Terrestrial Light Detection and Ranging (LiDAR) is a land-based laser scanner which, combined with a highly accurate differential GPS, enables us to produce 3D computer models of landslides at the coast (The LiDAR).
Using several scans made at different times, we can accurately calculate volume change and cliff top recession rates. We can also get far more information about how the cliff or landslide is changing than is possible from traditional levelling or photographic techniques.
To make a survey, the team sets up the equipment on the beach in front of the eroding cliff line, or from another vantage point (depending on weather and tidal conditions), and scans a swathe of cliff up to 800 m in width. Scans typically take up to 20 minutes, collecting 2000 individual measurements of the cliff face per minute from a distance of 100–150 m. The data collected in the field by laser scanning and GPS are entered into a modelling package.
As part of a programme of work monitoring coastal erosion and landsliding we are surveying several sites around the coast of Great Britain (see map).
The sites were originally selected to represent mostly unprotected cliffs with 'soft' geology so change could feasibly be measured within the timescales of the project. The sites also have a range of landslide types and sizes.
Some of the 12 sites have been monitored only for a short period before being discontinued or postponed due to inactivity or funding restrictions, but about half of them are being actively surveyed.
Satellite imagery can be used to analyse and make measurements of ground movement such as landslides. However satellite imagery is less useful at the coast for two main reasons:
We use terrestrial LiDAR as a tool to fill this gap.
Studying and, in particular, measuring landslide and cliff movements on the ground can be very dangerous. Using terrestrial LiDAR means that accurate measurements can be made from a safe distance.
The technique is also cheaper to operate and technically simpler than photogrammetry.
Terrestrial LiDAR has been used for a variety of applications such as the monitoring of volcanoes (Hunter et al., 2003; Jones, 2006), earthquake and mining subsidence, quarrying, buildings, forensics (Paul & Iwan, 2001; Hiatt, 2002) and terrestrial- (Rowlands et al., 2003) and coastal- (Hobbs et al., 2002) landslide modelling.
Disappearing Coasts - A case study at Happisburgh - Planet Earth - PDF
Coastal Cliff Monitoring - the pros and cons of terrestrial LiDAR techniques - GeoConnexions - PDF
Hiatt, M.E. (2002). Sensor Integration Aids Mapping at Ground Zero. Photogrammetric Engineering and Remote Sensing, 68, 877-879.
Hobbs, P., Humphreys, B., Rees, J., Tragheim, D., Jones, L., Gibson, A., Rowlands, K., Hunter, G. & Airey, R. (2002). Monitoring the role of landslides in 'soft cliff' coastal recession. In: Instability Planning and Management. (Eds, McInnes, R.G. and Jakeways, J.) Thomas Telford, Isle of Wight, 589-600.
Hunter, G., Pinkerton, H., Airey, R. & Calvari, S. (2003). The application of a long-range laser scanner for monitoring volcanic activity on Mount Etna. Journal of Volcanology and Geothermal Research, 123, 203-210.
Jones, L.D. (2006), Monitoring landslides in hazardous terrain using terrestrial LiDAR: an example from Montserrat: Quarterly Journal of Engineering Geology and Hydrogeology, v. 39, 371-373.
Paul, F. & Iwan, P. (2001). Data Collection at Major Incident Scenes using Three Dimensional Laser Scanning Techniques. In: The Institute of Traffic Accident Investigators: 5th International Conference held at York. New York.
Poulton, C.V.L., Lee, J.R., Jones, L.D., Hobbs, P.R.N., and Hall, M. 2006. Preliminary investigation into monitoring coastal erosion using terrestrial laser scanning: case study at Happisburgh, Norfolk, UK: Bulletin of the Geological Society of Norfolk, 56, 45-65.
Rowlands, K., Jones, L. & Whitworth, M. (2003). Photographic Feature: Landslide Laser scanning: a new look at an old problem. Quarterly Journal of Engineering Geology, 36, 155-158.