Analysis of the Backscattered Energy in Terrestrial Laser Scanning Data

Terrestrial laser scanning provides a point cloud, but usually also the “intensity” values are available. These values are mainly influenced by the distance from sensor to object and by the object’s reflection properties. We demonstrate that it is possible to retrieve these reflection properties from the observed range and the intensity value. An experiment with targets of known reflectivity behaviour is described. Retrieving object reflectivity is also demonstrated for these targets in another experiment, which was not used to determine the functional relationship between range, reflectivity, and intensity. The Lidar equation describes the received optical power in terms of the emitted power, range, and target properties. Nonetheless, the intensity values do not follow this prescribed behaviour. Therefore, data driven approaches are used, allowing a better prediction of the observed intensity from the range and reflectivity of the targets. For a Riegl LMS-Z420i and an Optech ILRIS 3D these experiments were performed. Both scanners measure range by the travel time of a pulse. In our experiments, the reflectivity can be estimated from the laser scanning data with a standard deviation of 6% or better. This demonstrates the potential for retrieving material properties of natural surfaces, too.