NHESSDNatural Hazards and Earth System Sciences DiscussionsNHESSDNat. Hazards Earth Syst. Sci. Discuss.2195-9269Copernicus GmbHGöttingen, Germany10.5194/nhessd-2-7807-2014Earthquake-induced deformation estimation of earth dam by multitemporal
SAR interferometry: the Mornos Dam case (Central Greece)NeokosmidisS.s.neokosmidis@noa.grEliasP.https://orcid.org/0000-0002-8650-0895ParcharidisI.BrioleP.Harokopio University of Athens, Department of Geography,
Athens, GreeceNational Observatory of Athens, Institute of Astronomy,
Astrophysics, Space Applications and Remote Sensing, Athens, GreeceEcole Normale Superieure, Department of Geosciences, FranceS. Neokosmidis (s.neokosmidis@noa.gr)22December20142127807783519November20148December2014This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://nhess.copernicus.org/preprints/2/7807/2014/nhessd-2-7807-2014.htmlThe full text article is available as a PDF file from https://nhess.copernicus.org/preprints/2/7807/2014/nhessd-2-7807-2014.pdf
The scope of this paper concerns the investigation of Mornos earth Dam
(Central Greece) deformation induced by major earthquake events occur in the
broader area. For this purpose multitemporal SAR interferometry method was
used. Specifically, the technique of Differential Interferometry SBAS and
for the time series analysis the Singular Value Decomposition algorithm were
applied. The data used were ascending and descending acquisitions of
AMI/ERS-1 & 2 and ASAR/ENVISAT scenes covering the period 1993–2010. Five very
strong seismic events with epicenters close to the dam, at the same period,
were consider as potential sources of deformation. Lake level changes were
also considered as an additional factor of induced deformation. Results show
a maximum deformation rate of 10 cm along the line of sight for the whole
period. Although the observed deformation appears to be due to changes in
water level following a particular pattern, there are discontinuous over
time which coincide with specific seismic events.
Introduction
ams are multi-purpose projects having significant social and
conomic impact, such as flood control, irrigation, water
upply and electricity production. Monitoring a dam plays an
ssential role in its management and operation, especially for
nsafe conditions or problems that require appropriate
orrective measures at the early stages. Possible failure can
ause great disasters with enormous social, economic and
cological costs (Dekay et al., 1992; James et al., 2000). The
inematic behavior is directly related to the probability of
ts failure, for this reason, its monitoring is of particular
mportance.
During the last decades, remote sensing techniques (e.g. laser
scanner, differential interferometry, etc.) came to complement
the methods for measuring the displacement of infrastructures
with in-situ instruments as GPS, etc. Among these techniques,
the Differential Interferometry SAR (DInSAR) is used to measure
the micro-movements with millimeter precision. In the previous
years, in order to study the structural deformation of Mornos
dam four survey campaigns from 2002–2004 were carried out
(Gikas et al., 2005). In this paper the study of the surface
deformation, occurring in the region of the Mornos dam and the
dam itself which is based on the application of Differential
Radar Interferometry and SVD (Singular Value Decomposition)
methodologies are presented. Our study is focused on the period
of 1992–2000 and 2003–2010, exploiting
AMI/ERS-1 & 2 and
ASAR/ENVISAT, ascending and descending
acquisitions. The availability of these ascending/descending
data set allows us to discriminate the vertical and East–West
displacement components as well. The importance of the Mornos
dam, being the provider of reservoir of potable water to the
greater metropolitan area of Athens, supporting 4.5 million
people daily along with the fact that it is located in
a seismically active area was the motivation of the current
study.
The test siteGeological setting
Mornos river with a total length of 77 km, crosses the
central mainland Greece. The sources are located on the
southern slopes of Oiti, descending towards the south draining
the basin located between Giona, Vardousion and Lidoriki and
flows into the limits of the Gulf of Corinth and Patras, west
of Nafpaktos.
The artificial lake of Mornos (Fig. 1), 7 km west of
Lidoriki was built to meet the ever growing needs for water
supply of Athens. The total surface of the lake, which is the
average level, is about 15.5 km2 making it the
ninth largest artificial lake in Greece.
The main geological formations of the area belong to the
External Hellenides, namely the Parnassos-Giona, Vardousia and
Pindos geotectonic units. The area in which the dam was
constructed consists exclusively of flysch, formation of Pindos
unity.
The right (north) dam's abutment is characterized by low-grade
formations due to intense tectonism. In the left (south)
abutment, dominated by sandstones (flysch sandstone phase)
which are mainly medium-layered with thin intercalations of
siltstone and are generally corrugated aspects of large-scale.
Dam description
The construction of Mornos Dam began in 1969. The dam is
located in the Mornos River, about 220 km north-west of
Athens and is one of the largest earthen dams in Europe. The
repletion of the reservoir began in 1979 and all works were
completed by 1981. It is a large earth dam with a medium size
central clay core. It is 126 m high, the crest length
is 815 m and its width from toe to toe is 660 m
(Fig. 2). It forms a man-made reservoir with surface area of
18.5 km2 and watershed area of
560 km2. Its maximum capacity is
764 millionm3 of water, while its operational
volume is 630 millionm3. With the installation of
pumping units an additional 70 millionm3 of water
can be abstracted. The embankment component aggregates, which
vary in size from sand particles to gravels, consist mainly of
sedimentary (limestone, sandstone and shale) rocks (Lahmeyer,
1976). The lake has a maximum depth exceeding 100 m and
an average depth of 52 m (Papadimitrakis and Karalis,
2009). It consists of two sub-basins (Fig. 3) communicating
through a narrow strait. Mornos River as well as a number of
streams discharge into the Lake.
Seismic hazard of the broader area
In the surrounding area of the dam several seismic events over
5.0 Mw (Fig. 4a and b) have occurred, within the
temporal range covered by this study. Particularly:
The June 1995 Aigio earthquake
On 15 June 1995, an earthquake of moment magnitude
6.4 Mw occurred in the western part of the Gulf of
Corinth, Greece, (Fig. 4a) causing the loss of 26 human lives
and inflicting considerable damage mainly in the northern part
of Peloponnesus. The earthquake was located according to the
National Observatory of Athens about 12 km to the NNE
of Aigion, under the northern coast of the Gulf and
23 km SSE of Mornos Lake. The Harvard solution (HRV,
1995) is an East–West striking, almost pure normal fault with
a dip angle of 45∘ (Bernard et al., 1997).
The April 2007 Trichonis earthquake
During April 2007, a seismic swarm took place in the area of
Trichonis Lake (W. Greece), 43 km West of Mornos Lake
(Fig. 4a). The swarm began with small events, on 9 April and
two days later the three strongest events of the entire
sequence occurred, with sizes ranging from 5.0 to
5.2 Mw located in the southeastern part of Trichonis
Lake. The seismic activity continued for a month with smaller
magnitude events (Evangelidis et al., 2008; Kiratzi et al.,
2008). This seismic activity was not correlated with any of
the two fault zones at the northern and southern edges of the
lake but with two unmapped NNE–SSW and NW–SE faults along
its eastern shore (Evangelidis et al., 2008; Kiratzi et al.,
2008; Sokos et al., 2010a).
The June 2008 Movri earthquake
On 8 June 2008, an earthquake of 6.5 Mw and depth
17.5 km struck NW Peloponnesus (Fig. 4a). The
epicenter was located in the wider Andravida area (Movri),
30 km SW from the city of Patras and 82 km SW
of Mornos lake. The horizontal deformation filed was extended
even far away the epicenter (Serpetsidaki et al.,
2014). According to the moment tensor solutions for the
earthquake issued (NOA, HARV, INGV, USGS, ETHZ, AUTH) and the
geographical distribution of its aftershocks, the fault
strikes NE–SW, dips ∼85∘ NW while the motion
was right-lateral with small reverse component. (Papadopoulos
et al., 2010). It was felt throughout Peloponnesus, in Western
Greece and in Attica and especially in the city and the
suburbs of Patras. It triggered a number of landslides and
rockfalls, toppled old buildings and poorly reinforced houses
and cracked reinforced concrete buildings in nearby
communities. No evidence of surface rupture or significant
surface deformation based on field work was observed (Briole
et al., 2008).
The December 2008 Amfiklia earthquake
On the 13 December 2008, 08:27 GMT, an earthquake measuring
5.1 Mw occurred at about 10 km SE of the town
of Lamia in central Greece (Fig. 4a), close to the small town
of Amfiklia and 40 km NE of Mornos Lake. Despite its
moderate magnitude the earthquake caused minor damage (mostly
cracks and plaster falls) in Amfiklia and nearby
villages. Limited landslides were also observed and as
a consequence traffic in one country road was interrupted for
a few hours. Epicenters of this small sequence are gathered on
top of the south facing slope of the topographic high to the
north of Amfiklia. Known large faults have been mapped to the
north and dip to the north. In this frame, the 2008 sequence
appears to be related to a small, antithetic to the known
large faults, structure that bounds the Gravia–Amfiklia
depression to the north (Ganas and Papoulia, 2000; Roberts and
Ganas, 2000).
The January 2010 Efpalion earthquake
On 18 January 2010, 15:56 UTC, an 5.1 Mw (National
Observatory of Athens; NOA) earthquake occurred near the town
of Efpalion (western Gulf of Corinth, Greece) (Fig. 4a), about
10 km to the east of Nafpaktos, along the north coast
of the Gulf and 20 km SSW of Mornos Dam. Another
strong event occurred on 22 January 2010, 00:46 UTC with
5.1 Mw (NOA) approximately 3 km to the NE of
the first event. The two largest events were accompanied by
a sequence of aftershocks which lasted almost six months.
Both M5+ shocks exhibited normal faulting along ∼ E–W
trending planes. The first event ruptured a blind,
north-dipping fault, accommodating north–south extension of
the Western Gulf of Corinth. The dip direction of the second
event is rather unclear, although a south dip plane is weakly
imaged in the post-22 January 2010 aftershock distribution
(Sokos et al., 2010b).
SAR data used and interferometric processing
At the present work archived data from AMI (Active Microwave
Instrument) and ASAR (Advanced Synthetic Aperture Radar)
active sensors mounted on ERS-1 & 2 and ENVISAT
satellites operated by European Space Agency (ESA) were
exploited for the interferometric analysis.
A total number of 128 Single Look Complex (SLC) acquisitions
of mode I2 (incidence angle ∼23∘), with VV
polarization operating in C-band, covering an area of
100 km by 100 km were used. Among them, for
the period 1992–2000, a number of 20 ascending and 40
descending acquisitions were acquired by AMI active
sensor. Moreover, for the period of 2003–2010, a number of 29
ascending and 39 descending acquisitions were acquired from
ASAR active sensor. High accuracy orbital data from DELFT
Institute (NL) for Earth-Oriented Space Research (DEOS)
(Scharoo and Visser, 1998) were obtained for ERS-1 & 2
satellites. Moreover, high accuracy orbital data from Doppler
Orbitography and Radio-positioning Integrated by Satellite
(DORIS) instrument were obtained for ENVISAT satellite. The
topographic phase was simulated based on SRTM V3 DEM of
approximate 90 m spatial resolution.
In order to relate the pattern of the deformation with
possible sources of deformations, seismological data for the
period 1992–2010 for the Mornos region and the wider area,
which are available from the website of European Mediterranean
Seismological Centre (EMSC) and the Institute of Geodynamics,
National Observatory of Athens (NOA) as well as data of the
water level of the Mornos artificial Lake given by the Athens
Water Supply and Sewerage Company (EYDAP SA) were used.
In the present study we have applied the DInSAR technique,
which is based on exploiting the phase difference
(interferogram) between pairs of SAR observations acquired at
different time slots; this allow us to extract information of
the displacements projected to the radar Line Of Sight
(Gabriel et al., 1989; Massonnet et al., 1993). Particularly,
the Small Baseline Subset methodology (Berardino et al., 2002)
that relies on an appropriate combination of the DInSAR
interferograms by using subsequently acquired SAR data, was
used. Moreover, to reveal the deformation history, Singular
Value Decomposition (SVD) method was also applied (Berardino
et al., 2002; Usai, 2002). The SVD method connects independent
subsets of SAR acquisitions separated by large spatial
baselines, thus increasing the number of data used for the
analysis of the area of interest (Manzo et al., 2005). Gamma
processing software was used for processing and manipulating
SAR data (Wegmuller et al., 1998) ran at Linux operated
system.
Two separate processing procedures were carried out for AMI
and ASAR datasets. All the interferometric pairs were
multilooked by a factor of 1 in range and 5 in azimuth
direction. The data set was co-registered to a single master
scene, obtaining co-registration accuracies for the slaves
less than 0.06 pixels in range and 0.2 pixels in
azimuth. A subset of the full image frame was selected, by
cropping the co-registered scenes to the Area of Interest
(AOI).
The topographic component was removed to produce the
differential interferograms (referred as interferograms
hereafter). The interferometric pairs are characterized by
small spatial and temporal baselines in order to limit the
noise components usually referred to as decorrelation
phenomena (Zebker and Villasenor, 1992). For the period of AMI
acquisitions (1992–2000), spatial perpendicular baselines up
to 300 m and temporal baselines up to 3 years for the
ascending as well as up to 250 m and up to 2 years for
the descending track were selected to form a sufficient
network. For the period of ASAR acquisitions (2003–2010),
spatial perpendicular baselines up to 300 m and
temporal baselines up to 3 years for the ascending as well as
up to 300 m and up to 2 years for the descending track
were selected (Fig. 5). Particularly, 41 AMI interferograms
were produced from the ascending and 134 from the descending
track. Moreover, 71 ASAR interferograms were produced from the
ascending and 171 from the descending track. The
interferograms were further analyzed and filtered using
adaptive filters (Goldstein and Werner, 1998).
The interferograms were unwrapped using the minimum cost-flow
algorithm (Constatini, 1998). The threshold for the average
coherence was set to 0.3. The reference point was carefully
selected in order to avoid biases which can lead to shifts in
the deformation patterns. It was located on stable ground
7 km East–Northeast of the dam area, in Lidoriki
village, near LIDO permanent GPS station from Corinth Rift
Laboratory network – CRL (http://crlab.eu). The
velocity of LIDO for east, north and up components is 11.3,
0.3 and -0.3mmyr-1 respectively
(http://ngpros.space.noa.gr). The estimation of the
temporal evolution of the deformation is calculated by using
a weighted least-squares algorithm that minimizes the sum of
squared weighted residual phases.
Interferometric results and temporal comparison with
relevant seismic events
The final products were projected to Universal Transverse
Mercator (UTM) projection and superimposed over the shaded
relief.
Due to the fact that the sensor incidence angle is ∼23∘ and the LOS vector is more sensitive to vertical
displacement when we refer to uplifting/subsidence in single
track solutions, we make the assumption that the direction of
deformation is vertical. Moreover, negative velocities do not
necessarily represent subsidence, but possibly slower rates
towards the satellite respecting the reference point.
Temporal ground deformation for period 1992–2000,
during AMI acquisitions
The deformation maps of ascending (Fig. 6a) and descending
(Fig. 6b) tracks as well as the time series deformation
measurements for specific points on the dam are presented
herein.
In Fig. 6a it is indicated that generally the relative
velocities towards and away from the satellite along the LOS,
varied between maximum values of +10 and
-10mmyr-1, respectively. Particularly, an area
along the lake shore “A” across from Lidoriki village was
uplifting 5 mmyr-1 while higher to the mountain
Vardousia a subsidence of 2 mmyr-1 was
measured. Moreover, there is an area at the Giona Mountain “B”
that was subsiding up to 8 mmyr-1 and perhaps it
is due to landslide phenomena. Focusing on the dam the left – North abutment seem stable with a slight uplift towards the
dam in the range of 2 mmyr-1, while the right – South abutment and the upstream side of the dam were
considered stable.
In Fig. 6b the relative velocities towards and away from the
satellite along the LOS varied between maximum values of +12
and -12mmyr-1, respectively. Particularly an
area along the foothills of Giona Mountain “A” remains stable
but at higher altitudes an uplift of about 3 to
5 mmyr-1 is observed. Moreover there is an area
“B” at the Vardousia Mountain subsiding 4 to
6 mmyr-1. Focusing on the area of the dam, both
the abutments are characterised as stable with a small
subsidence of 1 mmyr-1 while the downstream side
of the dam is subsiding 7 mmyr-1.
Time series analysis diagrams by means of SVD for specific
point targets (Fig. 7) on the downstream side of the dam were
plotted (Fig. 8). We selected the downstream side because of
the orientation (westward) and the more coherence pixel and
this is because when the satellite travels in a descending
orbit, views a target area looking westward (in right-looking
mode).
In Fig. 8, the deformation pattern of all points is
similar. However, the deformation rate is directly related to
the level of the artificial lake. During specific time
periods, where the level of the artificial lake is increasing,
either because of rainfall or due to the water drained from
Evinos dam, the (Mornos) dam was subsiding, while during
periods where the level of the lake is reduced, the dam was
uplifting. However, during the period from 3 June 1995 to
17 September 1995 (indicated by black circle) the dam was
expected to remain stable due to the constant level of the
lake but instead it presented a deformation of -3cm
overall. This effect was probably due to the strong Aigion
earthquake (6.2 Mw) occurred on 15 June 1995 and may
affected locally the response of the dam. The correlation
between the level of the artificial lake and the deformation
in the dam is about 0.66.
Temporal ground deformation for period 2003–2010, during ASAR acquisitions
The deformation maps of ascending (Fig. 9a) and descending
(Fig. 9b) tracks as well as the time series deformation
measurements for specific points on the dam (Fig. 7) are
presented herein.
In Fig. 9a, the relative vertical velocities towards and away
from the satellite along its LOS, varied between maximum
values of +6 and -9mmyr-1,
respectively. Particularly, there is an area along the lake
shore “A” across from Lidoriki village uplifting
3 mmyr-1 while higher to the mountain Bardousia
a subsidence of 1.5 mmyr-1 was measured.
Furthermore, North for the Bardousia, there is an area “B”
subsiding 7 to 9 mmyr-1. This may be due to
landslides phenomena or neotectonic movements in the
area. Focusing on the area of the dam we observed that along
the left – North abutment a dissimilar deformation was
existed with a subsidence rate of 1 mmyr-1 near
the dam, at the middle of the abutment an uplift of
2.5 mmyr-1 and again a subsidence of
1 mmyr-1 at the end. This was probably due to the
different geological formation which caused landslides
phenomena. The right – South abutment was characterised as
stable and the upstream side of the dam presented a subsidence
of 2 mmyr-1.
In Fig. 9b the relative velocities towards and away from the
satellite along its LOS, varied between maximum values of
+10 and -12mmyr-1, respectively. An area
along the foothills of the Giona Mountain “A” was uplifted
2 mmyr-1 and in higher altitudes a subsidence of
about up to 5 mmyr-1 was observed. This may be
due to tropospheric phenomena. Focusing on the area of the dam
the left – North abutment had the same deformation pattern as
in ascending track while the right – South abutment was
uplifting 2 mmyr-1. The downstream side of the
dam presented an uplift of 4 mmyr-1.The
deformation pattern was the same for all points (Fig. 10) and
the deformation rate was related to the level of the
artificial lake. In periods where the lake level is
increasing, the dam was subsiding and during the decrease of
the level of the lake, the dam was uplifting
respectively. However, during specific periods this behavior
did not taken place. From 11 February 2007 to 5 August 2007
(left dashed circle) and 22 December 2009 to 3 October 2010
(right dashed circle) the relationship of the deformation rate
and the level of the lake was vice versa. This effect was
probably due to strong earthquakes occurred on 10 April 2007
in Trichonis lake (5.2 Mw) and on 18 January 2010 in
Efpalio (5.3 Mw). They may affected locally the
response of the dam. A more remote and stronger earthquake
occurred on 8 June 2008 in Movri (6.2 Mw) which did
not affect the response of the dam. The correlation between
the level of the artificial lake and the deformation in the
dam is about 0.29.
Decomposition of LOS deformation
Due to the availability of both ascending and descending
tracks, we could compute the east–west and vertical
components as Manzo et al. (2005) proposed. This investigation
is focused only in the Mornos dam, Fig. 11 explains the basic
rationale of this procedure.
For simplicity it is assumed that both ascending and
descending LOS directions, belong to the
East-z plane. In the Fig. 11, ϑ is
the look-angle which is assumed as the same for both ascending
and descending track. It is well known that for ERS-1 & 2
and ENVISAT satellites the look-angle is almost equal to
23∘. Moreover the reference point for both tracks
was the same. Also, P is the investigated
point target “observed” from both ascending and descending
passes and d the displacement vector
relevant to P in the East-z plane.
Based on simply geometric considerations, the east–west and
vertical displacement components are retrieved by:
dEast≈(dLOS_Desc-dLOS_Asc)/2sin(θ)dZ≈(dLOS_Desc+dLOS_Asc)/2cos(θ)
where, dLOS_Asc and
dLOS_Desc correspond to two
radar lines of sight (Manzon et al., 2005).
Decomposition of LOS Deformation, for Period
2003–2010, during ASAR acquisitions
This section presents the combination of ascending and
descending deformation maps of ASAR, in order to retrieve the
vertical (Fig. 12a) and east–west (Fig. 12b) component. This
period was chosen due to the fact that the amount of ASAR
acquisitions were more than that of AMI/ERS
(1993–2000) as well as that in this period the seismicity in
the broader area was higher. Using Eqs. (1) and (2) the maps of
UP and EAST component were created.
In Fig. 12a, the dam presents a uniform vertical deformation
of about -4mmyr-1 while at left – North
abutment there is an area where the vertical deformation is
about -7mmyr-1 while the other part has the
same rate as the dam. Probably, this area presents landslide
phenomena. The same phenomena perhaps has the right – South
abutment as the vertical deformation is about
-8mmyr-1.
Finally, in Fig. 14b, the dam presents a uniform deformation
of about 2 mmyr-1 to the West while the left – North abutment present a differential horizontal
deformation. The section near the dam and the end have
a deformation of about 2 mmyr-1 to the East while
the middle part has a deformation of about
2 mmyr-1 to the West. The right – South abutment
presents a horizontal deformation to the East as the dam.
Conclusions
Monitoring strategic structures is an activity of paramount
importance. For structures such as dams which have a high
exposure factor, continuous monitoring using satellite data
may represent one of the main non-structural countermeasures
for risk mitigation. In this research paper we have applied
a DInSAR technique using both ERS-1 & 2 AMI and ENVISAT ASAR
scenes in order to observe the surface deformation of the
Mornos dam as well as the behavior of the dam in relation to
possible sources of deformation such as seismic events and
artificial lake level. Our results show that SAR
interferometry allows mapping of very local displacements at
the dam as well as displacements on a regional scale around
the reservoir. Specifically the maximum variation of the
deformation of dam for the period 1993–2000 are about
7 cm while for the period 2003–2010 are about
4 cm. As regards the deformation in the dam the
behavior of the dam is affected mainly by the water level and
secondary by specific seismic events. As far as the
correlation between water level and deformation in the dam is
concerned, in the AMI/ERS (1993–2000) period
the correlation is 0.66 while in the
ASAR/ENVISAT (2003–2010) period is 0.29. This
difference is due to the fact that in the period 2003–2010
there were more seismic events which affected the correlation
than the previous period. No differential deformation of the
dam itself was observed, capable to raise the level of
concern.
The new very high resolution SAR sensors as RADASAT-2,
Cosmo-SkyMed but mainly TERRASAR-X and Sentinel-1A (because of
more opportunities for data provision to the scientific
community), with different incidence angles than the usual I2
mode of ∼23∘ of AMI/ERS and
ASAR/ENVISAT need to be used in order to
assess better the deformation. Geodetic GPS measurements can
be applied to validate and calibrate the results.
Acknowledgements
The authors would like to thank European Space Agency (ESA)
for the AMI/ERS and
ASAR/ENVISAT data through cat-1 6287 and
Athens Water Supply and Sewerage Company (EYDAP SA) for the
water level of the Mornos artificial lake data.
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Location map of the study area.
Cross section of Mornos Dam (Gikas et al., 2008).
Location area and bathymetry of Mornos reservoir.
(a) Location of epicenters of the main seismic events in wide area
(seismological data source: national Observatory of Athens). (b) Regional
tectonic of wide area and available earthquake focal mechanisms (Sokos et al., 2010).
ERS scenes (Upper) and ENVISAT scenes (Down) networks. (a), (b)
Relate to the AMI ascending and descending dataset respectively and (c), (d)
relate to the ASAR ascending and descending dataset.
(a) SVD/SBAS LOS deformation rates from the period 1992–2000
(sensor AMI/ERS-1&2, ascending track). (b) SVD/SBAS LOS deformation rates
from the period 1992–2000 (sensor AMI/ERS-1&2, descending track). The
location of the reference point is shown with red star. Positive values
represent deformation towards the satellite.
Selected point targets on the downstream side of the dam.
Correlation of time series deformation (1992–2000), level of
artificial lake and seismic data for selected point targets on the Mornos
dam.
(a) SVD/SBAS LOS deformation rates from the period 2003–2010
(sensor ASAR/ENVISAT, ascending track). (b) SVD/SBAS LOS deformation rates
from the period 2003–2010 (sensor ASAR/ENVISAT, descending track). The
location of the reference point is shown with red star.
Correlation of time series deformation, level of artificial lake
and seismic data at point targets on the Mornos dam.
SAR geometry in the East-z plane with the displacement vector d
(dashed line), its LOS projections dLOS_Asc and
dLOS_Desc (dotted line) and the east–west and vertical
deformation components dEast and dz (continuous line) highlighted,
respectively. A simplified ascending and descending radar geometry is
considered here, wherein we assume parallel satellite tracks, orthogonal to
the East-z plane (Manzo et al., 2005).
(a) SVD/SBAS UP component deformation rates from the period
2003–2010 (satellite ENVISAT). (b) SVD/SBAS EAST component deformation rates
from the period 2003–2010 (satellite ENVISAT).