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Sensors Probe for Data in Ice and Mud
University of Southampton researchers have deployed wireless sensor systems to gather information about glacier movement, as well as forecast mudslides.
Nov 02, 2010—For the past two years, researchers at the University of Southampton have observed conditions within a glacier in the mountainous reaches of Iceland from their office in the United Kingdom, thanks to a prototype wireless sensor system that the group is testing. During that period of time, however, the system has suffered from data interruptions and shutdowns, caused by power failures or harsh winter weather. Next year, the research team aims to further improve the system with additional battery power for the sensor nodes, as well as a Wi-Fi system for more reliable, faster connectivity to software running on a back-end server.
The wireless sensors system (dubbed Glacsweb) is intended to help the scientists track the behavior of glaciers as they melt and move over time, by measuring the ice sheets' motion, angle and temperature, and then transmitting that information to software that can be accessed via the Internet. The ultimate goal is to learn more about glacial "stick-slip" motion, in which ice flows in phases—sticking for a time, and then moving quickly through a slip phase. The technology, custom-built by university researchers and installed two years ago on Iceland's Skalafellsjökull Glacier, included eight sensors, only three of which are currently still transmitting.
In the coming year, the researchers plan to use new more sensitive sensors to detect ice quakes (concussions as a result of ice breakup), and will attempt to transmit that data from the base station via Wi-Fi, using a Wi-Fi antenna mounted at a neighboring Icelandic farm. In addition, the project's principal investigators—Kirk Martinez, a professor in the university's Department of Electronics and Computer Science, and Jane Hart, a geography professor at the college—deployed a similar system this month near Tijuana, Mexico, to monitor ground movement in an effort to predict future mudslides following heavy rains.
Martinez and his research team first began studying wireless sensor systems for monitoring glaciers in 2003, in Briksdalsbreen, Norway. He and Hart were seeking a system for remotely sending data about glacier dynamics throughout the year, without using cables, which typically snap under the pressure of heavy moving ice. Wireless sensors can move with the ice, and are thus more robust. The group drilled 260-foot-deep holes in the ice (the melting ice resulted in a subsequent annual loss of more than 30 feet of depth), and dropped the sensor probes inside. On the glacier's surface, they erected a base station, consisting of a computer wired to a transceiver, in order to receive transmission from the wireless sensor probes. The computer uses software designed by the researchers to interpret that information and transmit it via GPRS (the nearest cell tower is six miles away) to the Glacsweb software (also designed by the research team), operating on a server hosted by the University of Southampton.
While the scientists initially employed 868 MHz battery-powered wireless sensor probes, they were unable to transmit on warmer days through pockets of air and water. Therefore, they switched to using 433 MHz active transponders (utilizing proprietary transmission specifications), "which worked quite well," Martinez says. The sensor probes were designed to transmit a 100-milliwatt signal—powerful enough to pass through the ice and water and reach the base station. The system was still operating four years later, and had produced sufficient data for researchers to begin evaluating how much the glacier had moved and been reduced, and thereby proving the technology worked.
In summer 2008, the team took additional sensors and a base station to a colder, more challenging environment, at Skalafellsjökull. At that site, the glacier measures 328 feet deep and 30 miles in length. This time, the sensor probes transmitted at 173 MHz—by using the lower frequency, researchers were able to reduce the loss of transmission through scattering and reflection—again using a proprietary standard. Like the probes utilized in Norway, these included temperature sensors, accelerometers, electrical conductivity (to detect liquid water, as opposed to ice) and strain sensors. A GPS receiver mounted on the base station itself (which stood on the ice, above the probes) provides data indicating the direction and speed of the glacier movement. The probes and GPS receiver take hourly readings of latitude, longitude and sensor data, including temperature, movement (such as tilting and turning) and pressure, then transmit that data once daily, at around noon.
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