It has become common to see spinoffs from the space program finding their way into commercial applications, but at January's Photonics West conference (San Jose, CA) researchers from the Jet Propulsion Laboratory (JPL; Pasadena, CA) described their evolving sensor-web devices as a spinoff of the telecommunications industry and related technologies that is intended to eventually find applications in space.
Currently deployed in prototype form as a microclimate monitoring project in the Huntington Botanical Gardens (Pasadena, CA; see photo), the integrated optoelectromechanical sensing and communication devices are each about the size of a golf ball in one configuration and about the size of a sandwich box in another. They contain an array of solar-powered microchips to sense environmental parameters such as temperature, humidity and air pressure and then transmit that information wirelessly through neighboring sensors in the web to a central data-gathering sensor.
"Sensor webs offer us the means to make sensitive measurements over large areas," said sensor-web project leader Kevin Delin. "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." He characterized the Huntington Botanical Gardens as an ideal setting to field test the sensor web because of the varied garden environments in the 150-acre grounds that reflect a variety of microclimates, from desert to semi-tropical to cool.
As opposed to other distributed sensor networks, sensors in the sensor-web network share information among themselves and modify their behavior on the basis of collected data, according to Delin. Consequently, the sensor web "can perform intelligent autonomous operations in uncertain environments, respond to changing environmental conditions and carry out automated diagnosis and recovery. Sensor webs can have as much of an impact on the uses of sensors as the Internet did on the uses of computers."
Each node in the sensor web contains transducers that collect data from the physical environment and transceivers to communicate data throughout the network. The transducer and transceiver devices consist of commercially available, low-power light, temperature, humidity and other environmental sensors, as well as low power and low bandwidth transceiver technology (such as devices for the 916-MHz ISM band). Light sensors in the Huntington Gardens experiment demonstrated the sensor web concept by communicating individual light level measurements among the nodes to come up with environmental light information in the form of sun position throughout the course of a day. "In its most abstract form, the sensor web can be thought of as an imaging device with each node point a pixel in the phase space represented by the transducer suite," according to Delin.
A major objective of the JPL sensor web project is to support the NASA goal of establishing a virtual presence throughout the solar system.