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Geotechnical News June 2011
GEOTECHNICAL INSTRUMENTATION NEWS
TInSAR is a completely remote moni-
toring technique. This is an important
feature when faced with heritage situ-
ations and unsafe areas such as land-
slides.
On the other hand TInSAR can only
measure line-of-sight displacements
while RTS can be used for measuring
the 3D displacement field.
The accuracy of displacement mon-
itoring of the two techniques is difficult
to compare, since it strongly depends
on processing solutions and specific
site conditions. However, experiments
under ideal conditions have demon-
strated that similar accuracies can be
achieved.
Successful Applications and
Lessons Learned
In recent years successful applications
of TInSAR have demonstrated that
such a technique is a very powerful and
versatile solution for the monitoring
of different types of geotechnical
and structural engineering problems,
and especially for the continuous
monitoring in emergency conditions,
e.g. landslides and volcano flanks.
The recent application at an unstable
slope overlooking an artificial lake in
a mountainous region (up to 3000 m
above sea level), frequently affected by
fog, demonstrated the effectiveness of
TInSAR under any weather conditions:
a basic requirement for 24/7 emergency
monitoring.
But in the author’s experience, the
most complex application of TInSAR
has been the monitoring of a slope af-
fected by construction of a tunnel. Be-
cause of the presence of a large and
deep active landslide in rock material,
continuous monitoring of the slope
stability was required. Displacement
monitoring by conventional on-site
techniques (e.g. inclinometers, total
stations, GPS) was difficult due to the
geomorphology of the area and the on-
going construction work at the tunnel
entrance (gabions, anchored bulkheads
etc). Furthermore, a technique with
minimum intervention of personnel on
the slope for installing instruments or
targets was necessary for 24/7 emer-
gency monitoring. The continuous
monitoring of this slope by TInSAR,
from a distance of about 1 km, allowed
monitoring of every type of displace-
ment that affected the slope: excavated
debris, gabions, bulkheads etc. This al-
lowed engineering decisions to be made
efficiently, such as stopping tunnel ex-
cavation as a consequence of sudden
increases of slope displacement such as
an increase of one order of magnitude
of the velocity in a few hours. 3½ years
of continuous monitoring by TInSAR,
continuing to this date, demonstrated
the long-term reliability of this tech-
nique and its effectiveness in monitor-
ing both rapid and slow movements.
This feature, together with the capabili-
ty of monitoring without any targets on
the slope, makes TInSAR particularly
suitable for the monitoring of ground
movements that are characterized by
a high and non-homogeneous velocity
field and little vegetation cover. In ad-
dition to the project just described, sev-
eral cases of ground movement have
been monitored by TInSAR in recent
years, both for emergency and investi-
gation purposes.
Further suitable applications of TIn-
SAR for geotechnical problems are the
monitoring of dams and mines.
But the new frontier of TInSAR is
probably monitoring for investigation
purposes. For example, displacement
monitoring of several points over large
areas by TInSAR has recently been
proven for susceptibility analyses of
cliffs. In this application TInSAR has
been used for determining and map-
ping the most susceptible sectors of
cliffs, slopes and man-made structures.
The monitoring of buildings and
heritage situations in urban areas is a
new challenge for TInSAR. On one
hand there is the great advantage of
having highly accurate displacement
images by a non-contacting technique,
but on the other hand there must be
separate monitoring for vertical move-
ments. At present, combining with con-
ventional techniques is considered a
basic requirement in such applications.
Conclusion and Outlook
Terrestrial SAR Interferometry is an
emerging technique for geotechnical
monitoring.
Although
not
yet
extensively used in common practice,
TInSAR has been successfully proven
for monitoring some geotechnical
problems such as landslides and dams,
and is a promising method for some
others, such as cliffs and buildings.
The high price of equipment and
the complexity of data processing
and interpretation of results can
be considered the main limitations
for extensive use of this technique.
However, TInSAR can be more
efficient than conventional monitoring,
and in some cases also less expensive
if rational monitoring plans are made.
Private companies specializing on
TInSAR already exist. Furthermore,
the combination of TInSAR with other
techniques such as Terrestrial Laser
Scanner and robotic total stations may
further strengthen its effectiveness and
simplify the interpretation of results—
see an example in Figure 3.
References
Luzi, G. 2010. Ground based SAR
interferometry: a novel tool for
Geoscience. Geoscience and Re-
mote Sensing New Achievements,
508pp.
Bozzano, F., Mazzanti, P., Prestininzi,
A., Scarascia Mugnozza, G. 2010.
Research and development of ad-
vanced technologies for landslide
hazard analysis in Italy. Landslides.
Massonet, D., Fiegl, K. L. 1998. Radar
Interferometry and its application
to changes in the earth’s surface.
Reviews of Geophysics, 36(4),
441-500.
Paolo Mazzanti, Chief Executive
Officer, NHAZCA S.r.l. - spin-off
“Sapienza” Università di Roma,
Via Cori snc, 00177, Rome, Italy,
Phone: +393469776508, email: paolo.
