MEASUREMENT OF DAM DEFORMATIONS BY TERRESTRIAL
INTERFEROMETRIC TECHNIQUES
Mario Albaa, Giulia Bernardinib, Alberto Giussania, Pier Paolo Riccib, Fabio Roncoronia, Marco Scaionia
Paolo Valgoic, Katherine Zhangd
a
Politecnico di Milano, DIIAR, Polo Regionale di Lecco, via M. d’Oggiono 18/a, 23900 Lecco, Italy
{mario.alba, alberto.giussani, fabio.roncoroni, marco.scaioni}@polimi.it
b
IDS Ingegneria dei Sistemi S.p.A., via Livornese 1019, 56122 Pisa, Italy, www.ids-spa.it
{g.bernardini, p.ricci}@ids-spa.it
c
A2A, ATO/SIE, Grosio (SO), Italy, paolo.valgoi@aem.it
d
Beijing PT Equipment Co. ltd, 50 Xi San Huan Bei Road, 100044 Beijing, China
Commission I, WG I/2
KEY WORDS: Interferometric SAR, Deformation Analysis, Dam Monitoring, Engineering Surveying, Ground-Based InSAR
ABSTRACT:
In this paper the application of a novel non-contact GBInSAR sensor to the measurement of daily deformations of an arch-gravity
dam is described. The sensor, named IBIS, is a Ku-band interferometric radar sensor apt to simultaneously monitor the displacement
response of several points belonging to a large structure. Moreover, the possibility of scanning the monitored object with the radar
sensor moving along a stable track enables to implement the interferometric SAR technique to improve the cross-range resolution in
the direction parallel to the baseline. The presented application addresses the monitoring of the displacement of the dam due to an
increasing load of the water basin during two days and to temperature change. The displacement results have been compared with
the measurements obtained by a coordinatometer installed on the central section of the dam for validation purpose; a good
agreement between innovative radar methods and well assessed monitoring sensors has been achieved.
1. INTRODUCTION 1.1 Terrestrial laser scanning
In the recent years the need of information about deformations Different authors reported about applications of Terrestrial
of large concrete dams has been highly demanded by Laser Scanning, which allows to capture dense point clouds
researchers and operators involved in maintenance and safety of made up of 3-D unspecific points with a high degree of
these structures. Indeed, nowadays the development of automation, but with a poor accuracy for deformation
innovative techniques for the static and dynamic structural measurement. This result could be improved by exploiting the
modelling would allow to sharply improve the capability of data redundancy when the surveyed object features a regular
predicting collapses, reducing so that the risk of disasters. A geometry (see e.g. the application to tunnel deformation
fundamental prerequisite that all mathematical models should measurements - Van Gosliga et al., 2006 – or to a television
have to adhere to reality is the availability of precise and dense tower - Schneider, 2006), or when it can be decomposed in
observations, either from a geometric point of view and about many small planar patches (Lindembergh & Pfeifer, 2005). In
boundary conditions. Several monitoring techniques could give both cases, equations of regular surfaces can be estimated based
their contribute to this aim, accounting for geodetic on a redundant dataset of observed points, and accuracy higher
measurements and for sensors capable of measuring local than that of the original 3-D observations can be achieved (see
deformations, rotations, and displacements. Monserrat & Crosetto, 2008). Unfortunately, errors due to
sensor georeferencing at different epochs usually worsen the
Broadly speaking, current techniques allow one to monitor a set quality of results (Alba et al., 2006). By considering results
of specific control points on a dam, without covering every achieved so far, TLS can be used to evaluate seasonal
portion of the structure itself. This lack of information is an deformations of structures with points featuring a few cm
important drawback for structural modelling, especially when displacements, but not for the continous monitoring.
comparing previsions of theoretical analysis with true
deformations under external conditions is needed. 1.2 Ground-Based interferometric SAR
In order to provide deformation measurement on large portions In the last decade some terrestrial sensors have been developed
of a structure’s surface, experimentation of two different kinds to perform Ground-Based Interferometric SAR (GBInSAR)
of sensors have been carried out in the latest years: Terrestrial measurement of deformations (Rudolf et al., 1999; Harries et
Laser Scanning (TLS) and Ground-Based Interferometric SAR al., 2006; Bernardini et al., 2007c). Even though the density of
(GBInSAR). tracked points is lower w.r.t. TLS, the intrinsic achievable
accuracy enables its use for continuous monitoring of large
structures as well. Nevertheless, in case of constructions like
dams, featuring large regular surfaces, a huge point density is
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not a key issue, like the accuracy is. The Surveying Dept. of Politecnico di Milano gave to IDS the
opportunity to perform a real-scale test with IBIS-L system on
GBInSAR systems are capable to make measurement of an arch gravity dam in Alta Valtellina, and to compare the radar
deformation along the Line-of-Sight (LoS) from the sensor head measurements with those obtained by a coordinatometer. The
to the surface to be monitored. Thus only variations in range dam was loaded by the water of the basin whose level was
can be evaluated, which however could be decomposed along increasing during the two days survey. On the same dam an
other lines if the local geometry is known (see Sub-sec. 3.3). experimental application on the use of TLS for deformation
The spatial resolution of measurements is defined in both range measurement is ongoing since 2005 (Alba et al., 2006). In
and cross-range directions. The target surface is divided in addition, the availability of a 3-D model of the whole
pixels, as can be seen in figure 3, and the pixel is tracked along construction has resulted in the knowledge of local geometry,
different epochs. The surface geometry and position plays a which is almost important to augment the information
fundamental role in the localization of measured points. On the achievable from radar measurements. Currently IBIS is an
other hand, also TLS can be used to detect deformations operational commercial system that has been conceived to be
occurring in range directions, because in the other it cannot used. Results of these tests are summarised in section 4.
operate if there are not discontinuities (like e.g. on a concrete
dam face). An advantage of TLS is the better point localization, Hereinafter the paper continues with the description of IBIS-L
thank to the recording of horizontal and vertical angles as well. radar sensor (Sec. 3) and with the presentation of the radar
In literature an experience of deformation monitoring using a techniques and principles adopted (Sec. 4).
GBInSAR sensor is reported by Tarchi et al. (1999). A large
double curvature dam was observed at 5 epochs during a period
of about 2 months. The radar system was periodically 2. IBIS-L DESCRIPTION
repositioned in the same position, and the data reconstruction
into the same reference system was supported by the The IBIS-L microwave interferometer (Fig. 1) is a Ku-band
availability of a DSM of the dam itself. Deformations of the (16.6-16.9 GHz) radar sensor designed for the simultaneous
whole downstream face has been measured and validated in monitoring of the response of several points belonging to a
comparison to readings of a coordinatometer internal to the dam. large structure, providing for each point the displacement
Even though this check concerned only a few points in the main between two different epochs.
vertical section, it resulted in an accuracy under ±1 mm.
With respect to conventional contact sensors, like strain-gauges,
Recently a novel radar system, named IBIS, was developed: the use of a non-contact radar-based techniques overcomes
this system is able to measure the dynamic and the static some limitations and drawbacks. First of all, the number of
response of many points of a structure with up to 10÷20 μm control points is strongly increased, so that IBIS-L supplies a
displacement sensitivity (Bernardini et al., 2007a). The sensor continuous displacement map of the entire observed area which
was studied and setup by IDS company in collaboration with can reach up to hundreds of thousands of square metres. The
the Dept. of Electronics and Telecommunication of the Florence radar system simultaneously measures the displacements of all
University (Pieraccini et al., 2004, 2005). points in the area illuminated by the antenna beam with
accuracy up to 0.1 mm. On the opposite, the precise localization
Currently IBIS is a commercial GBInSAR system that has been of control points is more difficult. The access to the structure is
conceived to be used independently by end-users, without not needed, because remote structural monitoring can be
specific knowledge of radar theory. It is based on two performed without installing sensors or optical targets on the
equipment configurations aimed to different applications: surface to measure.
• IBIS-S: it’s a 1-D radar sensor that can be used for IBIS-L provides also detailed information on the movement of
static and dynamic response measurement; it features specific points belonging to the scenario, because for each
high range resolution and short range from sensor to control point the position along range is archived in a DB. The
target (up to 1,000 m); sampling rate might be up to an interval of 5 minutes. This
• IBIS-L: it’s a GBInSAR sensor based on the IBIS-S capability allows the continous deformation monitoring of
radar; it is devoted to static response measurement and structures with fast displacements. In addition, the IBIS-L
features both range and angle (cross-range) resolution, system can be accurately repositioned at different epochs, in
and medium range (up to 4,000 m). case a periodic control in a long-period is needed. In this case,
an uncertainty limited to about ±0.2 mm is to added up to the
Both configurations exploit Interferometric technique, derived deformation measurements.
by satellite earth monitoring application, in order to detect sub-
lambda displacement of the structure induced by environmental Microwave interferometer can be used both day and night and
or human stresses. in all weather conditions.
The assessment of the IBIS in the -S configuration was Furthermore, the possibility of operating even at a significant
performed by IDS and the Dept. of Structural Eng. of distance and without the need of installing and wiring sensors
Politecnico di Milano, within an ongoing research programme permits the investigation during emergency situations when
aimed to the validation of IBIS-S performance in dynamic monitoring activity can be required to ensure the safety of
testing of full-scale structures. The radar system was used in people.
ambient vibration testing (AVT) of several different R.C.
bridges. Results of these tests are available in Bernardini et al. The main operational characteristics of IBIS-L system are
(2007b). summarized in table 2.
As figure 1 shows, the IBIS-L system consists of the following
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modules: exploiting the duality between time and frequency domains:
instead of transmitting a short pulse of duration τ in time with a
1. the radar module: this unit generates, transmits and large bandwidth in the frequency domain as pulse radars do,
receives the electromagnetic signals which will be IBIS-L radar module transmits a burst of N monochromatic
processed in order to measure the displacement of the pulses equally and incrementally spaced in frequency (with
investigated structure; fixed frequency step of Δf) within a bandwidth B:
2. the linear scanner consisting of a 2.5 metre long
aluminium track, along which the sensor is moved B = ( N − 1) Δf (1)
under the control of a step-by-step motor;
3. the control PC, installed with the system management
software. It is used to configure the acquisition For a pulse radar, the range resolution Δr is related to the pulse
parameters, to manage and to store measurements and duration τ by the following elementary relation Δr=cτ/2, where
to display first results just after ground data acquisition; c is the speed of light in free space. Since the pulse duration is
4. the power supply unit, providing power to the system equal to the reciprocal of the frequency bandwidth B of the
through a pack of two 12V batteries or connection to a pulse (τ=1/B), the range resolution may be expressed as:
external energy supplier (electricity main network or
photovoltaic panels). c
Δr = (2)
2B
Eq. (2) highlights that the range resolution of the system is
inversely proportional to the swept bandwidth of the E.M. wave
transmitted by the radar.
By taking the Inverse Discrete Fourier Transform (IDFT) of the
samples acquired in the frequency domain, the response is
reconstructed in the time domain of the radar. The amplitude
range profile of the radar echoes is then obtained by calculating
the amplitude of each sample of the IDFT of the acquired vector
samples. This range profile gives a one dimensional map of
scattering objects in the viewable space in function of their
Fig. 1. IBIS-L system installed on a concrete foundation relative distance from the equipment.
The concept of range profile is better illustrated in figure 3,
Parameter Value showing an ideal range profile obtained when the radar
Maximum operational distance 4,000 m transmitting beam illuminates a series of targets at different
Spatial resolution @ 1Km 0.5 x 4.5m distances and different angles from the sensor. As previously
Acquisition rate 5 min stated, the range profile refers to N target points, being 0.50 m
Displacement sensitivity (accuracy) 0.1 mm apart. This means that two or more different objects with
Power consumption 100 Watt similar scatter properties lying into the same range bin (in this
Weight of the whole system 130 kg case with a depth of 0.50 m) would result in a unique radar echo.
In this case, it is impossible to discriminate about displacements
of different points, but the echo will give the description of the
Table 2. IBIS-L operational characteristics mean changes of all scatterers.
3. PRINCIPLES OF THE ADOPTED RADAR
TECHNOLOGY
The IBIS-L sensor is based on three well-known radar
techniques: (i) the Stepped-Frequency Continuous Wave (SF-
CW), providing the system with range resolution capability; (ii)
the Synthetic Aperture Radar (SAR) technique that, combined
to the SF-CW technique, allows the system to retrieve a two-
dimensional image of the scenario, resolving it into several
pixels of limited area; (iii) the interferometric technique that
allows the system to measure at the same time the
displacements of the monitored area, thanks to the comparison
of the phase information of the backscattered electromagnetic
waves collected at different times. In the following these
techniques will be briefly reviewed.
3.1 SF-CW technique
The Stepped-Frequency Continuous Wave (SF-CW) technique Fig. 3. Range resolution concept
provides the system with range resolution capability, up to 0.5m
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3.2 SAR technique reflected by the object in different time instants.
The displacement of the investigated object is determined from
Synthetic Aperture Radar technique allows radars with wide the phase shift measured by the radar sensor at the discrete
physical antenna beam width to obtain high angular resolution acquisition times. The Line-of-Sight (LoS) displacement dLOS
in azimuth thanks to the acquisition of the scenario from (i.e. the displacement along the direction of wave propagation)
different view angles: the coherent composition of the and the phase shift Δϕ are related by the following:
acquisitions permits to obtain a synthetic antenna whose beam
width is inverse proportional to the relative movement between
the scenario and the radar (Ferretti et al., 2007). λ
For strip-map radar as IBIS-L the obtained angular resolution is dLoS ∝ − Δϕ (4)
given by: 4π
λ The first applications using the interferometric technique were
Δϑ = (3)
2L performed by satellite to detect the displacement of large areas
of terrain, with a resolution at ground level of a few meters;
now the same technique can be used with radars installed on the
where λ is the wavelength of the E.M. signal and L is the length ground, permitting the illumination of specific areas with a very
of the relative movement of the radar head w.r.t. the target. In high range resolution.
case of IBIS-L, the movement of the sensor module on the 2 m
linear scanner permits the system to have an angular resolution It is worth underlining that the interferometric technique
of 4.5 mrad. provides a measurement of the LoS displacement of all the
pixels of the structure illuminated by the antenna beam; once
The combination of the SF-CW technique with the SAR dLoS has been evaluated, the vertical and horizontal
technique leads to the radar image being organized into pixels displacements (or their projection on another tilted 3-D plane)
with dimensions of: 0.5 m in range and 4.5⋅10-3r m in cross- can be easily found by making some geometric considerations
range, where r is the distance from radar to target. (see the example reported in figure 5).
The following figure 4 shows an example of a resolution grid
IB IS -L
for a system with a distance resolution of 5 m and angular
resolution of 5.2 mrad. A look to this figure enable to quickly
understand that the shape of the object under monitoring is
fundamental to allow the discrimination between specific
observed points. Considering for instance the range and cross- h r
range directions in the horizontal plane, if the object features a α
vertical surface, the number of observed scatterers will be very M onitored A rea
small. On the contrary, if the object presents a tilted surface, the d LO S
d
number of scatter points would sharply increase.
100 Fig. 5. Line-of-Sight displacement vs projected displacement
80
4. APPLICATION TO A FULL SCALE DAM:
range (m)
60 pixel SUMMARY OF RESULTS
40 An arch-gravity dam was investigated by using IBIS-L system
to measure deformations due to the filling of the water basin as
20 well as to variation of the structure temperature. The Cancano
dam (Alta Valtellina, Italy) features about 90 m height from
0
bottom to top, and 350 m length on the crest, and it is managed
-60 -40 -20 0 20 40 60 by A2A company (see Fig. 6). The dam is currently controlled
cross-range (m)
by topographic techniques, that consist in two high precision
leveling lines on the top crest and on the middle height corridor
of the structure, in optical collimators to detect horizontal
Fig. 4: Example of a spatial resolution grid displacements, and in a column of coordinatometers positioned
in the middle vertical section. In addition, a precise DSM of the
3.3 Interferometric technique structure itself was achieved by TLS. The availability of all
these measurements allows to perform a GBInSAR data
Once the 2-D map of a structure has been determined at validation.
uniform sampling intervals, the displacement response of each
pixel is evaluated by using the Interferometic technique. Data acquisition by IBIS-L has been performed at a mean
Interferometry is a powerful technique that allows the distance of 400 m far from the dam mid-point, during a period
displacement of a scattering object to be evaluated by lasting 37 hours. The IBIS-L system has been setup on a
comparing the phase information of the electromagnetic waves
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temporary stand-points, because the replacement of the of points which are vertically widespread are shown. As you
instrument hasn’t been foreseen for this test. As shown in figure can see, the trend of the observed dam displacements agrees to
6, the radar system has been placed just in front of the dam’s the foreseen static behavior in both cases. Note the magnitude
downstream face. This positioning has allowed to capture the of maxima displacements along the observation period is under
entire dam displacement along in the range direction during the 2 mm. Some outliers are present in time-series corresponding to
whole observation time. The time needed to scan the whole points P34 and P30, which probably are placed on positions
downstream has been 9 minutes, and each scanning cycle has disturbed by local turbulence or they might be located on a
been repeated without intermediate breaks. It is relevant to surface featuring bad reflectivity, despite of the high coherence.
notice that the configuration of parameters needed to correctly On the other hand, these outliers does not result in trend errors,
perform the data acquisition is very easy, because this task can and can be removed by low-pass filtering in the time domain, or
be performed by also non-skilled operators. During the data by averaging displacements evaluated on close points in the
acquisition, the control software allows one to check the space domain. Indeed, by comparing displacements of points
focalisation map, which is an information of the reflectivity P30 and P29, whose position differ for only 15 m, it is possible
properties of the object illuminated by the SAR sensor. In to see that only the first of them is affected by anomalous noise
addition, a check on intermediate displacements of points (see Fig. 9).
tracked on the structure can be seen. This option is very
important for continuous monitoring applications.
Fig. 6 – IBIS-L positioned in front of the downstream face of
the Cancano dam (Alta Valtellina, Italy)
The results of GBInSAR measurements are 2-D deformation
maps of displacements, which reached a maximum value of
about 4 mm in the central section. Consider that, in years with
the biggest variation of water level in the basin, the full
displacement of this point might reach about 80 mm. In figure 7,
maps corresponding to three different epochs (after 10, 22 and
37 h) during the test at Cancano dam are shown.
According to an integer ambiguity of 4.5 mm (Δϕ= 1 rad). such
a displacement can be automatically tracked if IBIS-L is Fig. 7 – Complete displacement maps after 10, 22 and 37
continuosly acquiring data, and not more that 1 cycle is hours of observation
increased from an observation epoch and another (in this
application these are separated by a 9 minute rate). In case of
repositioning of IBIS-L, the processing tool is not able to detect
displacements larger than the integer ambiguity. A solution, to
this problem could be provided by integrating the GBInSAR P20
system to other ranging sensors featuring lower precision and P6 0 P32
measurement rate, but that would be able to reconstruct low 2
P1 P34
frequency displacements (e.g. TLS or robotic total stations). P30 P31
P29
By thresholding points on the basis of their coherence (ρ) and
their Signal-to-Noise Ratio (SNR), it is possible to select those
which are high accurate control points. The higher are the
selected thresholds, the higher is the accuracy in the
measurement of the displacement of the selected point. In
figure 8, a sub-set S0.99 of only points with ρ>0.99 is shown. For
each of these the time-series of displacements is fully available.
For 5 points on the dam crest, the displacements are shown in Fig. 8 – Location of tracked points on the dam downstream face
the upper part of figure 9, while in the lower part displacements with a coherence ρ>0.99
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Achievements of this experimentation are very promising and
open new perspectives for static analysis of large dam
behaviour, and of other kinds of large constructions as well.
Indeed, instruments and sensors which have been applied so far
for measuring dam deformations feature an high accuracy and
reliability, even though only a limited number of points could
be observed. On the other hand, during this experimentation a
very huge number of monitored points has been measured
(some thousands) during a period of 37 hours. Also in case of
the restricted sub-set S0.99 of only points featuring very high
coherence, this account for more than 30 points which are
widespread on the whole dam downstream face. In addition, no
artificial reflectors are needed. The global behaviour of
measured displacements and a quality check based on a
comparison to readings from a coordinatometer have enhanced
an accuracy of this GBInSAR system under ±1 mm. At the
current state of the art, this cannot be achieved by other
instruments, considering that mountain environments where
dams are usually located might requirethe sensor positioning
very far from the structure to be monitored (also some hundreds
meters); obviously, this fact is a strong drawbacks for remote
displacement sensors (e.g. for robotic total stations or automatic
Fig. 9 – Time-series of displacements of a sub-set of high- collimators), while IBIS-L can operate also from some
coherence points (ρ>0.99), according to Fig. 8. On the upper thouthands meters.
graphic, five points belonging to the dam top crest; on the lower,
three points that are vertically widespread Moreover, the temporal data acquisition rate (9 minutes) and
the degree of automation are excellent, if compared to other
4.1 Data validation monitoring sensors. These characteristics make possible to use
GBInSAR systems for continuos monitoring purpose, and to
At the same time of GBInSAR measurements, the dam was integrate them with other monitoring techniques
under monitoring by a coordinatometer, whose results were
compared to IBIS-L results and exhibited a good agreement, i.e. A second important achievement of this test concerns the
differences between measurements achieved by different possibility by the end-users to adopt a commercial system, like
instrumentations during 24 hours have been compared, resulting IBIS-L is, for the current practise of dam monitoring activities.
in discrepancies with a RMSE of ±0.2 mm (see Fig. 10). The presence of a simple GUI, the low number of parameters to
set up and the standardization of SAR processing, allow its use
also by non-skilled people in radar techniques.
However, the experimental and theoretical research in this field
needs further improvements. In particular, the precize
localization of control points is to be developed. Furthermore,
the integration between TLS and GBInSAR data is expected to
open to further interesting applications, where the former
system is able to detect lower frequency deformations with a
higher point density, while the latter is capable to monitor
higher frequency at a lower spatial resolution.
AKNOWLEDGEMENTS
Thanks go to A2A ATO-SIE (Grosio, Italy) for the availability
Fig. 10 – IBIS-L single pixel displacement (green circles) on
of the dam of Cancano Lake and for the cooperation during
the middle of the dam crest, compared to coordinatometer
experiments with the GBInSAR system.
measurements along the entire period of observation
REFERENCES
5. CONCLUSIONS
Alba, M., Fregonese, L., Prandi, F., Scaioni, M., and P. Valgoi,
The application of an innovative, radar-based measuring system
2006. Structural Monitoring of a Large Dam by Terrestrial
(IBIS-L by IDS, Italy) to static deformation of a large arch-
Laser Scanning. IAPRSSIS, Vol. 36/5, pp. 6, on CDROM.
gravity dam has been described in the paper together with the
system functioning principles.
Bernardini, G., De Pasquale, G., Bicci, A., Marra, M., Coppi, F.,
Ricci, P. and M. Pieraccini, 2007a. Microwave interferometer
The test results highlight very good performance of this sensor
for ambient vibration measurements on civil engineering
coupled with the SAR technique in the measurement of slow
structures: 1. Principles of the radar technique and laboratory
movements, if compared with standard monitoring instruments.
138
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B1. Beijing 2008
tests. In: Proc. of EVACES’07, Porto, Portugal, 24-26 Oct, on
CDROM.
Bernardini, G., De Pasquale, G., Gallina, N., and C. Gentile,
2007b. Microwave interferometer for ambient vibration
measurements on civil engineering structures: 2. Applications
to full scale bridges. In: Proc. of EVACES’07, Porto, Portugal,
24-26 Oct, on CDROM.
Bernardini, G., Ricci, P., and F. Coppi, 2007c. A ground based
microwave interferometer with imaging capabilities for remote
measurement of displacements. Presented at GALAHAD Work.
within the 7th Geomatic Week, Barcelona, Spain, 20-23 Feb.
Available online at www.idscompany.it/upload4 (last accessed
on 30th April 2008).
Ferretti, A., Monti Guarnieri, A., Prati, C., Rocca, F., Massonet,
D., 2007. InSAR Principles: Guidelines for SAR Interferometry
Processing and Interpretation. ESA Publications, Noordwijk,
The Nederlands.
Harris, N., Noon, D., and K. Rowley, 2006. Case Study of
Slope Stability Radar used in Open Cut Mines. In: Proc. of Int.
Symp. on Stability of Rock Slopes in Open Pit Mining and
Civil Eng., Cape Town, South Africa, 3-6 Apr, pp. 335-342.
Lindenbergh, R. and N. Pfeifer, 2005. A statistical deformation
analysis of two epochs of terrestrial laser data of a lock. Proc.
7th Optical 3-D Measurement Techniques, Vienna, Austria, 3-5
Oct, Part 2, pp. 61-70.
Monserrat, O. and M. Crosetto, 2008. Deformation
measurement using terrestrial laser scanning data and least
squares 3D surface matching. ISPRS JPRS, Vol. 63(1), pp. 142-
154.Pieraccini, M., Fratini, M., Parrini, F., Macaluso, G., and C.
Atzeni, 2004. Highspeed CW step-frequency coherent radar for
dynamic monitoring of civil engineering structures. Electron.
Lett., No. 40(14), pp. 907-908.
Pieraccini M., Fratini M., Parrini F., Pinelli G. Atzeni C. 2005.
Dynamic survey of architectural heritage by high-speed
microwave interferometry. IEEE Geosci. Remote Sens. Lett.,
No. 2(1), pp. 28-30.
Rudolf, H., Leva, D., Tarchi, D., and J. Sieber, 1999. A mobile
and versatile SAR system. In Proc. of IGARSS ‘99, Vol. 1, 28
June-2 July, Hamburg, Germany, pp. 592-594.
Schneider, D., 2006. Terrestrial laser scanner for area based
deformation analysis of towers and water damns. Proc. of 3rd
IAG Symp. of “Geodesy for Geotechnical and Structural
Engineering” and 12th FIG Symp. on Deformation
Measurements, Baden, Austria, 22-24 May. 6 pp., on CDROM.
Tarchi, D., Rudolf, H., Luzi, G., Chiarantini, L., Coppo, P., and
A.J. Sieberg, 1999. SAR interferometry for structural changes
detection: a demonstration test on a dam. In Proc. of IGARSS
‘99, Vol. 3, 28 June-2 July, Hamburg, Germany, pp. 1522-1524.
Van Gosliga, R., Lindenbergh, R., and N. Pfeifer, 2006.
Deformation analysis of a bored tunnel by means of terrestrial
laser scanning. IAPRSSIS, Vol. 36/5, pp. 167-172.
139
