The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
- when the model of the monitored area has been generated, 
computations about volume variations as well as on the 
differences between the multitemporal models of the same 
object can be carried out. Since the model accuracy (in the 
case of environmental applications) is usually centimetric, 
only displacements greater than a few centimetres can be 
detected; 
- laser scanners are usually lighter and less bulky than GB-SAR 
instrumentation and it is possible to transport them without 
particular vehicles; 
- laser scanner techniques allow dense digital elevation models 
(DDEMs) of the observed object to be generated; in the case 
of multitemporal scans, it is possible to detect displacements 
in each small portion of the observed area and not in pixels of 
a few square metres of dimension as in GB-InSAR products; 
- no problems occur in the case of a change in the laser scanner 
position between repeated measurement campaigns because 
the reference system of the models is “fixed” on the markers, 
while even millimetric changes in the position of GB-SAR 
instrumentation can dramatically reduce the measurement 
accuracy; 
- the measurement range can vary to a great extent for different 
instruments; in general it can vary between 10 m up to some 
kilometres; 
- thanks to the comparison between multitemporal scans, 3D 
displacements can be detected, while with GB-SAR only the 
displacement component parallel to the line of sight of the 
instrument can be detected. 
4. CONCLUSIONS AND FUTURE WORK 
In this work, both GB-InSAR and TLS measurements were used 
to monitor the landslide of the Ex-Locatelli quarry. 
No displacements occurred during the five days of monitoring: 
the landslide is in fact quiescent but at risk of reactivation, and 
no precipitations occurred during the monitoring campaign. The 
local Authorities are at present considering a new campaign. 
Thanks to this work, both techniques have been applied and 
their principal features have been compared. 
The GB-InSAR technique can be useful for many applications, 
such as continuous or repeated monitoring of slopes, landslides, 
quarries, glaciers and of the snow cover (Achache et al., 1996; 
Ferro-Famil et al, 2005; Fortuny-Guasch et al, 2005) . It can 
also be applied to monitor buildings and large infrastructures, 
such as dams, bridges and towers, either in static or dynamic 
conditions. This technique can be very useful for the remote 
monitoring of terrain slopes and as an early-warning system to 
assess the risk of rapid landslides. 
Its measurement accuracy has been estimated from a statistical 
point of view both in a test-site in Florence and during the 
monitoring campaign of the Baveno landslide. In the case of 
continuous monitoring, a sub-millimetric accuracy can be 
reached (± 0.70 mm at 95 % reliability in the case of study), 
while in the case of repeated monitoring it is not possible to 
reach a similar accuracy because of phase decorrelation. In this 
latter case, it is necessary to turn to different techniques, such as 
the “coherent points" technique, with a decrease in accuracy; in 
this case, the displacement measurements are limited to many 
sparse points and the broad information provided by 
interferometric displacement maps obtained with continuous 
monitoring is thus lost. 
The TLS technique allows a complete and accurate DEM of the 
monitored area to be obtained. It can be useful for natural 
hazard and risk assessment where morphological investigation 
is a starting point to evaluate stability properties. In the case of 
multitemporal scans, it is possible to compute volume variations 
of the observed object, providing 3D displacement 
measurements, while, with the GB-InSAR technique, only the 
displacement component parallel to the line of sight of the 
instrument can be detected. 
These two techniques can be considered complementary. TLS 
can be usefully used to generate an accurate digital model on 
which SAR images can be focused. The data obtained by SAR 
could also be linked to the TLS measurements, but limited to 
some points in order to reconstruct the absolute phase 
information of the entire area observed by the radar. 
It can be concluded that the integration of GB-InSAR and TLS 
techniques is a powerful remote sensing system for 
environment monitoring. 
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Acknowledgements 
The authors wish to acknowledge the Department of Electronics 
and Telecommunications at the University of Florence for the 
GB-InSAR measurements and processing and the Verbano 
Cusio Ossola Province Authorities for their assistance in the 
logistics of the measurement campaign.