While it may look like a child's toy, this small, gumball-size device developed at NASA's Jet Propulsion Laboratory, Pasadena, Calif., may someday play a critical role in solar system exploration. A group of these devices, called pods, can be collected together to form a new type of instrument called a sensor web. Photo: NASA

NASA scientists have gone back to the garden, "planting" wireless webs of small sensors in gardens here on Earth in preparation for missions to help monitor biological activity on planets.

Sensor webs like those being tested will help make possible a key NASA goal to establish a virtual presence for exploration throughout the solar system.

NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, and the Huntington Library, Art Collections, and Botanical Gardens, San Marino, CA, have joined forces to study micro-climates, placing webs in the various specialized gardens at the Huntington.

Like satellites and telescopes remotely "measuring" planets across the vast reaches of space, the webs allow large areas to be monitored. Unlike remote operations, sensor webs are placed inside the environment -- thus making them capable of on-site detection not possible from afar. For example, satellite measurements cannot penetrate deep below the ocean surface or detect extremely small quantities of gases coming off a planetary surface. The sensor webs could combine the spatial coverage of a satellite with the precision of an on-site instrument.

"Sensor webs offer us the means to make sensitive measurements over large areas," said Dr. Kevin Delin, leader of the Sensor Webs Project at JPL. "A major thrust of our current effort is to develop a sensor web that can detect, identify and monitor any 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."

A sensor web consists of a number of small pods, each housing transducers that collect data from the environment and communication chips that move the data around the web to primary pods. The information is then transmitted to the Internet or an overhead satellite. "Hopping" the data in short distances from pod to pod makes the overall data transmission more energy efficient. In addition, the "hopped" data is shared by all of the pods, allowing each one to know what is being collected elsewhere on the web.

The pods being tested monitor local temperature, humidity, soil moisture and light levels. Initial observations will take place in a controlled greenhouse environment, then progress to a nursery, and on to overlapping microclimate areas. Pods are housed in small plastic containers about the size of a sandwich box. Other sensor web pods developed by Delin and Shannon Jackson, also of JPL and the lead engineer on the project, look much like a gumball toy, but contain specialized instruments.

This small device, housed in a plastic sandwich-size box, may play a critical role in exploration throughout the solar system, according to scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Called a pod, it is part of a wireless web of interconnected sensing instruments that can monitor large areas for environmental mapping. Photo: NASA

The Huntington Botanical Gardens is a "perfect place," says Delin, to field test the sensor web since there are varied garden environments in the 150-acre grounds that reflect many different micro-climates, from desert to semi-tropical to cool. "We are quite fortunate to be able to work with the staff at the Huntington Gardens to test our system, since they are so experienced in botanical research," Delin said.

This collaboration between institutions is mutually beneficial, according to James Folsom, Director of the Botanical Gardens. "It's always great to work with the scientists from JPL, even more so in this instance. The Huntington's staff sees remarkable potential for the development of these sensors, in both field study and gardens management."

Another advantage to wireless sensor webs is the easy replacement of modules when sensor instruments degrade or batteries fail. New modules, including primary ones, can be added to the web at any time. Multiple webs deployed in a given area will easily mesh with each other. On Earth, webs could be dropped from an airplane, while for other bodies in the solar system, the webs could be released from spacecraft, fired from a lander, or dropped from a small rover. Another possibility is ballistically driving the modules into the steep sides of a canyon for measurements in inaccessible areas.

JPL is a division of the California Institute of Technology, Pasadena.

The Huntington is a private, nonprofit research and cultural center serving both scholars and the general public. The institution is dedicated to the study of history, literature, art, science and culture, as well as to botanical research and education.