Earth orbiting satellites are now able to determine areas prone to land subsidence, the sinking of ground above abandoned mines.
Age lies heavily on the abandoned mine shaft, its stale air thick and leaden in the darkness. Decades ago, it was a bustle of activity, with hunched men digging coal out of the blackened walls and carrying it to the surface about 10 metres above their heads.
Today, it sits empty and hollow as the supporting pillars begin to sag with each year. Tufts of grass have begun to grow above it, and many have forgotten that there was once a mine there, until one day the roof of the mine collapses and sucks the surface into its belly.
“Surface deformation due to underground mining poses risks to health and safety as well as infrastructure and the environment,” explained Dr Jeanine Engelbrecht this week. She recently completed her PhD at the University of Cape Town in techniques to detect mining-related land subsidence. “Sometimes mining companies are aware [of potential subsidence], but when they don’t expect surface subsidence, it can cause serious damage to infrastructure and roads.”
Meanwhile, an orbiting satellite is bouncing signals off the earth’s surface to detect where this will happen. Engelbrecht, now based at the Council for Scientific and Industrial Research’s ICT Meraka Institute, is using these data to predict possible subsidence on South Africa’s surface.
“We used earth orbiting satellites [transmitting and receiving] microwave signals to accurately measure the earth’s surface,” Engelbrecht said. For her PhD, she used this technique on an area that had been an underground coalmine, but cannot disclose which mine due to a confidentiality agreement. The data, captured by European, Japanese and Canadian satellites, can measure surface deformation in terms of millimetres.
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