Utilizing Airborne Laser Altimetry for the Improvement of Automatically Generated Dems over Urban Areas

Airborne laser altimetry is a highly efficient and accurate method of obtaining data for the determination of visible surface topography. With minimal processing, the laser data can provide coordinates of points on the visible surface with high spatial frequency and precision. Although this technology has benefits compared to photogrammetric techniques, there are limiting factors due to the laser data having no thematic information. These limitations may be overcome by utilizing aspects of both laser altimetry and photogrammetry in the surface determination process. The research described in this paper has been undertaken to accurately determine the visible surface in urban areas using airborne laser scanner data and digital aerial images. In this research, edges detected in the aerial images are used to refine the digital surface model (DSM) produced from airborne laser scanner data. The three dimensional edge information allows improvement of the laser DSM by providing accurate horizontal locations of the surface discontinuities. Therefore the laser data and the edge information are merged to obtain the benefits of each data set, facilitating the generation of an accurate surface model. The paper presents preliminary results of testing undertaken using an algorithm developed to combine laser data and photogrammetric data. The data set used in the testing is an urban site covering Ocean City, Maryland, USA.