Lateral image degradation in terrestrial laser scanning

The use of aerial laser scanning to detect change in infrastructure and buildings after major disasters has become increasingly common in recent years to help prioritize interventions. More recent efforts are being invested to apply laser scanning in the assessment and structural health monitoring of buildings to simplify and quicken building damage surveys by the automatic detection of defects and deformations. Technology application must, however, be done in cognizance of equipment constraints regarding scan angle, sampling size, and beam width. This article reports a series of laboratory and field experiments designed to begin to quantify and minimise the possible errors for effective defect detection via terrestrial laser scanning during surveying. Varying geometric positions that cause either over- or under-prediction of crack thickness and length as a function of both standoff distance and angle of obliquity between the scanner and the defect are presented. These may over-predict horizontal crack thickness by 15 mm and failing to detect others. To help minimise such errors, a standoff distance of 12–15 m with a maximum obliquity of 45˚ between the scanner and target object are recommended.