andon their homes. matchbox-sized sensors left in the burrows monitor the Now, these same biologists are checking on the birds occupancy by recording temperature variations inside on the island in the comfort of their offices, browsing and wirelessly send the data to a gateway node on the data from the sensors linked by satellite. And their island. Convenience aside, the more significant benefit colleagues thousands of miles away can share the same of the technology is the minimization of disturbance to Wireless sensor networks CHAPTER 3.7 the very habitat that scientists are trying to help preserve. The experiment on Great Duck Island is a small lens into an expansive future. To grasp what might happen, multiply these 190 sensors by 10 million or 100 million and distribute them globally. When the sensor grid be- comes ubiquitous, an enormous digital retina will stretch over the surface of the planet. This planet-scale system could help us understand and address tomorrow's envi- ronmental challenges, ranging from monitoring global biodiversity to sensing millions of low-level, nonpoint sources of pollution. 3.7.3.2 Tracking chemical plumes: Ad hoc, Just-in-Time deployment for mitigating disasters Image the following scenario. The Valley Authority has just declared a region-wide emergency: A large-scale hazardous chemical gas leak occurred at a chemical processing plant twenty minutes ago. The National Guard has been activated to evacuate nearby towns and to close roads and bridges. To get a real-time situational assessment of the extent and movement of the gas release and help plan the evacuation, the SensorNet SWAT Team is called in. Three unmanned aerial vehicles (UAVs) are immediately launched from an open field 15 miles south of the accident site, each carrying 1000 tiny Figure 3.7-5 Tracking chemical plumes using ad hoc wireless wireless chemical sensing nodes (see Figure 3.7-5). Upon sensors, deployed from air vehicles. flying over the vicinity of the accident site, the sensor nodes are air-dropped. While a