Wireless Monitoring of Rainforest Carbon Flux
Deep in the Costa Rican rainforest, researchers at the La Selva Biological Station are studying the exchange of CO 2 between the atmosphere and dense plant life. This carbon flux study hopes to deepen understanding of the effects of greenhouse gasses on the environment. It has already resulted in the development of a new wireless sensor system that collects a variety of environmental measurements, offers remote configuration capabilities, permits future expansion, and gives researchers around the world access to the measurements over the Internet.
The area under observation lies within a 3,900-acre tropical rainforest that averages more than 150 inches rainfall per year. Rain forests are carbon sinks, meaning they function in a manner that is opposite of a human lung: absorbing CO 2 and releasing oxygen into the environment. Carbon flux in rainforests is unusually complex because of the multilayered, diverse forest structure. Due to the difficulty in making measurements from multiple points on the forest floor and corresponding points in the canopy, a balanced budget for CO 2 fluxes has been historically difficult to measure.
The wireless measurement technology deployed at the site is a networked infomechanical system (NIMS) based on National Instruments LabView software and CompactRio hardware. The NIMS application was developed at the University of California Los Angeles (UCLA) by the Center for Embedded Networked Sensing (CENS). CENS develops embedded network sensing systems for critical scientific and social applications. It is a National Science Foundation (NSF) Science & Technology Center with an interdisciplinary and multi-institutional support structure that involves hundreds of faculty, engineers, graduate student researchers, and undergraduate students from partner institutions throughout California.
Getting the sensor where it’s needed
To increase the accuracy of the measurements being taken and to determine the effects of uneven carbon flux, we developed a mobile, wireless, aerially suspended robotic sensor system capable of measuring the transfer of carbon and other materials between the atmosphere and the Earth.
There are a wide range of measurements necessary to characterize the carbon flux including temperature, CO 2 , humidity, precise three-dimensional wind movement, heat flux, solar radiation, and photosynthetic active radiation (PAR). In the past, acquiring this breadth of measurements required the use of multiple data loggers from different vendors. CENS selected a modular approach using CompactRio to support a wide range of measurements using C Series modules from National Instruments and third-party vendors.
All of the environmental data necessary to conduct the carbon flux study is acquired through a modular approach. The wireless sensor systems are arranged at points on the forest floor and on aerially suspended robotic shuttles. This creates the first environmental monitoring system capable of taking measurements three dimensionally.
Three SensorKit systems ( www.sensorkit.net ) were deployed for the first phase of field trials. These are equipped with a variety of instruments, including tools for conducting basic meteorological measurements, sonic anemometers, infrared sensors, and radiometers.
In the initial test deployment, the wireless mobile sensing platforms traversed cables along three separate transects of the forest understory. During the deployment, the shuttle stopped at 1 m intervals along each transect for 30 seconds to allow sensors to equilibrate and take the required measurements. Each transect pass required 30 minutes and each transect ran for 24 hours.
By implementing the system using National Instruments’ modular hardware and software, we developed a flexible system with the additional communication and configuration advantages available with LabView software. CompactRio was selected as the central measurement collection unit and the Compact FieldPoint network interface with cFP-180x controllers were selected for distributed wireless measurements. A WAP-3701 wireless access point was chosen to transfer data between the distributed sensors, towers, and canopy floor.
Using LabView, we can supply measurements to local researchers in different data formats so they can perform post-analysis. We can configure measurement types, select channels, and even add scaling from a laptop connected to the system. Advanced analysis tools for real-time embedded processing can perform local mass flux analysis and post-processing for remote researchers.
LabView is also equipped with an HMI, so we can see real-time measurements. Prior to the development of this real-time analysis system, researchers typically spent a long time collecting large amounts of data on-site to bring the information back to their respective labs for further analysis.
In conjunction with the system designers at CENS, we plan to expand the system by adding high towers approximately 45 m above the forest floor with canopy walkways and increasing the total number of measurement systems in the upcoming months. Additionally, we plan to deliver remote data access through the Web to researchers and students at other locations. Using a Web browser and the Web capabilities of LabView, researchers everywhere will be able to access and download live and archived data for their own analysis.
Performing additional measurements using a three-dimensional measurement system will provide the data needed to validate our Gap Theory hypothesis that carbon transfer occurs unevenly across the rain forest. Gaps in the forest canopy are sources of carbon loss while the canopy is a source of carbon absorption. With this research, scientists will better understand the carbon absorption impact of rain forests.
|Dr. William Kaiser is in the Department of Electrical Engineering and Dr. Philip Rundel is in the Department of Ecology and Evolutionary Biology, both at UCLA.|