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Remote Sensing in Extreme EnvironmentsTaking measurements in hazardous, remote and ecologically important areas is becoming easier due to advances in wireless and new sensor technologies.by Tim Studt
Researchers are able to collect diverse environmental data using wireless systems connected between towers in a Costa Rican forest canopy.
Photo: NI/UCLA | Lab work alone is not always conducive to the data collection requirements of researchers. Field measurements for environmental, hazardous and distant applications often need to be collected in places where researchers cannot go. This article provides examples of the technologies for three of these remote measurement applications: carbon flux in the jungles of Costa Rica, thermal gradients and mineral deposits on Mars, and ozone precursors in industrial processes.
Remote sensing in these environments is transitioning from wired to wireless-based systems that provide real-time data, or as close to real-time as possible. In some cases, some type of measurement collection system has been in place for several years, with upgrades to the most current sensor and data acquisition systems being implemented.
Rain forest ecology
Researchers led by Philip Rundel at the Univ. of California, Los Angeles, are developing a network of wireless environmental sensors at the La Selva Biological Station in north-central Costa Rica to generate data for estimating the exchange of CO2 (carbon flux) in the tropical rain forest. The 3,900-acre La Selva site is run by the Organization for Tropical Studies (OTS), a non-profit consortium of 63 universities and research institutions from the U.S., Latin America and Australia.
The La Selva site has been in operation for about 40 years and is one of three OTS facilities—the others are in Palo Verde National Park in the northwestern Pacific lowlands and in Costa Rica’s southern Pacific slopes (Las Cruces Biological Station).
While wired networks for some type of environmental monitoring studies have been deployed globally for decades, wireless systems have only recently been developed to meet the specific research needs for remote sites.
“Our system measures the microclimate with sensors for temperature, relative humidity, leaf wetness, wind speed and direction, photosynthetic active radiation, soil sensors and more,” says Rundel. Their wireless measurement technology is a networked infomechanical system (NIMS) based on National Instruments’ (NI) LabVIEW software and CompactRIO hardware. The NIMS application was developed at William Kaiser’s Center for Embedded Networked Sensing (CENS) at UCLA.
To create a flexible, reliable and accurate system, the sensors used by Rundel and Kaiser are part of a mobile, wireless, aerially suspended robotic system at La Selva. Three of these “sensorkits” have been deployed at the site for the first phase of field trials. They run on cables between radio towers within the rain forest for horizontal measurements and have lowering and raising mechanisms for vertical measurements. The 25- to 46-m towers that these sensorkits run on are elevated above most of the 30-m rain forest canopy.
ASU's Phil Christensen uses the THEMIS telescope for imaging the Martian landscape (background).
Photo: Arizona State Univ. | NI’s CompactRIO was selected as the central measurement unit, and the NI Compact FieldPoint network interface with cFP-180x controllers was selected for the distributed wireless measurements. The researchers used NI’s Access Point (WAP-3701) to transfer data between the distributed sensors, the towers and the canopy floor.
While this sensor network is wireless, the overall La Selva site is still powered by a conventional electrical grid, which has encountered some typical physical and political Central American issues in being completed. For example, the La Selva rain forest receives about 13 feet of annual rainfall and has indigenous animals, insects and plant life that rapidly infest everything.
Other issues include funding for the overall study. The National Science Foundation provided an initial grant for the hardware, but alternative funding is needed for the salaries of those maintaining the system.
Creating these wireless monitoring systems, however, is just the beginning to being able to understand the carbon flux in a tropical rain forest, according to Rundel. “Existing models for measuring carbon flux don’t balance well,” he says. Models and algorithms for the absorption of CO2 and the release of oxygen into the atmosphere “don’t account for leakages, such as that in treeless gaps in the rain forest.”
These ecological monitoring studies are especially important to gauge the impact of greenhouse gases on the environment and the resulting response in the rainforest. Tropical rain forests absorb more CO2 than any other terrestrial ecosystem and affect the climate both locally and globally. The multilayered, diverse forest structure, however, is particularly complex.
Even well established ecological measurement sites within the U.S. provide a variety of mixed data that’s very open to interpretation, according to Rundel. He estimates that it will take another 10 years of testing, model development and data analysis until researchers are able to provide reliable data on the carbon flux within a tropical forest environment.
 Low-Power Wireless
At its recent user meeting, National Instruments introduced a new wireless sensor network (WSN) that provides a complete remote monitoring solution that consists of NI’s LabVIEW software and new reliable, low-power wireless measurement nodes. The nodes operate on four AA batteries and deliver up to 3 years of battery life at one sample/minute. The WSN-3202 voltage node offers four 16-bit analog inputs and four digital I/O lines and can source up to 20 mA at 12 V for powering external sensors. The platform offers reliable connectivity from a gateway to end nodes at a distance up to 300-m line-of-sight. Using mesh networking, routers extend the total distance from a gateway to an end node. |
Extraterrestrial monitors
Measuring and monitoring the environment of the planet Mars has been underway for the past decade with several NASA spacecraft. The Mars Odyssey spacecraft was launched from Kennedy Space Center on April 7, 2001 and arrived at Mars on October 24, 2001. After several months of maneuvering into a circular mapping orbit, it began mapping operations in February 2002. Odyssey’s instruments include a samma ray spectrometer, (GRS), thermal emission imaging system (THEMIS), and Mars radiation environment experiment (MARIE). The THEMIS spectrometer was developed by researchers at the Mars Space Flight Facility (MSFF) at Arizona State Univ., Tempe.
ASU also developed two miniature thermal emission spectrometers (Mini-TES) for the Mars Exploration Rovers, Spirit and Opportunity. The Rovers were launched in June and July 2003 and landed on Mars in January 2004. Scientists initially planned for only six months of service from the Rovers, but they’re still functioning more than five and a half years later. After more than seven years in orbit, the Odyssey’s THEMIS infrared (IR) spectrometer also continues to send back information; however, a large solar event bombarded Odyssey in October 2003, damaging the MARIE computer board and making it inoperable.
The Rover spectrometer data is used to determine where next to drive the vehicles to collect more geological data.
The most significant effect on these spectrometers has been that of dust on the Rover’s optical systems, according to Phil Christensen, Director of ASU’s MSFF. The optical system consists of a periscope/telescope and mirrors at the center of the vehicle with a flap-like cover that opens to make measurements.
“Initially, we had the cover open 4 to 5 hour/day, but the dust has accumulated so much that we now only open it about 0.5 hour/day to extend its life,” says Christensen.
When initially designed more than 10 years ago, no mechanism was included in to clean the optical system—they were considered too complex with too many things that could fail. “One Rovers’ spectrometer system has accumulated so much dust that its short wavelength measurements (5 to 15 microns) are no longer available; the longer wavelengths (15 to 25 microns), however, are still available,” says Christensen.
Dust is not as much a problem for the Rover’s horizontal solar panels because the Martian winds have a tendency to blow off any accumulation there.
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PerkinElmer’s On-Line Ozone Precursor Analyzer includes a Clarus GC and TurboMatrix Thermal Desorber. | Precursor analyzers
The Clean Air Act of 1970 gave the Environmental Protection Agency (EPA) responsibility for maintaining clean air for health and welfare. The resulting rules created by the EPA—similar rules were made for the European Community—resulted in the development of specialized instruments for taking measurements 24/7 in remote locations. One such instrument is PerkinElmer’s On-line Ozone Precursor Analyzer, which includes a Clarus gas chromatograph and TurboMatrix Thermal Desorber.
“These systems run unattended for an indefinite period of time, depending upon the specific application and the type of carrier gas the customer wants to use for the system,” says Massimo Santoro, GC product manager for PerkinElmer. “You can’t apply the normal rules for these applications because the type and amount of carrier gas needed might limit your flexibility. You might need to have someone come out and deliver new gas tanks once every three weeks or so.”
The analyzer has been simplified with everything performed through the instrument’s built-in computer. “The GC application is handled in a very clever manner with the built-in thermal desorber,” says Santoro. The measurement cycle is generally built around the EPA’s requirement for hourly measurements for most processes. Collection of air samples is performed with a vacuum pump for about 40 minutes to a cold trap and then heated, which releases the volatile organic compounds (VOCs) collected to a GC for analysis, all within the 1-hour timeframe. Software controls all of the thermal desorption and GC operations.
Little has changed since the 1970 Clean Air Act in terms of new regulations. Upgrades in the instrumentation continue to be made, so newer systems are more efficient in their measurements. Space is also not a critical requirement in most of these applications, so downsizing the device also is not important. “If the regulations were to change, we might be required to change,” says Santoro.
For more info, contact PerkinElmer’s Giulia Orsanigo at Giulia.Orsanigo@perkinelmer.com; ASU’s Phil Christensen at phil.christensen@asu.edu; UCLA’s Phil Rundel at rundel@biology.ucla.edu; and National Instruments’ Robert Jackson at Robert.jackson@ni.com
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