The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
2.2 TLS measurements 
Terrestrial laser scanner measurements were perforrmed during 
the GB-InSAR monitoring to obtain a precise and updated 
DEM of the landslide. 
A Riegl LMS-Z420 laser scanner, which allows long range 
measurements (up to 700 m) and centimetric precision in the 
2.5 cm range, was employed (Fig. 8). 
The laser scanner was installed a few metres from the GB-SAR 
thus ensuring good visibility of the landslide and of the markers 
installed in the surrounding area. These markers are necessary 
to georeference the acquired data and their position was 
acquired through topographic measurements (see section 2.3). 
The laser scanner data acquisition lasted about 40 minutes for 
each of the two scans necessary to describe the landslide and 
about 33 million points were acquired. 
The global point cloud used to generate the 3D model of the 
landslide was obtained after filtering and registration of the two 
scans. 
Figure 8. The Riegl LMS-Z420 Laser scanner 
The laser scanner data were processed with a new Sirlo 
software realized thanks to a collaboration between the SIR 
society (Italy) and the Geomatics Research Group of the 
Politecnico di Torino. 
The laser scanner was firmly connected to a calibrated digital 
camera (the Nikon D1X camera). Many digital images of the 
scenario were acquired and they were employed to integrate the 
laser scanner data with their radiometric content. 
Thanks to the Sirlo software it was also possible to generate 
solid images of the landslide (Bomaz et al., 2003), which allow 
direct measurements to be easily made on the point cloud, such 
as distances, angles, plane orientations,.. 
A portion of the processed laser scanner data is reported in 
Figure 9. 
Figure 9. Portion of the processed laser scanner data 
2.3 Topographic measurements 
In order to correctly locate the radar and laser scanner data it 
was necessary to create a local coordinate system made up of 
three control points and many markers. The coordinates of the 
control points were estimated using relative-static GPS 
positioning, while the coordinates of the other points were 
acquired by the total station. This latter instrument was also 
employed to measure the positions assumed by the active radar 
calibrator that are necessary for the radar data georeferencing. 
All the topographic measurements were adjusted with a 
commercial software, and centimetric accuracy was obtained in 
the estimation of the coordinates of the measured points. 
2.4 Results of the campaign 
The final SAR interferometry product consists of displacement 
maps of the scenario, which provide information about the 
distribution and entity of the movements. 
The interferometric maps were obtained through a masking 
procedure that excludes areas with lower coherence than the 
reference lower limit value (0.9 in this case) and by focusing the 
radar images on a DEM of the scenario. 
Three displacement maps - corresponding to the three 
sequences of acquired radar images - were obtained. One of 
them is reported in Figure 10. 
Figure 10. Displacement map relative to the first sequence of 
SAR images 
No appreciable displacements are present in any of the maps as 
could be foreseen; the landslide is in fact quiescent but at risk of 
reactivation and no precipitations occurred during the 
monitoring campaign. 
It will be possible to repeat the SAR measurement campaign 
four-six months after the first campaign in order to determine 
any displacements that have occurred during the time interval 
between the two campaigns. In this case, it will be necessary to 
adopt the “permanent scatterers” (or “coherent points”) 
technique (Ferretti et al., 2001). 
This technique is based on the selection of stable coherent radar 
image pixels - between successive campaigns - whose 
interferometric phases can be considered only affected by 
atmospheric variability and any spatial movements. 
The final products of laser scanner measurements are 3D 
models and solid images of the scenario. In this case, we 
obtained a complete 3D model and four solid images of the 
landslide. Only on the upper part of the scenario laser data was 
the density not so good because of the long distances, which 
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