In: Wagner W., Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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ANALYSIS OF FULL-WAVEFORM ALS DATA BY SIMULTANEOUSLY ACQUIRED 
TLS DATA: TOWARDS AN ADVANCED DTM GENERATION IN WOODED AREAS 
M. Doneus a,b *, C. Briese a,c , N. Studnicka d 
a Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Vienna, Austria - 
Michael.Doneus@archpro.lbg.ac.at, Christian.Briese@archpro.lbg.ac.at 
b Department for Prehistoric and Medieval Archaeology, University of Vienna, Austria 
c Christian Doppler Laboratory for Spatial Data from Laser Scanning and Remote Sensing, Institute of Photogrammetry 
and Remote Sensing of the Vienna University of Technology, Austria 
d RIEGL Laser Measurement Systems GmbH, Austria - nstudnicka@riegl.co.at 
Commission VII 
KEY WORDS: Laser scanning, LIDAR, full-waveform, Aerial, Terrestrial, Combination, Analysis, Archaeology 
ABSTRACT: 
Airborne laser scanning (ALS, also referred to as airborne LIDAR) is a widely used data acquisition method for topographic 
modelling. In archaeology, it has revolutionised prospection of forested areas. Here, especially full-waveform (FWF) ALS systems 
show considerable advantages for the generation of digital terrain models (DTM) in vegetated areas, as the FWF-information (e.g. 
echo width) can improve classification of ALS data into terrain and off-terrain points, resulting in greater DTM quality and higher 
potential for the subsequent archaeological interpretation. FWF-ALS displays a high potential, but is still in its infancy (in contrast to 
conventional ALS sensors FWF-ALS is just available since a few years). One key topic to be investigated is the complex interaction 
of the laser beam with different types of vegetation cover. An in-depth understanding of the FWF-information is essential to enhance 
the quality of the DTM and to allow a reliable automated interpretation of the acquired data. To study the interaction of ALS and the 
resulting FWF-information with a vegetation complex, part of a forest was scanned by airborne and terrestrial laser scanning (Riegl 
LMS-Q680 and Riegl VZ-400). The combined data acquisition took place simultaneously on a calm day. Using tachymetry, the data 
sets were geo-referenced and the differences between the ALS and TLS data sets were minimized by an adjustment using planar 
control and tie patches. Based on the TLS dataset, the position of the derived ALS echoes are studied and the additionally derived 
FWF-parameters are investigated. This analysis allows increasing the knowledge about the interaction of the laser beam with 
different surface elements and allows to estimate the potential for methods for advanced DTM generation. Based on this knowledge a 
high quality DTM can be determined which allows an advanced interpretation of archaeological structures which are present on the 
terrain surface. 
1. INTRODUCTION 
In the last years, airborne laser scanning (ALS, also referred to 
as airborne LIDAR (light detection and ranging)) became a 
widely used data acquisition method for sampling of the 
topography. The resulting 3D data provides a good basis for 
modelling the ground surface with or without objects (houses, 
trees) and is utilized in several different application areas, e.g. 
hydrology (Mandlburger et al., 2009), city modelling 
(Rottensteiner and Briese, 2002) and forest mapping (Naesset, 
2007). ALS especially excels in forested areas due to the fact 
that an active direct 3D sensing principle is utilized (for the 
estimation of one point on the illuminated surface only one line 
of sight is necessary). Small footprint ALS systems can 
penetrate the vegetation layer through small gaps in the canopy 
and therefore may allow receiving an echo from the terrain 
surface even in densely vegetated areas. 
This advantage of ALS in vegetated areas and furthermore the 
increasing capabilities of ALS sensor systems (increasing point 
density with more than 1 point/m 2 ) has also revolutionized 
archaeological prospection of forests. Due to the availability of 
country wide ALS data the study of extended archaeological 
landscapes becomes possible. However, to successfully apply 
ALS for archaeological prospection, special demands have to be 
met during data analysis (Doneus and Briese, 2010). 
After geo-referencing of the acquired observations, the result of 
an ALS data acquisition campaign is a (strip wise) unstructured 
and unclassified 3D point cloud (often enriched by additional 
attributes like echo ID, echo intensity or amplitude, GPS time, 
etc.). This point cloud can be utilized for visualisation purposes, 
but for an advanced use of the data there is usually the need for 
further analysis and classification. All of the application areas 
mentioned have typically in common that a classification of the 
ALS data into terrain and off-terrain points is essential. 
For archaeological prospection, the terrain points and the 
resulting digital terrain model (DTM) are of vital importance. 
Here, the separation into surface and object points has to be of 
high quality, because errors can easily lead to misleading 
interpretations. Other applications, like city modelling, biology 
or forestry are especially interested in the identification of 
* Corresponding author.