irborne, the nodes self- demonstration in the Mojave Desert of Southern organize into an ad hoc network and relay the sensing California. Each sensor node is equipped with a micro- result back to the UAVs nearby: Where is the plume? processor, an RF modem, and a magnetometer. Including How big is it? What is the shape? How fast is it moving? the battery, the sensor node weighs about an ounce. The While the full realization of this scenario may take UAV air-dropped six wireless sensors along a road several years, pieces of the sensor network technology (Figure 3.7-6). Once on the ground, the sensors imme- have already been demonstrated. For example, in March diately self-organized into a network, initiated detection 2001, Kris Pister and his Berkeley team deployed wire- when a vehicle passed by, and relayed the tracking results less sensors using a UAV for a vehicle tracking field back to the UAV. Figure 3.7-6 Left: Berkeley wireless sensor mote. Right: Air-drop of six sensor nodes from a UAV. (Picture courtesy of Kris Pister and Jason Hill). CHAPTER 3.7 Wireless sensor networks 3.7.3.3 Smart transportation: Networked When these sensors are networked together to share Sensors making roads safer and less real-time information, we can begin to create a dynamic congested infrastructure for smart roads that can be optimized to make roads safer, reduce congestion, or help people find Plenty of sensors are already in use for traffic monitoring the nearest available parking space in an unfamiliar city. purposes (see Figure 3.7-7). Sensors embedded in For example, cars and trucks equipped with wireless sensors can warn each other of imminent collision or roadbeds or alongside highways measure traffic flow. Cameras at street intersections look for traffic violations. other road hazards ahead. They can dynamically optimize Sensors in vehicles monitor speed and other conditions. routes to avoid traffic hot spots. They can continuously monitor their own conditions and transmit emission data But today these sensors do not talk