Volume 9, Number 3 • May/June 2001

Sensor Webs Are Virtual Explorers

Wireless webs of tiny sensor pods created to aid in monitoring biological activity on Earth may eventually be used to help explore other planets.

Scientists at NASA’s Jet Propulsion Laboratory (JPL) have created the webs, which will be first used to provide additional information on Earth-based issues like the carbon cycle. Later, the webs could be used to search for evidence of life on Mars or explore the moons of Jupiter.

A sensor web is a system of wireless, intra-communicating, spatially distributed sensor pods that can be deployed to monitor and explore new environments. According to Kevin Delin, one of the scientists who developed the sensor web concept, each pod collects local information through its sensors and communicates that information wirelessly to neighboring pods. In this way, the information is distributed throughout the entire web. The information is then transmitted to a remote source, such as a computer or mobile phone. Eventually, if the web were used in space exploration, it would transmit the information to a satellite or space probe.

“A sensor web is capable of automated reasoning,” Delin said, “because it can perform autonomous operations in uncertain environments, respond to changing environmental conditions and carry out automated diagnosis and recovery. Sensor webs could have as much an impact on the use of sensors as the Internet did on the use of computers.

“Each little pod is like a cell of your body,” Delin said. “The sensor webs are different from distributed sensors in that distributed sensor networks gather data and communicate it to a central point. The sensor web pods gather and, more importantly, share information with other pods. The sensor webs modify their behavior on the basis of the collected data.”

Sensor Web 3 is currently being developed for the Huntington Botanical Gardens in San Marino, California, also the test site for Sensor Web 2. A botanical greenhouse was chosen for the deployment site of the web for several reasons, according to Delin. “Many basic applications, particularly those in astrobiology and Earth science, would require a suite of sensors similar to those needed in this environment,” he said. “Second, a greenhouse would provide somewhat harsh conditions, such as high temperatures, high humidity and dirt, that would make a field test meaningful.”

The information collected by Sensor Web 3 includes measurements of air temperature, soil temperature, relative humidity, soil moisture and the light level. “Sensor webs offer us the means to make sensitive measurements over large areas,” Delin added. “A major thrust of our current effort is to develop a sensor web that can detect, identify and monitor biological activity. For example, trace biosignature gases are very important if you are a biogeochemist trying to understand the carbon cycle on Earth or searching for microorganisms living beneath the surface of a planet.”

The sensors themselves can determine the cost of deploying a sensor web, since the sensors and hardware being used in the sensor pods are commercially available, off-the-shelf products that have been developed for computers and mobile telephones.

The JPL Sensor Webs Project is also beginning to develop a partnership with NASA Kennedy Space Center to look at marine biology in the area.

According to Delin, the sensor web also has applications for saving human life in space and on Earth. The sensor web can show the direction of gas flow and available exit routes by providing vectored direction in both time and space. “The webs can be used in space to not only detect a loss of pressure in a spacecraft, but to pinpoint the leak so the correct section of the craft can be closed off.

“And imagine if you had sensor webs in your house,” Delin said, “so that instead of just having a smoke alarm go off, you actually had an idea which direction the fire is coming from so you knew how to escape it.”

For more information, visit http://sensorwebs.jpl.nasa.gov, or contact Kevin Delin at Jet Propulsion Laboratory, 818/354-9647, kevin.delin@jpl.nasa.gov. Please mention you read about it in Innovation.