Sensor & communication
technology has advanced rapidly, allowing us to monitor the environment in
greater detail than ever before. Yet, there are challenges. Before designing
and installing any system, it is necessary to understand the physical
environment at each location in detail. The system must be adapted to your
specific site and able to withstand the local conditions. For instance, extreme
weather associated with hurricane season is a concern in our coastal areas and
might be an increasing problem. The goal is to ensure that damage to our sensor
networks during these periods is minimal and that we still collect reliable
data. It is during these extreme events that we might see some of the most
interesting patterns in the data. These and more specific challenges require
advanced planning and critical thinking.
Building complex sensor systems
takes careful planning and is often a collaborative effort between researchers
of different expertise. Programmers
write code to control the actions of the system, technicians install and
maintain sensors and loggers, and data managers handle the scores of incoming
files. All of this has to be planned ahead of time, so that the end product is
something that all stakeholders want to use.
Powering the different systems is
another universal challenge. Using solar energy to keep battery banks charged
can be difficult in remote forested locations.
Dense cloud cover or thick summer tree canopies limit the incoming solar
radiation needed. To compensate, some
systems are overbuilt to ensure it can remain running even during conditions
that are not ideal.
Soil Sensors
The
soil sensor system is fairly complex and built from scratch, requiring a large
amount of work in house before it ever sees the field. When fabricating a
system with so many individual parts, system installation can be a challenge. One
example of this complexity is how the system samples carbon dioxide (CO2)
flux from soil respiration chambers by using two independent control subsystems
relying on many different parts to direct flow. One subsystem is pneumatic
using a compressor to pressurize a device used to open and shut the chambers.
The other uses a pump which pulls samples from the chambers to an analyzer to
quantify soil CO2 flux.
With so many inputs and outputs to
the system, tube and wire control can be demanding. For each CO2
sampling chamber there are two sample tubes which carry the CO2
sample to the analyzer and then back to the chamber, two compression tubes
which operate the actual opening and shutting of the chambers and four sensors
wires used to collect soil data. Keeping things organized and well labeled can
be a slow process to ensure that all the different sets get hooked into the
right part on the system control side.
Working belowground in the granite
state can be difficult when locating areas to install soil sensors and soil chamber
foundations. Probing the ground for
suitable locations is a good start but sometimes is misleading with rocks of
different sizes. To determine if a
location will work before installing a chamber or starting to dig a sensor pit,
first a chamber stencil is used. This
involves drilling out where the chamber support legs will go. If all three legs
can be successfully drilled to the proper depth the next step is to cut along
the inner edge of the chamber to ensure that the chamber will be able to have a
good seal with the soil profile without being offset by rocks.
Once the chamber is in the ground
it is then time to dig a small installation pit on the side of the chamber so
the sensors can be installed. If one
side proves to be too rocky then the other side must be tried. Hopefully we get to the required depth for
sensor installation but if not then a suitable location as close to the chamber
as possible must be utilized.
Aquatic Sensors
Stream flow in headwater drainages
can change dramatically from season to season.
While spring freshets or snowmelt events can be very turbulent, during
the summer streams can slow to just a trickle.
Deploying water quality sensors year-round in these headwater streams takes
careful consideration. To sample stream waters
properly, the sensors should be located in the active flowing channel to get
representative measurements. However, the
channel can be a dangerous place for delicate instruments during storm flow,
which can transport sticks, rocks and other debris that can damage
equipment.
Aquatic sensors package ready for deployment
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Sensors are deployed in a pool at Saddleback Mountain stream,
Deerfield, NH
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An effective deployment strategy in
this type of site involves mounting sensors to a reinforced cage or crate,
which is then secured to the stream bed.
Housings or guards are used to protect the equipment from debris carried
at high flow. This ensures the sensors
are secure during extreme events, while still able to be easily removed from
the stream to be recalibrated when necessary.
Calibrating simply means to adjust a sensor’s measurements based on how
it reads known “standards” for each water quality parameter. This process is important to ensure the data
being collected is reliable, and needs to be done routinely. Weekly stream water samples are also gathered
from sites and run in the laboratory.
Comparing samples analyzed in the lab to the data gathered by the sensors
further ensures data quality.
Water quality sensor deployments during winter months
require additional maintenance during times of extreme cold weather. It is important that researchers are able to examine
seasonal winter patterns in water quality, yet these sensors can be sensitive
to the physical damage associated with icing conditions. When stream pools and runs begin to ice over,
technicians need to be aware of these situations to keep the sensors ice-free,
or ensure that they are safely below the extent of ice cover.
Water quality sensors deployed in winter, safe from ice cover, at Dowst
Cate Town Forest, Deerfield, NH.
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The EPSCoR sensor network can be considered an
outdoor analytical laboratory and as such there are many physical challenges
that arise in a variable climate ecosystem like that of New Hampshire. Careful planning and building is required to
ensure the most accurate and reliable data is obtained. The most difficult places and periods of time
can yield some of the most interesting data to study, but require us to think
critically about how and when to deploy sensors in these environments.
Posted
by Jody Potter, Analytical Instrumentation Scientist III; Brian
Godbois, Senior Laboratory Technician; Lisle Snyder, Laboratory
Technician II, Natural Resources & the Environment, University of New Hampshire