Using sensor Using sensor networks to networks to explore the explore the subglacial subglacial

environmentenvironment

Jane K. HartGeography and EnvironmentUniversity of Southampton

• Glacsweb project

• Learning and tuning

• Results

• Environmental Sensor Network challenges

Design

build

Deploy

learn

Glacsweb aims

• study glacier dynamics

• sensor network research

• produce generic components and expertise useful in other environments

Engineering Challenges

• Probes must be small and reliable• Robust Communications• Adaptive behaviour• Low power for longevity• Live system for experiments and data access

Glacier movement

creep

Subglacial deformation

Sliding/stick-slip motion

Supraglacial data Subglacial data

GLACSWEB:Understand the

role of the subglacial bed in glacier dynamics

BriksdalsbreenBriksdalsbreen

SkalafellsjökullSkalafellsjökull

Site locations• Resting on deformable sediments• GSM phone & local broadband• Good access! • Briksdalsbreen active advance (and

retreat!)

• Skalafellsjökull potential for up to 300m deep analysis.

Briksdalsbreen

Skalafellsjökull

Field site 03 Field site 03 (65m)(65m)

Field sites Field sites 04, 05 & 0604, 05 & 06

(60m),(50m)&(40m)(60m),(50m)&(40m)

2007

2001BriksdalsbreenBriksdalsbreen

Skalafellsjökull, Iceland, 2008-10 (70m)2011 (120m)

System Overview

Base Station

Glacier

SedimentSensor network server

Ref station

Southampton

cloud

geophones

Probes

PC

WiFi

WiFi

Probes

• Polyester case• 433MHz, 173MHz, 151MHz

Radio• Sensors: Temp, Press, Strain,

Resistance, Tilt, Volts• 30 installed in 2003-2008

2004/5

2006

2008

2011

CAD diagrams of probe by Mark Long

ECS Mechanical Workshop

Probe pressure tests in Oceanography

Sensor data buffering

Probes store their data until they manage a connection

Base Station

Ice

Sediment

DD

Ad-hoc network gains

Probes “talk” via best route

Base Station

Ice

Sediment

Base Station

Measure Weather, box tilt,

battery Volts

Radio links gateway and probes

DGPS rover

Ubuntu Linux

ARM CPU

wind & solar power

geophones

Uses 1.4W when on, negligible in Sleep mode

Base station

Base station architectureGPS

(Legacy-H)

GSM(Maestro 20)Gumstix

400MHz ARM

Temp/Hum sensor

Wind power12V Batteries

Wired probe

...

GumsenseMSP430

regulatorSolar power

CF storage

Switching

Gumstix runs Linux

MSP430

sensor interfaces

Reference Station

• Mains power in summer

• Mobile Phone GPRS• Records dGPS data• sends data to farm in

valley 15km away

Live data available on the web

Deployment

Results• 2003/2004 • 14 probe days

• 2004/2005 • 859 probe days

• 2005/2006 • 1255 probe days

• 2008/10• 1205 probe days

• Borehole camera

• Ground Penetrating Radar

• Hot water drilling

• GPS• In situ sampling

• Probes

Ice/Till Interface

Probes in a till–based borehole

Unique results

• High water pressure events

• Quantification of tilt

• Grain behaviour, rheology and water content

• Till temperatures

• Stick-slip events

Water pressureBriksdalsbreen

Autumn

Spring

Winter

Summer

SkalafellsjökullSkalafellsjökull

Water pressure high throughout the year

Series of short term events

-Lake

-Coarse grained till

Briksdalsbreen

-Steep bedrock

-Fine grained till

SkalafellsjökullSkalafellsjökull

Probe tilt

-15.0000

-10.0000

-5.0000

0.0000

5.0000

10.0000

15.0000

20.0000

25.0000

30.0000

8 8 8 8 9 9 9 10 10 10 11 11 11 12 12 12 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7

-60

-40

-20

0

20

40

60

80

100

120

2° / week0.6° / week

3.5° / week

4.2 ° / week y direction

Briksdalsbreen

Rotation

• Two models for clast behaviour in deforming layer – Active rotation (Jeffrey, 1923; Glen et al., 1957; Hart,

1994)

– Stable position (March, 1932; Hooyer & Iverson, 2000)

SkalafellsjökullSkalafellsjökull

-When air temp rise above 2.5o

-wp fall, tilt changes

-This generates high melt-water, allows glacier to ‘slip’

-Afterwards, wp slowly builds up ‘stick’

05

101520

DOY 2005-6

m w

. e.

00.20.40.60.8

kg/k

g

water pressure (m w.e.) water content (kg/kg)

Grain behaviour, rheology and water content High water pressure and water content

-0.15

-0.05

0.05

0.15

DOY 2005-6

mic

rost

rain

s

case strain (microstrains)

Briksdalsbreen

• Grain arrangement as a result of shearing.

• Linear viscous behaviour

after a critical yield stress of 35 kPa

• Till Viscosity (Pa s) 3.6 -7.3 x109

• Till discharge per 1m3 section per year (m3 a-1) 1.3-5.6

High water pressure/weak till

05

101520

DOY 2005-6

m w

. e.

00.20.40.60.8

kg/k

g

water pressure (m w.e.) water content (kg/kg)

-0.15

-0.05

0.05

0.15

DOY 2005-6

mic

rost

rain

s

case strain (microstrains)

Briksdalsbreen

Low water content/strong till

• Stick-slip events directly transmitted via the grain structure through a relatively strong till

0

0.02

0.04

0.06

0.08

0.1

21922

623

324

024

725

426

126

827

528

228

929

630

331

031

732

433

133

834

535

235

9 1 81522293643505764717885929910611

315

012

713

414

114

815

516

216

917

618

319

019

720

424

221

8

Till Temperatures

05

101520

21522

924

325

727

128

529

931

332

734

135

5 4 18 32 46 60 74 88 102

11613

014

415

817

218

620

021

4

DOY 2005-6

m w

. e.

00.20.40.60.8

kg/k

g

water pressure (m w.e.) water content (kg/kg)

-0.15

-0.05

0.05

0.15

215

229

243

257

271

285

299

313

327

341

355 4 18 32 46 60 74 88 10

211

613

014

415

817

218

620

021

4

DOY 2005-6

mic

rost

rain

s

case strain (microstrains)

High water pressures

Low till temperatures

MELTWATER

0

0.02

0.04

0.06

0.08

0.1

21922

623

324

024

725

426

126

827

528

228

929

630

331

031

732

433

133

834

535

235

9 1 81522293643505764717885929910611

315

012

713

414

114

815

516

216

917

618

319

019

720

424

221

8

Till Temperatures

05

101520

21522

924

325

727

128

529

931

332

734

135

5 4 18 32 46 60 74 88 102

11613

014

415

817

218

620

021

4

DOY 2005-6

m w

. e.

00.20.40.60.8

kg/k

g

water pressure (m w.e.) water content (kg/kg)

-0.15

-0.05

0.05

0.15

215

229

243

257

271

285

299

313

327

341

355 4 18 32 46 60 74 88 10

211

613

014

415

817

218

620

021

4

DOY 2005-6

mic

rost

rain

s

case strain (microstrains)

Low and Intermediate water pressure

High till temperatures

‘Flash’ temperatures

• This temperature increases can be accounted for using the ‘flash’ temperature model (Bestmann et al., 2006; Archard, 1958)

Conclusions

• Designed, tested and deployed different probe versions

• Experience in the problems of ESN communications, especially in a glacial environment

• Investigate subglacial processes and stick-slip motion, e.g. water pressure, clast rotation and till temperature.

Challenges for Environmental Sensor Networks

• Power Management • Standardisation• Low cost • Integrating and analysing

large data sets • Development of new

sensors (particularly) biosensors, sensor proxies and envinodes

• Evolution from logging to ESN

• Large Nodes to ‘smart dust’

20032003 20042004

20052005 2006200620062006

20082008

Probe architecture

Base Station Architecture

Power ConsumptionProbes

• 3.6 V Lithium Thionyl Chloride Cells

– 6AH worth of energy

• 4µW in sleep mode

• 370mW in receive mode

• 470mW in transmit mode

• Life aprox. 10 years!!

Base Station

• Powered with lead-acid gel batteries

• 96AH worth of energy

• 120mW in Bitsy’s sleep mode

• 50mW in weather station sleep mode

• Powered up daily for a maximum of 15 min

• Approximate daily consumption 5WH

• Estimated battery life is 230 days

Base 2008

• 36Ah

• 25µW

• maximum of 3 min

• Runs until damaged

Base station battery voltsBase Station Battery Voltage

10

11

12

13

14

16/1

0/05

23/1

0/05

30/1

0/05

06/1

1/05

13/1

1/05

20/1

1/05

27/1

1/05

04/1

2/05

11/1

2/05

18/1

2/05

25/1

2/05

01/0

1/06

08/0

1/06

15/0

1/06

22/0

1/06

29/0

1/06

05/0

2/06

12/0

2/06

19/0

2/06

26/0

2/06

05/0

3/06

12/0

3/06

Date

Vo

lts

Probe Radio link quality based on retry logging

0

10

20

30

40

50

60

70

80

90

100

08 10 10 11 11 11 11 12 12 03 03 03 03 03 04 04 04 05 05 05 05 08 09 09 09 10 10 11 11 11 12 01

Month

Q

2004 2005

Why Briksdalsbreen?

• Part of largest ice sheet in mainland Europe

• Advanced 400 m between 1987 and 1996.

• Resting on deformable lake bed sediments.

• GSM phone & local broadband

• Good access!