This Sensor Web is deployed at the Central Avra Valley Storage and Recovery Project (CAVSARP) facility located west of Tucson, AZ. This particular site was selected because it is ideal for studying spatio-temporal phenomena and for providing a test site for more sophisticated hydrological studies, including that of comparing the data from the Sensor Web to remote measurements taken from orbiting satellites.

The facility provides controlled conditions of soil moisture, from dry (very low moisture) to inundation (soaked). The recharge basins can be flooded with water (up to about 8 feet) and drained at will. This provides a means to use the Sensor Web to track the moving flood front, as well as to follow the penetration of the water into the ground.

The Sensor Web was deployed and activated on November 13, 2003 and consists of 16 pods equipped with sensors for ambient air temperature, relative humidity, and light level. In addition, the Sensor Web pods inside the recharge basin are equipped with a soil temperature sensor (at surface level) and two soil moisture sensors, one buried just below the surface and the second buried at a depth of 0.5 m. These soil sensors are attached to the pods via long leads, which allows the pods to stay above water during flood events. (While the pods themselves are water-tight, pod-to-pod radio communication would not be possible if they were submerged.) The deployment topology was determined by the scientific nature of the study and not limited by technology considerations such as radio range.

Flooding events within the recharge basin can be observed real-time via soil moisture sensor 1 (at the surface) and 2 (buried 0.5 m below) on various pods. The lower the resistance measured from the sensor, the wetter the soil. During controlled flooding events, for example, it is possible to watch the water spread both laterally across the basin from the inlet point in the northwest corner, as well as infiltrate into the ground. Drainage shows the opposite pattern with the south side of the basin drying out first. This can be compared to a rain event, where all the surface soil moisture measurements show increased wetness at approximately the same time.

This Sensor Web ran unattended continuously for 17 months, finally being decommissioned in April 2005. This Sensor Web system not only proved the robustness of the design in a remote, hot environment but also provided insights on the use of Sensor Web technology for Earth Science applications. More details of this research can be found here.

See an aerial map of the pod locations.