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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
40, 
' 
101 102 103 104 105 106 107 201 2Ö2 203 204 205 
target number 
207 
Figure 10. Transformed vertical displacements of sphere 
centres between different loadings and initial 
situation measured by terrestrial laser scanner. 
3 0 
20 
VO 
0.0 
-30 
-4.0- 
PI - initial 
P2 - initial 
R3 - initial 
101 102 103 104 105 106 107 201 202 203 204 205 207 
target number 
Figure 11. Differences between transformed vertical 
displacements of TLS and precise levelling for 
different loadings. 
Mean 
residual 
(initial- 
Pl) 
[mm] 
Mean 
residual 
(initial- 
P2) 
[mm] 
Mean 
residual 
(initial- 
P3) 
[mm] 
Precise levelling 
-3.2 
-8.1 
0.7 
TLS 
-2.8 
-8.9 
0.7 
A (TLS-levelling) 
0.4 
-0.8 
0.0 
Table 3. Mean residuals (vertical displacements) of 
deformation analysis for different load situations 
detected by precise levelling as well as TLS. 
5. DISCUSSION 
The results by TLS present relative deformations as deflections 
of the cantilever slabs (outer side) of up to 20 mm under a 
maximal load of about 100 tons. This deflection range could 
only be detected by the area-wide analysis whereas the target 
spheres performed relative deformations of up to 6 mm due to 
the more central target setup in relation to the bridge girder. For 
the detection of absolute deformations of the bridge girder, the 
transformations of the TLS data into the reference height 
system defined by precise levelling were required. 
By comparing the transformed vertical displacements detected 
by TLS and the vertical displacements by precise levelling, the 
deformations of the bridge girder are within the same range. 
Maximum differences between the two measurement methods 
are around 3.5 mm. But considering the mean residuals for the 
different loading situations, the differences between TLS and 
precise levelling are less than 1.0 mm. 
Generally, the Felsenau viaduct mainly performed deformations 
as settlement and tilting. The deflection of the cantilever slabs 
were minor compared to the other deformations. 
6. CONCLUSIONS 
TLS is a very fast acquisition method and does not require 
deployment of any targets on the object. Since the 
measurements are carried out touchlessly the performance and 
accuracy of the measurements depend on the surface properties 
of the object. For scanning road surfaces, black asphalt and 
small angles of incident influence the data quality. As for the 
Felsenau viaduct, the carriageway could be detected up to a 
range of about 20 m from the scanner station. 
Regarding deformation monitoring on the Felsenau viaduct, 
TLS could replace the area-wide precise levelling. But, the 
transformation of TLS data into an absolute height reference 
system is essential for the detection of settlements and tilting of 
the bridge girder. Hence, for the connection to a height transfer 
reference outside of the viaduct precise levelling can not be 
omitted. 
Our load tests on the Felsenau viaduct have shown the 
feasibility of deformation monitoring by TLS. A comparison 
with precise levelling allowed assessing the measurement 
accuracy and quality of TLS. In general, TLS is suitable for 
detecting deformations within the mm-range. But concerning 
applications at accuracy level such as the load tests on Felsenau 
viaduct, other measurement methods like precise levelling are 
indispensable. Therefore, TLS well complements traditional 
geodetic measurement methods but cannot replace them 
completely. 
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mm