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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
  
  
  
  
  
Figure 1 — Location and shape of the landslide 
The landslide moreover is still active and consolidation works 
(creating drainages, removing debris, etc) have been realized 
during the last period; it must be stressed that this fact can in 
part invalidate the usefulness of the presented study in terms of 
comparison with the past, but the experimentation is in any case 
a test for the methodology and its results will be useful for 
monitoring this landslide in the future. 
A set of recent large-scale aerial photographs is available for 
this area, taken in year 2000, and two terrestrial Laser scanning 
surveys were realised in different periods in order to detect 
displacements of the study area: the first one in May 2001 and 
the second one in April 2004. 
The purpose of the work is to evaluate such methodologies for 
landslide monitoring applying them to a real case, evidencing 
the survey strategies, the procedure of elaboration of the laser 
data (filtering, merging, outliers detection ...), the techniques of 
recording the point clouds in a unique reference system, etc. In 
the following sections the surveys realised are shown, together 
with the methodologies adopted for data processing and the 
results of preliminary comparisons. 
2. THE PHOTOGRAMMETRIC SURVEY 
In April, 2000 a large scale aerial photogrammetric survey of 
the landslide was realised. Three photos of the area were 
collected at a mean scale of 1:4400 and oriented thanks to a 
GPS network of 24 ground control points (GCPs). Residual of 
bundle block adjustment on GCPs and tie points for outer 
orientation were on the order of few centimetres (Mora et al., 
2003). 
In order to have reference data of controlled quality, a Digital 
Terrain Model with a grid size of 2 m was generated using an 
analytical plotter (Galileo Siscam Digicart 40) and semi- 
automatic or manual plotting, with a significant amount of work 
by an expert operator. Figure 2 shows the orthophoto depicted 
on the DTM derived from this photogrammetric survey. 
It is clear that digital photogrammetric techniques are currently 
the most interesting solution for the automatic generation of 
terrain models and orthophotos, which are highly important for 
the study of a landslide phenomenon. 
  
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Figure 2. Three-dimensional perspective view of slope under 
study, coming from the 2000 photogrammetric survey. 
In addition to the photogrammetric process performed by 
analytical stereoplotter, the images were used to generate a 
DTM with a high-level digital photogrammetric workstation 
(Helava System) and the low-cost StereoView system (Menci 
Software), adopting semi-automatic and automatic procedures. 
The films were scanned using a RasterMaster (Wehrli & 
Associates Inc., NY, USA) photogrammetric scanner with 1000 
dpi resolution, sufficient to guarantee an high level of detail 
(ground pixel size about 12 cm). 
The DTM produced by Helava system was firstly generated 
automatically, with post-editing by the operator in order to 
correct errors deriving from the correlation procedure; editing 
consisted mainly of manual insertion of breaklines into 
incorrect zones, with consequent local recalculation of the 
surface area. It was afterwards compared to the one generated 
by the analytical plotter; the differences between the two 
models are characterized by a mean value of —15 cm, with a 
standard deviation of 42 cm, with the largest differences 
localized mainly in zones with complex morphology and 
shadowed areas. 
The result is therefore acceptable, indicating that digital 
photogrammetric techniques may now be adopted for routine 
elaborations, providing the products subjected to precise 
validation by an expert operator. 
3. THE MULTITEMPORAL TERRESTRIAL LASER 
SCANNING SURVEYS 
Terrestrial Laser Scanning, usually adopted in industry, piping, 
architecture, archaeology, control of quarries, has been applied 
in this work for deformation monitoring of the Cà di Malta 
landslide. 
Such a methodology offers the advantages typical of non- 
contact techniques, and moreover permits to collect in short 
time dense 3D point clouds over the surface of interest, to 
record a perspective image (intensity data and sometimes RGB 
data), it doesn't requires necessarily deployment of reflectors, 
and it permits immediately and easily to take measurements 
between points. 
There are various. terrestrial laser scanners available, 
characterised by different accuracy, measurement range and 
data acquisition quickness. The distance is measured applying 
different principles: the time-of-flight principle (ranging 
scanners) the phase difference, the triangulation. Ranging