In: Wagner W„ Sz^kely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
objects (e.g. cars, buildings, individual trees, or brushwood) 
within the point-cloud. 
In any case, sophisticated classification is necessary. For the 
extraction of a DTM, various algorithms were developed (cf. 
Briese, 2010). All of them have in common that they study the 
local geometric properties of the acquired ALS points. Other 
information, which could help to improve classification, is 
rarely utilized. 
With the advent of full-waveform (FWF)-ALS systems (Hug et 
al. 2004, Wagner et al., 2004) additional interesting observables 
for an advanced classification of the FWF-ALS data have 
become available. Doneus and Briese (2006) demonstrate the 
advanced capabilities of FWF-ALS data for the generation of 
digital terrain models (DTM) in vegetated areas. The echo width 
determined from the FWF information was used to support the 
classification of the ALS data into terrain and off-terrain points 
in the presence of low vegetation. Miicke (2009) extended the 
utilisation of the echo width by introducing a weighting scheme 
that depends next to the increase of the echo width on the echo 
amplitude. In both examples, utilizing information from FWF- 
ALS could improve the quality of the estimated DTM. 
FWF-ALS therefore seems to be a very promising approach to 
enhance the quality of both DTMs and digital object models 
(DOM). However, it is still in its infancy. In contrast to 
conventional ALS sensors FWF-ALS is just available since a 
few years and extended processing chains still have to be 
developed. Especially the complex interaction of the laser beam 
with different types of vegetation cover has to be better 
understood. Enhanced knowledge in this field, i.e. an in-depth 
understanding of the FWF-information will improve both 
quality and reliability of DTMs. This is especially desirable in 
areas with low vegetation. Furthermore, the investigations 
should lead to advanced geometric models that allow a more 
reliable automated analysis, which is desirable for different 
applications (hydrology, etc. as well as archaeology). 
This paper can be seen as a first step towards a detailed study of 
the interaction between FWF-laser beams and various objects 
within a vegetation complex. For the analysis a vegetated area 
was simultaneously scanned by airborne and terrestrial (TLS) 
laser scanning on a calm day. After presenting the study area, 
we will focus on the process of co-geo-referencing the ALS and 
TLS data sets. In section 4 and 5, some preliminary results of 
the analysis of the FWF-ALS data set are presented and 
discussed. 
2. STUDY SITE AND DATA ACQUISITION 
For the study of the FWF-ALS data, a small area (approx. 
2.25km 2 , cf. Figure 1) was selected in the Leithagebirge, 
approx. 30km south of Vienna. This area is already well known 
by the authors due to a small FWF-ALS mission in 2006 
(Doneus and Briese, 2006) and a large archaeological FWF 
ALS data acquisition campaign carried out in 2007 (cf. Doneus 
et al, 2008). It contains a large building complex of a former 
monastery (“St. Anna in der Wüste”) in the central northern 
part. The buildings are encircled by an open meadow which is 
enclosed by a forest with understory of varying density. 
Figure 1. Study Site “St. Anna in der Wüste” in the area of the 
Leithagebirge (30km in the south of Vienna) with the planned 
flight lines (approx, length: 1.5km) for the ALS data 
acquisition. © Google 2010 
Figure 2. Left: Shading of a digital surface model (DSM, 
0.25m raster) of the main area of interest (370m by 370m) 
derived from the ALS data; Right: DSM shading and TLS data 
(red). 
The data acquisition of the site took place on the 10 th of 
December 2009 in leaf off condition. It was a day with no wind. 
This was important to exclude the effect of wind on the 
vegetation canopy and facilitate the co-registration of the 
simultaneously performed TLS and ALS scans. The FWF-ALS 
data set was acquired during a test flight of the company RIEGL 
Laser Measurement Systems GmbH with the novel FWF-ALS 
sensor RIEGL LMS-Q680 (Riegl, 2010). The area was covered 
by six strips (both three strips in perpendicular directions) with 
a flying height of approx. 500m above ground. This resulted in 
an ALS point density of approx. 20 last echo points/m 2 . A 
shading of the resulting digital surface model is displayed in the 
left part of Figure 2. 
The TLS data acquisition took place simultaneously to the ALS 
flight. The TLS data was acquired by a Riegl VZ-400 
instrument with online waveform processing capability (cf. 
Riegl, 2010; Pfennigbauer and Ullrich, 2010). Additionally to 
the TLS data, images were acquired by an attached digital 
camera (Nikon D300). Altogether, data from 16 stations were 
acquired near the north eastern part of the monastery (cf. right 
part of Figure 2). For an advanced geo-referencing of the ALS 
and TLS data (see section 3), some of the stations covered the 
monasteries’ inclined planar roof areas with different 
exposition. Furthermore, reflector targets were used in order to 
perform a relative orientation/registration of the individual 
stations. 
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