An Empirical Method in Correcting Specular Highlight Phenomenon in TLS Intensity Data

Abstract

The intensity value recorded by terrestrial laser scanning (TLS) systems is significantly influenced by incidence angles. Most existing models focus on the diffuse reflection of rough surfaces and ignore the specular reflection, despite that both reflections simultaneously exist in all natural surfaces. At large incidence angles, specular reflection can be neglected. However, laser detectors can receive a portion of specular reflection at small incidence angles. Specular reflection can lead to additional increase in the original intensity data and even highlight phenomenon on scanned targets, especially those with a relatively smooth or highly reflective surface. In this paper, a new empirical method is proposed to correct the intensities of highlight regions caused by the specular reflection. The intensity from the specular reflection is obtained by subtracting the intensity caused by diffuse reflection and instrumental effects from the original intensity. The proposed method is tested and validated on different targets scanned by Faro Focus 3D 120. Results imply that the proposed method can effectively eliminate the highlight phenomenon in TLS for 3-D point cloud representation by intensity and intensity image interpretation.