Landscape change | Terrestrial LiDAR

Riegl LPM800 terrestrial LiDAR
Extract of change model 2009/2010 derived from LiDAR digital elevation models
LiDAR in use near the margin of Virkisjokull

Spanning more than a decade, photographic and volumetric evidence clearly demonstrate that Oraefajökull’s outlet glaciers are now smaller than at any time in the last 100 years, and are shrinking at an increasing rate — faster than at any time in the last 100 years.

Marked changes in the size and shape of Virkisjökull have taken place since 1996 when the glacier was in good health. These changes have been most dramatic in the last seven years.

In the last 15 years it is estimated that over 1 km of horizontal recession and 65 m of vertical thinning has taken place at this glacier. To put this in perspective, the glacier has only retreated around 1 km and thinned about 50 m in the previous 100 years combined.

Terrestrial LiDAR: Laser scanning and landscape change

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 the landscape around the glacier.

Using several scans made at different times, we can accurately calculate both ice volume change and glacier retreat, as well as rates of landscape evolution. We can also get far more information about how the glacier or surrounding landscape is changing than is possible from traditional levelling or photographic techniques.

The LiDAR is placed on a tripod and positioned using the GPS, the user then defines a scan area and sets it going. The Riegl LPM i800AH we have used up to now is able to capture 1000 points per second, all precisely positioned in x, y and z relative to the scanner position. Over about 20–30 minutes the LiDAR will capture 1–2 million scan points on the landscape. Completing several scans from different positions allows us to gather scan points from all over the landscape — termed a 'point cloud'. As the scanner has a digital camera attached, each of these points can be given a 'real' colour — see Virkisjökull terrestrial LiDAR point cloud animation, 2010.

From the point cloud a very accurate Digital Elevation Model (DEM) can be created, which shows a realistic landscape surface. By repeating scans we can subtract one from another to see what has changed and by how much. These are called Change Models, and are extremely valuable in being able to show rates and amounts of landscape change. By comparing these changes with the climate data and our other datasets, we can start to discover the linkages and driving forces behind landscape and glacier evolution.

Contact

Contact Jez Everest for further information