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A. Roncat, P. Dorninger, G. Molnár, B. Székely, A. Zámolyi, T. Melzer, N. Pfeifer, P. Drexel:
"Influences of the Acquisition Geometry of different Lidar Techniques in High-Resolution Outlining of microtopographic Landforms";
Talk: Fachtagung Computerorientierte Geologie - COGeo 2010, Salzburg; 2010-06-11; in: "Fachtagung Computerorientierte Geologie - COGeo 2010", (2010), 17 pages.

In the past 15 years, Airborne Laser Scanning (ALS) has become a core technology for the acquisition of 3D topographic data. Laser scanning is also referred to as Lidar (Light Detection and Ranging). Terrestrial laser scanning (TLS) has proven to be capable to deliver results comparable to those of ALS in both resolution and accuracy for small areas, too.

Although the operating principles of these two techniques are similar, the acquisition geometries of ALS and TLS differ in some important details: First, in the case of ALS the laser beam is directed nearly perpendicularly to the ground. In contrast to this, in TLS the direction of the laser beam might be nearly parallel to the terrain or not even hitting it. Second, ALS is always dynamic (each point is recorded from a different position) whereas TLS is mostly static, i.e. the sensor is mounted on a tripod and remains at a fixed place during the scan. The results of these differences are e.g. a higher dynamic range of TLS compared to ALS caused by the broader interval of the targetsī distances and a higher variation of incidence angles in TLS. Moreover, vegetation - if regarded as an "obstacle" between the scannerīs position and the terrain - has to be treated with in different ways for ALS and TLS, respectively.

In this article, we analyse the effects of the points mentioned above on the results of ALS and TLS regarding geomorphologic and topographic purposes, focusing on the derivation of digital terrain models (DTMs) as well as on filtering and classification of point clouds. Results indicate that surface processes follow and reveal microtectonic features. However, geologic mapping and analysis defining the surface processes typically record structural geologic information at a much
larger scale. The additional point-wise field observations, such as dip directions, dip values, and displacement measurements along slickensides, are generally scattered and scarce. By combining the geologic information with the high-resolution ALS and TLS data, the needed detail for the assemblage of continuous, micro-scale geologic datasets suited for the current analysis can be provided. Empirical evaluation is carried out by means of the data recorded at the Doren landslide (Vorarlberg, Western Austria). For this area, multi-temporal data sets of both ALS (March and December 2007) and TLS (September 2008 and August 2009) are available. This area is situated in the Molasse Zone characterized by various clays, sandstones, and calcareous sandstones. The relief is hilly to mountainous due to the combined effects of the relatively high erodibility of the rocks
and the post-glacial surface evolution of the area. Thus, this region provides an ideal training area for the analysis of influences on the acquisition geometry.

http://dx.doi.org/10.5242/cogeo.2010.0008

http://www.cogeo.at/publications/cogeo2010/cogeo2010_0008.pdf