|COLOR CODED Fissures can develop on rims of sinks. (Photo courtesy of AMEC Earth & Environmental)|
The European Space Agency has awarded a U.S. firm $878,000 to develop projects to demonstrate satellite technology to monitor large-area ground subsidence, which can damage linear infrastructure such as rail lines, pipelines, canals, sewers and roads.
"The European Space Agency wants more exposure of the technology to potential users," says Ralph Weeks, senior geologist with contract recipient, AMEC Earth and Environmental, Phoenix, Ariz. "We can make the transfer between raw technology and its application for clients."
The technique involves comparing radar data acquired in two satellite passes over a study area, usually separated by months or years. Ground elevation changes are revealed and can be mapped in 2D or modeled in 3D.
On the 2D maps, or interferograms, centimeters of movement are shown as color shifts. Bulls-eye patterns represent bowls of rapid subsidence. In the example shown from an area near Phoenix, for instance, any color cycle, such as from one cyan band to the next cyan band, reveals 3 centimeters of vertical change over a two-year period. "This gives you a perspective that was not possible before," says Weeks.
ESA asked AMEC to develop projects because the agency literally has a world of archived data, but needs to educate customers on how it can be used.
|(Photo courtesy of AMEC Earth & Environmental )|
The Phoenix area has two large basins where groundwater extraction is causing severe subsidence. Gravity-fed sewer and water distribution systems are affected. There are serious concerns about pipelines and other infrastructure as well. Earth fissures can develop at the fringes between a dropping area and a stable one. Cracks can breech or destabilize dams, canals and other structures.
"Its a quiet hazard," Weeks says. "Most of the time the subsidence is a slow process, kind of like ulcers. It has a grinding effect on things."