![](bg3.png)
durations of up to 13 months (Collins et al., 2011).
In addition to the autonomous monitoring operation,
analysis of the data provides a value-added service
by investigating the factors affecting landfill gas
activity, evaluating the contributions of extraction
flow-rate and local weather conditions (barometric
pressure and rainfall). This paper presents the
initialisation of a deployment of multiple sensor
platforms on one site, the first of its type on an Irish
landfill site.
2 PLATFORM DEPLOYMENT
2.1 Deployment Configuration
A wireless sensor network in the form of five
autonomous platforms has been deployed on a single
active landfill site in Ireland. To minimise any
debugging issues and allow for flexibility in locating
the systems, each of the five systems has been
equipped with independent GSM modems for
wireless communications. While this may not satisfy
the classical definition of a wireless sensor network
comprising of a central gateway platform with
peripheral node platforms, the five systems
nevertheless represents the increased spatial
distribution achieved by a sensor network.
There were two configurations of platform
deployed on this site: three units were fitted with
CH
4
and CO
2
infrared gas sensors (Premier Series,
Dynament, UK) for gas concentration monitoring,
two units were fitted with pressure sensors (40PC,
Honeywell, UK) for monitoring extraction pressure.
The two configurations of platforms employed
slightly different data acquisition strategies. The gas
platforms ran a sampling routine every 6 hours, with
data from that sampling routine being transmitted
immediately afterwards. The sample routine
consisted of a two-minute sampling period, where
the sensors took a reading every three seconds as the
pump drew the gas from the landfill’s extraction
network, resulting in 40 readings each for CO
2
and
CH
4
. The two-minute routine enabled a reasonable
volume (~0.6 litres) of gas to be sampled, thus
avoiding any outliers caused by pockets of
concentrated gas. The full dataset of 80 readings was
encoded to fit within the 160 character SMS limit,
whereupon it was transmitted as a text message to
the remote base-station. As the pressure was by
nature more variable, readings were acquired every
30 minutes, stored on flash memory and transmitted
by SMS every 24 hours. Upon reception in the base-
station (based in the lab in DCU), a java program
decoded the text message, parsed the data to a
database via MySQL and uploaded averaged data to
an online portal which could be accessed from a web
browser.
The configuration of the deployment is shown in
Figure 1(ii). The deployment began in December
2011, with two pairs of gas/pressure platforms
deployed in-line with the extraction pipes leading to
each of the two flares on site (locations #1 and #2 in
Figure 1(ii)). The reasoning behind these locations
was that the readings could be validated against the
flares’ SCADA monitoring systems. A third gas
monitoring system was deployed in a newly capped
cell (location #3 in Figure 1(ii)) to monitor the gas
activity as the waste body matured.
2.2 On-site Issue Resolution
As can be expected for outdoor environmental
deployments, there were a number of issues to be
surmounted including power requirements, wireless
communications and sensor readings validity.
Furthermore, there were site-specific issues inherent
to conditions on the landfill site.
A concern with all remote devices is power
provision. For these monitoring platforms, low
power ‘sleep’ algorithms programmed into the
microcontroller circuitry enabled a 10-week
deployment duration using the 12V 5Ah lead-acid
battery. To avoid system downtime, photovoltaic
panels (BP SX-5M) with charge controllers (Solar
Technology STS01208) were fitted to the three gas
monitoring systems. As seen in Figure 2, solar
charging was found to acceptably sustain the battery
level of the system indicating an indefinite
deployment period in terms of power requirements.
Note the 13.5V upper limit in Figure 2 is not
representative of the actual battery voltage but
instead is the maxed-out voltage potential across the
solar panel during daylight hours. A truer reading of
the battery level is the night-time values - the
minima in Figure 2 (ii). Solar charging was not
necessary for the pressure monitoring systems which
had an estimated battery life of 12 months due to the
lack of the pump and power hungry IR sensors.
Figure 2: Power levels during operation (i) battery
depletion rate, (ii) battery solar recharging.
(i)
(ii)
SENSORNETS2013-2ndInternationalConferenceonSensorNetworks
224