Detecting impending landslides from the air is difficult when the signs of them are hidden under the canopy of forests or the changes in the soil are very small. On site – when climbing on the slope – one would be able to see the harbingers of the landslides well, but the endangered areas are large and inspection visits are therefore time-consuming. That is why Fiona Muirhead is working at the aeronautical engineering company Leonardo on a radar device for helicopters and small aircraft that can look through the dense foliage and also measure small changes with high resolution.
If the Scottish aeronautical engineer uses the synthetic aperture radar interferometer (SAR) to systematically scan a search area twice using the same pattern, tiny differences in the two images produce a high-resolution elevation relief of the ground. Comparisons between control flights can reveal suspicious changes in altitude and thus give indications of impending landslides and subsidence. Slightly elevated water levels could in turn be warning signs of flooding. These areas can then be examined more precisely on site.
“Until now, such analyzes have been done with satellite radar measurements because they can cover larger areas,” says Muirhead. This satellite monitoring is relatively cheap and can also see the terrain under the canopy, “but it provides a coarser resolution and does not see minor changes in the elevation”. A higher frequency range than that of satellites is necessary for a more precise measurement. In addition, one has to wait for the satellite’s overflight window, while flights close to the ground are also possible at short notice.
Affordability still uncertain
In order to rule out artifacts caused by blurred images, Muirhead’s device uses sensors to measure the movements of the aircraft and then calculate them out. “That delivers a smooth, sharp image,” says the engineer. Tests to date have shown that the measurements are good for making predictions.
Her employer Leonardo does not yet want to reveal what the technology would cost. The goal is to make them affordable for civil authorities. He is already in talks with several infrastructure authorities and companies. For example, the not-for-profit company Network Rail, which owns all of the UK’s rail infrastructure, is interested in SAR technology. It is already monitoring the area around tracks with helicopters and drones and is working on remote monitoring technologies itself.
If authorities and companies can use their own helicopter fleet, the use of the mobile SAR system would be cheaper than chartering extra aircraft, says Leonardo. The use of such compact sensors is now almost as easy as mounting a flight camera on a helicopter.