Height of sophistication

Cardiff University in partnership with geophysical consultant Terradat is investigating new techniques for quickly assessing areas most at risk from landslides.

Using a combination of helium balloons with digital cameras and GPS-controlled high resolution geophysical surveying methods, the team of researchers has been collecting data from areas in South Wales to create 3D computer models of landslides. By taking repeated measurements, the models can then be put together in an animation to show how a land mass has moved over time.

'The problem with a landslide is you need to get into a position where you can actually look down on it. Ideally you need a helicopter or an aircraft, but that can prove very expensive,' said Cardiff's Dr Peter Brabham. 'The cheaper option is to dangle a digital camera from a helium balloon on a long rope so you can wander slowly and carefully across a landslide. And because it is much lower, it gives you more resolution on the ground as well.'

The camera can be linked remotely to the ground or be set to take overlapping photographs every 10 or 20 seconds over an area. This produces 20 to 30 photographs, depending on the size of land being mapped. The photographs are then processed by Topcon software to develop a 3D model of the landslide.

To make this photographic image more meaningful and to allow the researchers to create a true scale 3D model, they first of all laid down dinner plate-sized markers randomly and surveyed them using high resolution GPS to plot the positions to the centimetre. These markers were then labelled with numbers that could be seen by the camera from above, with the aim of getting four markers into each photograph.

The 3D model of the landslide is further enhanced by information about how much water is percolating through it over time.

'We are using things such as electrical geophysical methods to look at the water in the landslide, which is fitted with permanent electrodes. By putting electrical currents through it, you get an electrical picture, or cross-section, which is affected by water content,' said Brabham.