Terrestrial Laser Scanning

A powerful surveying method, critical to the CHERISH survey teams working on the ground will be Terrestrial Laser Scanning (TLS). This was technique was developed towards the end of the 20th Century, largely to undertake as-built surveys of complex industrial complexes. The operating principle of TLS is based on measuring the time of the return signal of a laser emitted from the instrument and reflected from the surface being measured. As such, they are contact-free measuring devices that can record objects in the form of dense point-clouds of objects.

Depending on the particular instrument, high precision geometric data can be gathered rapidly over a range from 0.5 – 300m. After processing each point is assigned with X, Y, Z coordinates, colour and reflectance value. A point-cloud example of Gallarus oratory, generated by the Discovery Programme is shown in Figure 8. With a resolution of approximately 5mm, typical of TLS surveys, the fine architectural detail is revealed at a stone by stone level. The value of such data is immense; documentation at this resolution highlights irregularities associated with most historic structures that have the potential to unravel phasing for researchers or indicate conservation issues such as crack lines or slumping.

Intensity shaded view of the point cloud of Gallarus Oratory, Co Kerry, surveyed by TLSIntensity shaded view of the point cloud of Gallarus Oratory, Co Kerry, surveyed by TLS.

CHERISH survey teams have access to two FARO Focus instruments, a Focus 120 and Focus 330. The aim will be to use these to gather baseline data of vulnerable and actively eroding archaeological sites. This data, in the form of a high resolution point cloud, will be available for comparison with subsequent surveys throughout the duration of the project. Point cloud comparison software will be used to identify and then quantify any changes that have taken place.

Coastal survey using Faro Focus 3D terrestrial laser scannerCoastal survey using Faro Focus 3D terrestrial laser scanner