Ground-based geomatic surveys

Geomatics is the discipline of electronically gathering, storing, processing and delivering spatially related digital information. This broad term applies to both science and technology, and integrates the more specific disciplines and technologies of geodesy, surveying, mapping, positioning, navigation, cartography, remote sensing, photogrammetry and geographic information systems (GIS).

Geomatics at the BGS

Geoconservation of Hutton's Unconformity.

The BGS has pioneered the use of ground-based (terrestrial) techniques for a variety of geoscientific applications since 1999. These have been used on a variety of projects such as:

  • monitoring of actively growing volcanic lava domes
  • monitoring of 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
  • geoconservation projects, such as archiving and analysis of important outcrops, quarries and other temporary exposures

In fact, the BGS has carried out over 300 surveys at more than 150 sites, both in the UK and overseas.

Terrestrial LiDAR scanning

Basic terrestrial LiDAR scanning technique.

As a tool of modern geoscience, the use of terrestrial LiDAR scanning (TLS) allows unprecedented resolution and accuracy.

The BGS uses Riegl and Faro terrestrial light detection and ranging (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 the 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 global navigation satellite system (GNSS) enables coloured point clouds, textured triangulated surfaces or orthophotos, with intensity and depth information, to be captured, accurately georeferenced and processed.

Modern TLS systems 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 satellite positioning system
3D virtual outcrop model of a quarry

Mobile mapping solutions

Hollin Hill, Yorkshire.

The BGS has become one of the first organisations in the UK to purchase the Leica Pegasus Backpack, a wearable reality-capture sensor platform. The backpack combines five 4 MP cameras, offering a fully calibrated 360° × 200° view, with two 16-channel LiDAR profilers, capable of scanning 600 000 points per second at a range of 50 m, and a triple band GNSS and inertial measurement unit (IMU), capable of a positional accuracy of 20 mm, in an ultra-light carbon fibre chassis weighing 13  kg.

The Pegasus Backpack offers great speed and portability advantages over existing TLS systems, which can weigh in excess of 30 kg and are extremely bulky to carry, enabling the BGS to carry out 3D mapping of long coastal or inland sections; landslides and other unstable surfaces; ice sheets and glaciers; railway lines; roads, and other linear features.

The BGS can carry out building information modelling (BIM) using both imagery and point-cloud data to document outdoor, indoor and even underground areas. Disaster responders will be able to capture data in 3D, on foot, in danger-zone areas. Simultaneous localisation and mapping (SLAM) technology and a high-precision IMU ensure the achievement of accurate positioning even during GNSS outages, and with the addition of the external light source, precise scanning of tunnels and cave systems is possible. The backpack can also be vehicle mounted, for mobile mapping, or pole mounted, for lowering into voids or sinkholes. This system allows for faster capture of critical data, leading to better-informed decisions, on site if necessary.

Tracking glacial retreat

Surveying set-up in Iceland

By using a combination of repeat TLS surveys, on-ice-based 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 behaviour 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. Because of this Falljökull glacier has been called the 'zombie' glacier.

Monitoring shifting coastlines

Landslides, Aldbrough, 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 the East Riding of Yorkshire, has shown that the cliff is disappearing at a rate of three metres a year; this erosion is caused by both landslides and the direct action of the sea crashing against it.

Measuring active volcanoes

Terrestrial LiDAR scanning Soufriere Hills

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.

External links