FREE RANGE EGGS ETracers and Cryoegg

Wireless sensors for freshwaters

Liz Bagshaw, Jemma Wadham, Steve

Burrow, Ben Lishman, James Bowden,

Lindsay Clare, Dave Chandler

E-T

Motivation • Ice sheets are melting: what’s the consequence of extra

meltwater at the bed for ice sheet stability?

• What are subglacial microbial habitats like?

• How can we collect measurements at many locations

beneath the ice surface?

• In situ measurements in subglacial water channels

• Wireless, untethered sensors

BBC Frozen Planet

Targeted sensor design • Small, low-cost wireless sensor

platforms

• Waterproof and buoyant

• On-board data storage

• Radio-equipped

• Can transmit varying quantities of data to proximal receivers

Two methods

• E-Tracers: along flowpath

• Small, low-cost platforms

• Single parameter

• Data stored on internal memory

• Transmission of summary data

• Potential recovery on emergence from subglacial portal for

data download

• Cryoegg: long term deployments

• Larger platform, multiple sensors

• Larger transmitter

• Data transmitted four times per day

• Sensor recovery unlikely

ETracers: Design

• 50mm sphere

• PIC microchip

• Honeywell pressure sensor

• Radio frequency chip with helical antenna

• Li ½ AA battery (3 month lifetime with 2s chirp, variable)

• Adjustable buoyancy epoxy potting compound

ETracers: Deployment and Detection

• Tracers released into large moulin

• Data recorded on internal EEPROM

• RF transmission allows location of tracer in proglacial stream

• Software radio

• Animal tracking receiver

• Majority of data downloaded on sensor retrieval

• Tracer ID, mean and max transmitted to listener

ETracers: 2010-2011

• Test deployments at Leverett Glacier, SW Greenland in 2009-12

• Moulins 1-15km from the ice sheet margin

• Detection rate varied from 0 to 80% recovery

• Tracers advected much slower than dye released simultaneously,

emerging in 1-35 hr. One tracer took 10 days!

• Tracers frequently became lodged in moulins and/or beneath the ice

Bagshaw et al. 2012 E-tracers: Development of a low cost wireless technique for exploring sub-surface

hydrological systems, Hydrological Processes doi: 10.1002/hyp.9451

ETracers: 2012-2013

• So many tracers delayed in moulins that data retrieval unreliable

• Radio chirp used to transmit data to automated listening station

• Data transmitted through 100m ice and 1km (noise-free) air

• Tracer ID allows assignment of data to each tracer

• One tracer passed through drainage system over 12 days

ETracers: 2013

• Tracers used to measure water level in crevasses in

South Greenland

• Data transmitted 2km to listening station

• Potential for collecting data from

dangerous areas

Cryoegg

Bagshaw et al. In Press for Annals of Glaciology

• Same technology as ETracers

• Larger unit, more sensors

• Also deployed via moulins

• Can transmit more data through

greater distance of ice, water

and sediment

• Data transmitted through 500m

ice to remote receiving stations

• Sensor suite can be changed

– Pressure, temperature, EC

– Biogeochemical sensors

* Subglacial lake applications

Cryoegg: Design

• Higher power radio chip

• 500 mW, 50x ETracers chip

• 120 mm sphere

• Delrin thermoplastic: high strength and rigidity

• Two halves: sensors and power + antenna and

transmitter

• PIC microcontroller, 4 x AA lithium batteries

• O-rings maintain watertight seal

• Sensor recovery not necessary: all data

transmitted

Cryoegg: Sensors

• Radio transceiver • Radiometrix BiM1H

• 500mW output on 151.3MHz

• Temperature • Platinum wire pt1000 sensor

• Embedded in EC bolt

• Electrical conductivity • 2 stainless steel bolts through outside of case

• Potential divider with precision resistor, excited by alternating 500 Hz square wave

• Pressure • Honeywell 0-251 psi gauge pressure

• INTERCHANGEABLE

Cryoegg: Testing

• Binary data transmitted via ASCII encoded chirp

• Communication testing established performance in ice and water

• Acoustic and radio transmission tested

• Good data recovery from:

• Radio: 500m

• Acoustic: 30m

• Expected to improve with better antenna

Cryoegg: Communications

Horizontal distance (m)

0 200 400 600 800

RS

S (

dB

m)

-140

-120

-100

-80

-60

Depth (m)

0 2 4 6 8

RS

S (

dB

m)

-120

-110

-100

-90

-80

-70

Attenuation in ice Attenuation in water

Water attenuates more signal (as expected), but transmission is possible

Prototype tests

• Cryoegg suspended 30m deep in moulin

• Plunge pool at moulin base: 5m deep

• Signal strength tests

• Clear reception despite water

• Data received up to 500m away through ice

Proglacial lake tests

• Egg suspended into 12m of water from ice outcrop

• 24hr data received daily: set transmission times

• Clear reception through 12m water and 50m air

• EC, T and P sensors performed well

Bagshaw et al. In Press for Annals of Glaciology

Cryosphere summary

• Simple, low cost sensors that use off-the-shelf

components

• Sensors can transmit data through up to 500m ice and

15m water

• Data received through up to 2km air

• EC, T and P sensors all operational

• Receivers are flexible:

• Portable, handheld set-up

• Unattended, automated set-up

• ETracers can travel in constricted meltwater flows

Adaptation to temperate systems

• Sensors are powerful method for collecting and transmitting simple data from water to shore

• ‘Free-ranging’ potential enables unique dataset

• ETracers most suitable for UK applications

• Small size (50mm)

• Low cost (parts cost c£50)

• Adjustable buoyancy

• Potential for additional sensors

• Presently pressure equipped

• EC and T to be added shortly

• GPS chip to be incorporated

• Improved receiving system

• Simple receiver

• App for data reporting?

Potential uses

• Free-range:

• Along flowpath data

• Data from set depths

• Distributed floodplain data

• Fixed-point:

• High spatial resolution monitoring

• High temporal resolution

monitoring

• Simple parameters for

characterisation

• Real-time data reporting

Wireless sensors have potential to revolutionise

monitoring of freshwater environments

Only if intelligently designed and sensibly deployed

Need to understand both system and sensor for best results

Complex is not always better

Entirely new datasets, potentially large

How will data be managed?