Terrestrial Laser Scanning: Imaging, Quantifying, and Monitoring Microscale Surface Deterioration of Stone at Heritage Sites

Documentation is a valuable tool for preserving heritage resources. As new digital recording devices emerge, it is incumbent on heritage professionals to thoroughly evaluate them in order to identify their strengths, weaknesses, and appropriate uses. This paper describes an application of in situ terrestrial laser scanning that tests its practicability for use as a recording tool for conditions surveying. Two lion sculptures at the Merchants' Exchange Building in Independence National Historical Park, Philadelphia, Pennsylvania, were scanned using a midrange, time-of-flight terrestrial laser scanner. A condition survey was performed and conditions were mapped onto digital 3D models created from the scan data. These models were used to evaluate patterns of deterioration, identify their causative factors, and communicate those deterioration pathologies to site managers.

A second area of research presents the investigation of the feasibility and necessary parameters of using terrestrial laser scanning to monitor microscale surface deterioration of stone objects. Three issues are described: the relationship between single-point error and point cloud resolution; how resolution and rate of deterioration affect the monitoring time frame; and how materials and environmental conditions affect the accuracy of the scan data.