Thursday, September 26, 2013

Installing sensors in the New Hampshire Environment

                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

Sensors are deployed in a pool at Saddleback Mountain stream, Deerfield, NH

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 sensors deployed in winter, safe from ice cover, at Dowst Cate Town Forest, Deerfield, NH.
 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.
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

No comments:

Post a Comment