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Topics: Volcano, Sensor, Wireless sensor network Pages: 28 (8390 words) Published: May 27, 2013
Monitoring Volcanic Eruptions with a Wireless Sensor Network Geoffrey Werner-Allen∗ , Jeff Johnson† , Mario Ruiz‡ , Jonathan Lees‡ , and Matt Welsh∗ University {werner, mdw} † University of New Hampshire ‡ University of North Carolina {mruiz, leesj} ∗ Harvard

Abstract— This paper describes our experiences using a wireless sensor network to monitor volcanic eruptions with low-frequency acoustic sensors. We developed a wireless sensor array and deployed it in July 2004 at Volc´ n a Tungurahua, an active volcano in central Ecuador. The network collected infrasonic (low-frequency acoustic) signals at 102 Hz, transmitting data over a 9 km wireless link to a remote base station. During the deployment, we collected over 54 hours of continuous data which included at least 9 large explosions. Nodes were time-synchronized using a separate GPS receiver, and our data was later correlated with that acquired at a nearby wired sensor array. In addition to continuous sampling, we have developed a distributed event detector that automatically triggers data transmission when a well-correlated signal is received by multiple nodes. We evaluate this approach in terms of reduced energy and bandwidth usage, as well as accuracy of infrasonic signal detection.

I. I NTRODUCTION Wireless sensor networks have the potential to greatly benefit studies of volcanic activity. Volcanologists currently use wired arrays of sensors, such as seismometers and acoustic microphones, to monitor volcanic eruptions. These sensor arrays are used to determine the source mechanism and location of an earthquake or explosion, study the interior structure of the volcano, and differentiate true eruptions from noise or other signals (e.g., mining activity) not of volcanological interest. A typical campaign-type study will involve placement of one or more stations on various sites around a volcano. Each station typically consists of a few (less than five) wired sensors distributed over a relatively small area (less than 100 m2 ), and records data locally to a hard drive or flash card. The data must be manually retrieved from the station, which may be inconveniently located. Power

consumption of these systems is very high, requiring large batteries and solar panels for long deployments. Embedded wireless sensor networks, consisting of small, low-power devices integrating a modest amount of CPU, memory, and wireless communication, could play an important role in volcanic monitoring. Wireless sensor nodes have lower power requirements, are easier to deploy, and can support a larger number of sensors distributed over a wider area than current wired arrays. Using long-distance wireless links, data can be monitored in real time, avoiding the need for manual data collection from remote stations. Such an approach is not without its challenges, however. Volcanic timeseries data are often sampled continuously at rates of 40 Hz or more, far greater than the low frequencies used in environmental monitoring studies [1]. Due to limited radio bandwidth, however, complete signals cannot be captured and transmitted from a large sensor array. For such a network to run for extended periods of time, careful power management techniques, such as triggering and in-network event detection, must be developed. In addition, signals from multiple sensor nodes must be accurately synchronized against a global time base. To demonstrate the use of wireless sensors for volcanic monitoring, we developed a wireless sensor network and deployed it on Volc´ n Tungurahua, an active volcano in a central Ecuador. This network was based on the Mica2 sensor mote platform and consisted of three infrasonic (low-frequency acoustic) microphone nodes transmitting data to an aggregation node, which relayed the data over a 9 km wireless link to a laptop at the volcano observatory. A separate GPS receiver was used to establish a common time base for the infrasonic...
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