28
Geotechnical News • March 2012
GEOTECHNICAL INSTRUMENTATION NEWS
Remote monitoring of deformation using Terrestrial
SAR Interferometry (TInSAR, GBInSAR)
Paolo Mazzanti
[Please refer to Mazzanti, GIN June
2011, pp 25-28 for more details.
Ed.]
Principal of operation
Terrestrial Synthetic Aperture Radar
Interferometry (TInSAR, also referred
to as ground based SAR interferome-
try, GBInSAR) is a RADAR technique
for the remote monitoring of displace-
ments. By the movement of a RADAR
sensor along a linear scanner (i.e. a
rail that allows precise micrometric
movements of the sensor), 2D SAR
images are derived. By comparing the
phase difference, i.e. interferometric
technique, of each pixel between two
or more SAR images acquired at dif-
ferent times, the displacements along
the instrument line of sight (LOS) are
derived. Thus, 2D color images of
LOS displacement can be achieved as
well as the displacement time series of
each pixel (Figure 1). TInSAR moni-
toring can be performed by installing
the equipment at a stable location
in a panoramic position, and it does
not require the installation of contact
sensors or reflectors in the monitored
area.
Main fields of application
The best application of TInSAR is the
continuous monitoring of unstable
slopes and dams. Other applications
include linear infrastructures such
as bridges, localized subsidence and
buildings. TInSAR monitoring of
buildings is quite challenging because
although it is possible to collect
highly accurate displacement data by
a non-contacting technique, it is quite
complex to detect vertical movements.
Accuracy and pixel
resolution
The theoretical accuracy of TInSAR
equipments is on the order of +/- 0.1
mm. However, both the precision and
the accuracy are strongly reduced by
the atmospheric noise. The precision
ranges from few tenths of mm to a few
mm, depending on the monitoring dis-
tance and the atmospheric conditions.
The pixel resolution of a terrestrial
SAR image ranges from few decime-
tres to several meters (depending on
the equipment and on the monitoring
distance). At a distance of 1 km, the
most common commercial equipment
has a resolution of about 0.5 x 4 m.
Main advantages
The main advantage of TInSAR
is probably the ability to monitor
displacements from a remote position
without the installation of targets or
sensors on the monitored ground or
structure. Other advantages include
applicability under any lighting and
weather conditions, including rain-
falls, clouds and fog; high data sam-
pling rate (few minutes); long range
efficacy (some km); high accuracy and
spatial control.
Main limitations
The main limitation is the complex
management, processing and inter-
pretation of TInSAR data. Other
limitations include: i) the size of
commercial equipment (up to 3 metres
long); ii) limited cone of view (some
tenths of degrees in both the H and V
planes); iii) unidirectional measure of
displacement (along the instrument
LOS) and iv) signal phase ambiguity
(i.e displacement higher than 4.5 mm
between two consequent images are
not easily detectable).
Future challenges
• The increasing number of applica-
tions will contribute to improve
both the technique and monitoring
good practice.
• Cheaper and smaller hardware
may improve the use of TInSAR,
especially in urban areas.
• Advanced algorithms and software
for the processing of data may
improve the usability and effec-
tiveness of TInSAR.
Commercial sources in North
America
In the author’s knowledge the fol-
lowing two companies are providing
services with TInSAR: Olson Engi-
neering Inc., Colorado (USA), http://
olsonengineering.com.and C-Core,
Kanata, Ontario (Canada),
-
core.ca. European companies with
longer expertise are listed in the article
referred to above.
Paolo Mazzanti
NHAZCA S.r.l. - spin-off “Sapienza”
Università di Roma,
Via Cori snc, 00177, Rome, Italy,
T: +39-3469776508,
E:
Figure 1. TInSAR displacement map
overlaid on the slope picture and
time series of displacement.
