An autonomous multi sensor probe for taking measurements under glaciers
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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.

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An autonomous multi-sensor probe for taking measurements under glaciers

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An autonomous multi sensor probe for taking measurements under glaciers

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

Advisors

  • Prof. Harvey Rutt

  • Dr Joe Stefanov

  • Workshop: Ken Frampton

  • PIC: Tim Forcer


A subglacial probe an autonomous multi sensor probe for taking measurements under glaciers

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


Introduction

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

Subglacial Deformation

  • Movement in sediment can comprise 90% of glacier motion

  • Requires high pore water pressures


Current research methods

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

Ground Penetrating Radar, example from Breidamerkurjokull


In situ process studies

In situ process studies

  • Sediment strength (ploughmeter)

  • Sediment deformation (tiltmeter)

  • Sediment velocity (dragspools)


Sediment strength

SedimentStrength

Ploughmeter


Ploughmeter

Ploughmeter

Variations in sediment strength - typical viscous model for sediment behaviour

Example from Vestari- Hagafellsjokull, Iceland


Amount of deformation

Amount of deformation

Tilt cells


Tiltmeter

Tiltmeter

-8cm

Variations in tilt

-15cm

Example from Vestari- Hagafellsjokull, Iceland


Amount of deformation sliding

Amount of deformation/sliding

Drag Spools


Summary

Summary

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


Subglacial probe

Subglacial Probe

  • Smart sensor “pebbles” tracked by radio


Site details

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


Properties of ice sediment

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


  • Probe details

    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 strength1

    Sediment Strength

    • Stress gauges in probe

    ICE

    Probe

    SEDIMENT


    Sediment deformation rotation

    Sediment Deformation (rotation)

    • 10 degree accuracy sufficient

    • 2 tilt cells

    ICE

    Probe

    SEDIMENT


    Velocity position

    Velocity(position)

    • 10-50cm accuracy in position

    • Transponder

    ICE

    Probe

    SEDIMENT


    Temperature and pressure

    Temperature and Pressure

    • 1 – 2 C accuracy sufficient

    • Thermistor and Pressure sensor

    ICE

    Probe

    SEDIMENT


    Basic design

    Basic Design

    Base Station

    DGPS

    Ground

    station

    Ice

    Sediment


    Movement in a year

    Movement in a year

    Base Station

    13m

    DGPS

    Ground

    station

    Ice

    10m

    7m

    3m

    Sediment


    Probes

    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

    Radio 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 dBm

      ie within range


    Probe case

    Probe Case

    • Made of strong milled material

    • two halves

    • Use join area for antennae

    • Padded interior


    Base station

    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

    Ground Station

    • DGPS base station to locate base station on glacier


    Power estimate

    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

    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


    Timetable

    Timetable


    Conclusions

    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


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