Investigations on surface reflection models for intensity normalization in Airborne Laser Scanning (ALS) data

The analysis of laser scanner data is of great interest for gaining geospatial information. Especially for segmentation, classification, or visualization purposes, the intensity measured with a laser scanner device can be helpful. For automatic intensity normalization, various aspects are of concern, like beam divergence and atmospheric attenuation, both depending on the range. Additionally, the intensity is influenced by the incidence angle between beam propagation direction and surface orientation. To gain the surface orientation, the eigenvectors of the covariance matrix for object points within a nearby environment are determined. After normalization the intensity does no longer depend on the incidence angle and is influenced by the material of the surface only. For surface reflection modeling, (a) the Lambertian, (b) the extended Lambertian, and (c) the Phong reflection model are introduced, to consider diffuse and specular backscattering characteristics of the surface. An airborne measurement campaign was carried out to investigate the influences of the incidence angle on the measured intensity. For investigations, 17 urban areas, such as traffic, building, and vegetation regions were studied and the derived improvements are depicted. The investigation shows that large intensity variation caused by the object surface orientation and the distance between sensor and object can be normalized by utilizing the standard Lambertian reflection model.