Life Under your Feet: A W ireless Soil Ecology Sensor Netw ork R. - - PowerPoint PPT Presentation

EmNets 2006 Life Under your Feet 1

Life Under your Feet:

A W ireless Soil Ecology Sensor Netw ork

• R. Musaloiu-E†., A. Terzis† , K. Szlavecz‡ , A. Szalay*,
• J. Cogan*, J. Gray◊

† Computer Science Department, JHU ‡ Earth and Planetary Sciences Department, JHU * Physics Department, JHU ◊Microsoft Research

I n the Beginning…

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• The Cast
• An ecologist: Katalin Szlavecz
• An undergrad student working

in a summer project: Joshua Cogan

• The Stage
• The urban forest near the JHU

campus

• Off-the-self soil moisture and

temperature sensors

• A few Mica2 motes
• The Goal
• Test whether WSNs can be

used to collect soil monitoring data at spatial and temporal scales larger than that of data loggers

First Step

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• The sensors were

thoroughly tested in the lab

• 2 out of 6 sensors

misbehaved

• Relatively precise (+/-

0.5°C)

• … but offset of 1.5°C from

a NIST approved thermocouple.

• Next step: teach the motes

to play their part.

Second Step

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• More actors:
• CS faculty (Andreas Terzis)
• CS grad student (Razvan Musaloiu-E.)
• DB experts: Alex Szalay and Jim Gray
• More setup:
• MicaZ motes
• MSSQL
• Skyserver DB software
• The goal
• Build an end-to-end data collection

system

System requirem ents

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• Measurement fidelity
• All the raw measurements should be collected and

persistently stored

• Measurement accuracy and precision
• Temperature data error < 0.5 C, volumetric moisture data

error < 1%.

• Fusion with external sources
• Comparing measurements with external data sources is

crucial

• Additional Requirements
• Sampling Frequency: minutes
• Experiment Duration: years
• Deployment Size: networks should be deployed in ways

that capture the heterogeneity of land use

System Architecture

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Sensor Node Hardw are

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• Sensors:
• Watermark soil moisture
• Irrometer soil thermistor
• Onboard Temperature and Light
• MicaZ motes
• Waterproof cases, cables, connectors, ...

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Mote Softw are

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Mote Base 1s 2min (b) (a)

...

Mote Bulk Phase Sending Base

... Receiving data message status message data request

Send−and−Wait Phase

• Sensors are sampled every minute
• Raw measurements are stored in flash
• Storage overrun in > 20 days
• Data retrieved using NACK-based sliding window protocol
• Each mote sends every 2 min a status messages to base-

station: (#meas, bat voltage)

• Web-accessible real-time monitoring

Database Design

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• DB Design derived from

experiment and WSN setup

• Self-documenting

framework

• Raw data follow a multi-

stage validation process

• Stored data available

through Web pages and Web Services

• Datacube for analysis
• 7M datapoints collected

Calibration w orkflow

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Temperature Sensor Calibration Temperature Sensor Calibration Soil Temperature Soil Temperature Water Content

Volumetric

Water Content

Volumetric

Soil Water Potential-> Volumetric Conversion Soil Water Potential-> Volumetric Conversion Voltage Voltage Voltage Voltage Voltage Voltage Moisture sensor

A/D units

Moisture sensor

A/D units

Reference voltage

A/D units

Reference voltage

A/D units

Temperature sensor

A/D units

Temperature sensor

A/D units

CPU clock CPU clock Air Temperature

A/D units

Air Temperature

A/D units

Light Intensity

A/D units

Light Intensity

A/D units

Temperature Conversion Temperature Conversion Air Temperature

Celsius

Air Temperature

Celsius

UTC DateTime UTC DateTime Resistance Resistance Resistance Resistance Mote Resistor Calibration Mote Resistor Calibration Moisture Sensor Calibration Moisture Sensor Calibration Water Deficit

Soil Matrix Potential

Water Deficit

Soil Matrix Potential

Calibrations in the Lab Calibrations in the Lab

Deploym ent Site

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• 10 motes deployed on a slanted grid, ~2m apart
• 147 days of deployment
• Basestation within direct radio range
• Some links had unexpectedly poor quality
• Had to collect some of the data using laptop

2m 8m 2m

Ecology Results ( Tem perature)

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Ecology Results ( Soil Moisture)

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Energy consum ption

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• Motes go to sleep when

not collecting data/sending reports

• Easy to calculate

average current draw

• Powered by AA alkaline

batteries

• Linear discharge curve
• Possible to predict node

lifetime

Data Transm ission Perform ance

EmNets 2006 Life Under your Feet 17 Good Link Lossy Link

Problem s w e encountered

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• Waterproofing the boxes
• Moisture sensor behavior in

the wild

• Power consumption
• Data provenance
• Reprogramming

Conclusions

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• Sensor Networks are still expensive in time, money and

know-how

• Need for data analysis tools
• Need for increased confidence in collected

measurements

• End-to-End system that transform s raw

m easurem ents to scientifically significant data

Questions?

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• For more information

http://www.lifeunderyourfeet.org/