Ground-based geomatic surveys

Basic terrestrial LiDAR scanning technique.

Geomatics is the science of gathering, storing, processing and delivering spatially related information. BGS has pioneered the use of ground-based (terrestrial) techniques for a variety of geoscientific applications since 1999. They have been used on a variety of projects such as the monitoring of actively growing volcanic lava domes and rapidly retreating glaciers, coastal erosion and platform evolution, inland and coastal landslide modelling, mapping of geological structures and fault boundaries, rock stability and subsidence feature analysis, creation of surrogate outcrop models for oil field reservoir rocks, and even geo-conservation projects, such as archiving and analysis of important outcrops, quarries and other temporary exposures.

As a tool of modern geoscience it allows unprecedented resolution and accuracy.


Geo-conservation of Hutton's Unconformity.

BGS uses Riegl and Faro terrestrial LiDAR scanners because of their flexibility, range and portability. We have a very long-range scanner that can make measurements at distances of over 2000 m, a medium-range scanner that can make accurate measurements at distances of up to 800 m and a high-speed, short-range (300 m) scanner that can take measurements at a rate of 972 000 points per second with an accuracy of ±3 mm. Our newest model is a Riegl VZ-1000 which can scan up to 1400 m with an accuracy of ±8 mm and a measurement rate of 62 000 points per second. A high-resolution digital camera coupled with a Leica differential GPS system enables coloured point-clouds, textured triangulated surfaces or orthophotos, with depth information, to be captured, accurately geo-referenced and processed. Modern laser scanners have significantly increased the level of resolution and accuracy achievable, and the speed of data acquisition.

The ability to capture and measure changes in geological features with time by repeat surveys has revolutionised ground-based geomatic research.

Installation of on-ice satellite positioning system. Virkisjoekull, Iceland.
3-D virtual outcrop model of a quarry created from coloured point-clouds and triangulated surfaces.

Tracking glaciers' retreat

Surveying set-up deployed on the glacial foreland. Falljoekull, Iceland.

By using a combination of repeat terrestrial LiDAR scanning (TLS) surveys, on-ice based global navigation satellite systems (GNSS) and ground penetrating radar (GPR) we have been able to see the full picture of glacial retreat for the first time. This work has shown that the margin of the Falljökull glacier, in south east Iceland, has ceased moving and is now undergoing stagnation. However, field and photographic evidence shows that the icefall remains active, feeding ice from the accumulation zone on Öraefajökull to the lower reaches of the glacier. To accommodate this continued forward motion, the upper section of the glacier below the icefall is undergoing intense deformation (folding and thrusting) and as a result, is being thrust over the lower, immobile section of Falljökull. This type of behavior has never been described before and could have implications for how other steep mountain glaciers around the world are responding to changes in the climate.

Monitoring shifting coastlines

Multiple landslide slumps and embayment development. Aldbrough, North Yorkshire.

We use our laser systems to monitor actively eroding sections of coast around England. The techniques we have developed are ideal for this application as TLS is particularly suited to measuring vertical cliff sections. Measurements from a plane or satellite measure only the top edge of the cliff, whilst measuring them in the field is often very dangerous. Our technique enables the measurement of changes in the whole cliff section from a safe distance, which can be used to model how internal processes within the cliff slope affect coastal erosion. Our work at Aldbrough in North Yorkshire has shown that the cliff is disappearing at an average rate of up to 3 m per year; this erosion is caused by both landslides and the direct action of the sea crashing against it.

Measuring active volcanoes

Terrestrial LiDAR scanning of the lava dome. Soufriere Hills volcano, Montserrat.

There can be few more hazardous situations than that of monitoring a volcanic andesite lava dome for signs of an impending collapse. Partial collapse of a lava dome generates hot, fast-moving pyroclastic density currents. Monitoring in such circumstances requires that measurements are taken from a distance that minimises the threat from eruption and from asphyxiation by volcanic gases. The method also needs to be rapid, to minimise the time spent by the monitoring team in the hazardous zone. We have used TLS techniques to monitor the growth of the lava dome on Mount Soufrière on the Caribbean island of Montserrat. In May 2006, our measurements helped to support the decision to declare a volcano alert and evacuate the people of nearby villages and towns.

Contact

For further information please contact Lee Jones.