Height Information from Laser-Altimetry for Urban Areas

The need for height information for approaching urban problems has grown rapidly the last decade. The needs include design and inspection of utilities such as water mains, sewer systems, tunnels, bridges, roads, railroads and power lines, and the creation of 3-dimensional digital city models, in which the shape of buildings and other objects have been reconstructed with high spatial detail, for city planning and development purposes. In the past, one could usually suffice with contour lines. At present, the demands with respect to accuracy and level of detail are far beyond this point. In addition, the processing of huge amount of data requires automation. New remote sensing techniques have emerged which are able to respond to these demands. They include Laser-altimetry, matching of stereo pairs of imagery and radar-based systems (INSAR). They sample the terrain blindly by automatic means, while being able to carry out data capturing with high point density. In particular, Airborne Laser-altimetry Systems (ALS) have many beneficial properties. The automation rate is large, while time-efficiency and cost effectiveness are high. This paper examines the suitability and possibilities of ALS for fulfilling parts of the height information needs in urbanised areas. Our considerations are partly based on an inventory study about height needs carried out among local authorities in the Netherlands. The local authorities involved cover both small and large cities. Our overview is interesting for many involved in urban planning, design, inspection and monitoring