International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
The study site (Figure 1) is located on the slope of the
Brustolè mount, in front of the small town of Arsiero
(Vicenza, northern Italy). This site is actually undergoing a
strong debate among the inhabitants and local government
authorities about the exploitation of the area as a huge quarry
to produce building material. The dispute originates from the
uncertainty about the instability of the underlying mountain
slope, which was interested in 1966 by a landslide. After this
event, the area has been continuously monitored by
measuring the dynamics of terrain displacements. The
landslide covers approximately a surface of 600000 m°, with
an extent of around 400 m in vertical direction and 1 km in
the horizontal direction, at the bottom of the slope. Elevation
ranges from 350 to 750 m a.s.l. The main sliding surface is
located at a depth of 20 m at the top and at the bottom of the
landslide body, while it reaches a depth of 100 m in its
central part. The volume of material involved in the event of
1966 was estimated to be around 20-30 millions of cubic
meters (Bitelli et al., 2009).
Figure 2: View of the bottom side of the landslide.
In order to perform a 3D simulation of the morphological
changes the site may undergo during the excavation of the
quarry, on February 2011 the entire area was surveyed with a
long-range TLS, the Riegl LMS-Z620. After a few weeks,
still during the vegetation dormant period, a second survey
was carried out with a full-waveform system, the Riegl VZ-
400. Due to time constraints and the limited operational range
512
of this laser scanner (max. 600 m), only the lower part of the
landlside body could be surveyed, where coppice and high
forest alternates with rocks and cliffs. The presence of dense
vegetation, ranging from low understore to high trees, added
complexity to the scan of the area as it covered multiple strata
above the ground (Figure 2). Tables 1 and 2 show the main
technical features of the LMS-Z620 and of the VZ-400 laser
scanners, respectively, while table 3 reports some properties
of the scans acquired with both instruments.
Table 1: Technical specifications of the Riegl LMS —Z620
Field of View 360? (H) x 80? (V)
for natural targets, p > 10% up to 650 m
for natural targets, p > 80 % up to 2000 m
0.15 mrad
up to 11000 pts/sec @ low scanning rate
(oscillating mirror)
upto 8000 pts/sec (à) high scanning rate
(rotating mirror)
near infrared
Max. Measurement range
Beam divergence
Measurement rate
Laser wavelength
Accuracy 10 mm
Repeatabilit 10 mm (single shot), 5 mm (averaged)
P y g
Table 2: Technical specifications of the Riegl VZ-400
Field of View
Max. Measurement range
(Long range mode)
Beam divergence
360? (H) x 100? (V)
for natural targets, p 2 20 % up to 280 m
for natural targets, p > 80 % up to 600 m
0.3 mrad
42000 meas/sec (Long range mode
Measurement rate 122000 e (High me UE
Max. number of targets
per pulse
Laser wavelength
Practically unlimited
near infrared
Accuracy 5 mm
Repeatability 3 mm
Table 3: Some properties of acquired laser scans
LMS-Z620 VZ-400
# of scans 7 3
Average meas. 3400000 15300000
per scan
Max. range 900 m 350 m
Average scan 0.5 mrad 0.5 mrad
resolution (225 cm @ 500 m)
3. SCAN REGISTRATION AND GEOREFERENCING
All acquired scans were georeferenced in the same reference
frame (WGS-84) using the so called “backsighting orienta-
tion” procedure. Firstly each laser sensor was optically
centered over a point, whose coordinate were known by GPS
static measurements, and levelled through the built-in dual
axis compensator. Then the remaining degree-of-freedom
(rotation about the vertical axis, Z) was fixed by orienting the
instrument reference system (IRS) toward a known point.
This last task was accomplished by scanning a retroreflective
backsighting target, whose position was surveyed with static
GPS, as well. Next, this approximate registration was
