufficient
• Thermistor and Pressure sensor

ICE
Probe
SEDIMENT
23
Basic Design
Base Station
DGPS Ground station
Ice
Sediment
24
Movement in a year
Base Station
13m
DGPS Ground station
Ice
10m
7m
3m
Sediment
25
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

26
Radio calculations

• Velocity in ice 0.16 m/ns
• 1.8GHz wavelength 0.167 m
• ? 4 ? Im(v?) / ? 0.063 m-1
• Attenuation e - ? L
• For L 100m Attenuation 27 dBm
• ie within range

27
Probe Case

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

28
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

29
Ground Station

• DGPS base station to locate base station on
  glacier

30
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

31
Testing

• 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

32
Timetable
33
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