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The rising concern on the urban vulnerability to the intensive infrastructure development requires enabling technologies offering a prompt and accurate monitoring of urban infrastructures deformation. Urban infrastructures vary dramatically both spatially and temporally and their deformation characteristics are complex. We evaluated the potential of high resolution Persistent Scatterer Interferometry (PSI) technology using coherent stacks of Spotlight mode TerraSAR-X images in monitoring the deformations of different types of infrastructures in a new economics center in China. The high density of Persistent Scatterers (PSs) was identified and therefore facilitates analyzing the deformation character of individual structures. All PSs weer categorized by identifying their corresponding ground object so as to enable to characterize deformation pattern of certain type of urban infrastructure. The spatial and temporal varying patterns of the deformations of typical building infrastructures and transportation infrastructures are revealed. They are strongly related to the interactive effects between the types, engineering structures, geometries, engineering geological settings and various loading scenarios. Besides subsidence of the ground surface, thermal dilation of the infrastructure itself might be another factor accounting for the observed deformation of infrastructure. Although the interpretation for the observed deformation patterns could be quite site-specific, high resolution PSI is shown to have the potential to reveal detailed deformation characteristics of complex urban infrastructures at a relatively large scale.
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L 2012 643
Complex Urban Infrastructure Deformation
Monitoring Using High Resolution PSI
Hengxing Lan, Langping Li, Hongjiang Liu, and Zhihua Yang
Abstract—The rising concern on
the urban vulnerability to the
intensive infrastructure development requires enabling technolo-
gies offering a prompt and accurate monitoring of urban infra-
structures deformation. Urb
an infrastructures vary dramatically
both spatially and temporally and their deformation characteris-
tics arecomplex. We evaluated the potentialofhighresolution Per-
sistent Scatterer Inte
rferometry (PSI) technology using coherent
stacks of Spotlight mode TerraSAR-X images in monitoring the
deformations of different types of infrastructures in a new eco-
nomics center in Chin
a. The high density of Persistent Scatterers
(PSs) was identied and therefore facilitates analyzing the defor-
by identifying t
heir corresponding ground object so as to enable
to characterize deformation pattern of certain type of urban in-
frastructure. The spatial and temporal varying patterns of the de-
formations of
typical building infrastructures and transportation
infrastructures are revealed. They are strongly related to the in-
teractive effects between the typ es, engineering structures, g eome-
neeringgeological s ettings and various loading scenarios.
Besides subsidence of the ground surface, thermal dilation of the
infrastructure itself might be another factor accounting for the ob-
served d
eformation of infrastructure. Although the interpretation
for the observed deformation patterns could be quite site-specic,
high resolution PSI is shown to have the p otential to revealdetailed
mation characteristics of complex urban infrastructures at a
relatively large scale.
Index Terms—Deformation monitoring, persistent scatterer in-
terferometry (PSI), TerraSAR-X, urban Infrastructure.
APIDLY swelling urban areas present a complex set of
tructure. It isc om posedo f div erse types of elem ents
arranged by humans in complex ways to residential and com-
mercial buildings, transportation systems and utiliti es [ 1] . The
timpressive engineeringconstructionin many urbanareas,
particularly i n China posts major potential vulnerability to city
subsidence [2] as the dewatering of groundwater was controlled
ctly in most of the urban areas to minimize its effect on
ground deformation [3]. Therefore, m onitoring the d eformation
of complex urban infrastructures and their impact on the ground
Manuscript received August 25, 2011; revised October 09, 2011 and De-
cember 12, 2011; accepted December 13, 2011. Date o f publication January 31,
2012; date of current version May 23, 2012. This work was supported in part by
National Science Foundation of China (41072241), National Key Technology
R&D Program (No. 2008BAK50B05).
TheauthorsarewithStateKeyLaboratory of Resources and Environ-
mental Information System (LREIS), Institute of Geographic Sciences and
Natural Resources Research, Chinese Academy of Sciences, Beijing 100101,
China (e-mail: lanhx@lre; n;;; yang
Color versions of one or more of the gures in this paper are available online
ital Object Identier 10.1109/JSTARS.2011.2181490
deformation is becoming a major
concern for the well-being of
the urban development.
However, there exist big challenges since types of urb an
infrastructure v a ry dramat
ically in both spatial and temporal
pattern. Their deformation characteristics are affected by var-
ious factors such as 3D shape, engineering str ucture, fo undation
type and geological congu
ration. Monitoring such complex
infrastructures in a large regional scale r equires enabling
technologies. The coverage of trad itional ground based survey
techniques, such as leve
ling, total station surveys and GPS,
is limited. Such point-by-point in-situ measurement is hard
to ge nerate high den se survey network required by regional
infrastructur e moni
toring [1], [4].
The advanced Persistent Scatterer Interferometry (PSI) tech-
nique is a multi-temporal radar-b ased remote-sensing techniq ue
to measure a nd monito
r surface deformation. Since the idea of
PSI was rstly introduced as PSInSAR [5], [6], various other
PSI t echniques have been developed, such as Small Baseline
Subset Approach (
SBAS) [7], Coherent Pixels Technique
(CPT) [8], Interfe rometric Point Target Analysis (IPTA ) [ 9],
Stanford Method for Persistent Scatterers (StaMPS) [10],
l Unwrapping Network algorithm (STUN)
[11], Stable Point Netwo rk (SPN) [12] and Coherent Target
Monitoring (CTM) [13]. PSI technique performs interfero-
metric phase a
nalysis only on tho se permanent scatterers (PSs)
with stable backscattering character to overcome problems
including baseline d ecorrelation, temporal decorrelation and
c di stur bance that tr adit ion al InSAR techni ques
might have difculties to deal with. PSI shows powerful capa-
bilities of precise deformatio n monitoring motions at a level
of mm/year
by simultaneously processing all the available
SAR images acquired during repeated satellite passes [14]. A
test in Las Vegas shows that ERS and TerraSAR-X d ata allow
and 30,375 respectively
[15] that conventional groun d based approaches can hardly
achieve. P SI has been p roved to be one of the most advan ced
ques for urban deformation mapping [2], [14], [16]–[25].
For mapping urban infrastructure characteristics, using PSI
technique is particularly of inter ests for discrim inating very
small s
cale features. Generally, the spatial scale for urban
infrastructures (e.g., road and bridge) may have the magnitu de
as low as several meters that can be hardly discriminated by
SAR im
ages w ith spatial resolution more than 10 meters (e.g.,
ERS-1/2, ENVISAT and JERS-1). The high density o f persis-
tent scatterers (PSs) extracted by 1-m resolution TerraSAR-X
e (i.e., tens of PSs for individual building) allows inve s-
tigating the structural deformati on of individual infrastructure
[22], [23], [25]–[27], and permits 3D and 4D reconstructions
of i
ndividual bu ild ing s [26], [28]. In addition, com pared to
1939-1404/$31.00 © 2012 IEEE
PRIL 2012
the rst generation of satellite SAR sensors (e.g., ERS-1/2
and RADARSAT-1) launched b efo re 2006, the new generation
of TerraSAR-X (X-band) Persistent Scatterer I nterferom etry
performs much better in resolving small scale geometric ambi-
guities due to lay-over, shadow, and multiple scattering effect
[14], [26]. It benets su bstantially f rom its X-band (
acquisition, different concurrent polarizat ions, high geometric
and r adiometric resolution and high revisit frequency. The
dramatic increase of PS density allows us to achieve a dense
opens promising application perspectives for complex urban
infrastructure monitoring [22], [27].
The objective of this paper is to examine how high resolu-
tion TerraSAR-X PSI may be of v alue for discriminating a wide
variety of urban infrastructure categories and mapping their de-
formation characteristics. The correspon din g urban infrastruc-
ture type of each PS point is identied r stly. Then, detailed de-
formation patterns are investigated in respect of different types
of urban i nfrastructures. T h e spatial and tempo ral deformation
characters of building and transporting infrastructures are pre-
liminarily presented and discussed to show the potential of high
resolution TerraSAR-X PSI to monitor the deformation of in-
frastructures in complex urban environ men ts.
A. Study Area
The study area Tanggu District is located in the southeast of
Tianjin (Fig. 1). It is the heartland of the “Tianjin Binhai N ew
Area”, the rising new economics center in China. As a center of
North China’s coastal area, Tanggu District has been becoming
one of the most important import/expo rt gates f or Central North
China and Northwest China. I t has been suffering from sub-
sidence since its foundation. Latest survey has shown that the
average annual settlem ent is nearly 20 mm with a maximum
value of 68 mm. Since t he dewatering of underground water
has been strictly controlled with an aim at “zero underground
exploitation” in 2014, the primary urban subsidence is there-
fore attributed to the disturbance of massive engineering in-
Fig.1. Tanggu studyareawiththe coverageof TerraSA R-X imageindicated by
a red frame. Insert map in the top-right indicates the location of Tianjin in Chin a.
Insert photo in the bottom-left shows a future view of the New International
Financial Center in Tanggu. An ongoing construction to build a 300 m high-rise
building is also presented.
frastructures. Now adays, tremendous engineering co nstructions
are taking place in Tanggu with an effort to build an Interna-
tional Financial Center (Fig. 1).
B. Data Sources
TerraSAR-X provides high resolution and short wavelength
SAR imagery at a repeat cycle of eleven days [ 29]. The most
interesting part of using TerraSAR-X images in this research
for PSI is the high resolu tio n Spotlight mod e of the sensor [26],
[27]. Therefore we used a series of TerraSAR-X repeat observa-
tions in very ne-resolution Spotlight mod e (1 m azimuth reso-
lution and 0.4 m range resolution), single polarization (VV) and
an incidence angle range of about 41 degree. Until June, 2008,
11 ascending scenes (
9.65 GHz) have been acquired (Table I).
They are also characterized by perpendicular baseline values
338 and 96 m with respect to the central refer e nce
image of March 15, 2008 (Table I). The spatial coverage of Ter-
raSAR-X scenes is shown in Fig. 1. DEM from STRM with res-
olution o f 90 m is used to generate differential interferograms.
In addition, a 0 .5 m h igh resolution optical aerial photo is used
Fig. 2. Comparison of 1-m resolution TerraSAR-X image to 0.5-m resolution
optical image.
to assist the classication of PS points. The comparison of Ter-
raSAR-X image with the optical aerial photo indicates the high
capabilities of TerraSAR-X image i n discriminating ne urban
features (Fig. 2).
The Interferometric Point Target Analysis (IPTA) technique
[9], [30], o ne of the PSI techniques, is used in processing the
time series of 1-m high resolution TerraSAR-X images. The
IPTA processing on time series o f trad itional low resolution
SAR images [19], [21], [24 ], [31]–[36] or high resolution Ter-
raSAR-X SAR images [2], [37] has been successfully used to
investigate earth surface de formations in a mm/yr scale.
Similar to other PSI techniques, the scattering stability o f
point targets in both spatial and temporal domain per mi ts inter-
pretation of interferometric phase of pairs with long baselines,
and thus makes a more complete use of the achieved data. For
large S L C data stack, a criterion of low temporal var iabi lit y and
high intensity of backscattering is adopted for the selection of
point target candidates, while low spectral diversity criterion is
used for small data stack. The differential interferometric phase
is expressed as the sum of topographic error ,de-
, atomospheric ,and terms:
The phase model indicates a linear dependence of the to-
pographic error phase on the perpendicular baseline compo-
nent. By intro ducing a constant deformation rate component, a
linear dependence of the differential interfero metric phase on
the linear deformation rate is also fo unded. Consequently, a
two-dimensional linear regression analysis of differential inter-
ferometric phase on perpendicular b aseline and time is possible,
with the slope of th e regression in dicat ing the height correction
and the linear deformation rate. For large interferogram stack,
phase unwrapping is achieved in the mean time during the re-
gression, while spatial phase unwrapping may be required be-
fore regression step for small stack. This 2D regression analysis
in the temporal domain is performed for the entire point list.
The deviation of differential interferometric phase from the re-
gression, i.e., the residual phase, is composed of nonlinear de-
formation phase, atm ospheric phase, and noise phase. Different
components of residual phase can be discriminated according
to their dissimilar spatial and temporal correlations. Parameters
can be improved stepwisely by iteratively using the obtained
parameters including height corrections, rened baselines, and
atmospheric phase to rene the phase m odel in (1).
To make the point target analysis m ore sophisticated, it is
possible to detect the quality of points and reject those poi nts
not suited for analysis according to their phase standard devi-
ation from regression, and to expand the list of points eligib le
for IPTA based on rened phase model. The outcome of pro-
cessing mai nly consists of the deformation history (both linear
and nonlinear), the corrected heights and th e atmospheric phase
for each point. It has been reported that observed deformations
might be in fact domin ated by thermal dilation for short period
monitoring (less than o ne year) in urban area [22]. Extended
phase model w ith thermal dilation co mponent considered was
also introduced in some recent studies [38], [39].
Low temporal variability criterion is not suitable to detect
PS points for small stack of images because statistical char-
acters of backscattering intensity rely on large stack of images
to be fairly revealed. As only 11 TerraSAR-X images is avail-
able in our experiment, the PS candidates were selected based
on the com bin e d use of low spectral diversity and a low tem-
poralvariability criteria to achievea balancebetween the quality
and quantity of candidates. A stack of interferograms with 56
pairs was created using multiple reference images instead of
single reference image. The use of multiple reference images
can signicantly increase the number of interferometric pairs
and therefore help to advance the reliability of regression pa-
rameters. Low spectral diversity criterion takes those well-fo-
cused point targets whose backscattering intensity almost keeps
constant when processing different looks with fractional az-
imuth and range bandwidth as PS can did ates. Th e number of
initial PS candidates i s 261,074. After iterative model rene-
ment and quality control, a total of 40,12 0 high quality persis-
tent scattere rs were identied accounting for a density of nearly
1,000 poin ts per
. In a dd ition, a large number of interfero-
metric pairs also allows phase unwrapping to be achieved during
the regression step.
The TerraSAR-X scene acquired in March 15, 2008 (im age
ID 4) was used as SLC reference geometry. Geocoding was per-
formed on the m ulti-look intensity image of the reference scene.
The geometry of d igital elevation model was also transformed
into the SAR geom etr y to assist the coregistration of images.
Offsets between the coregistered images reach below 0.1 SLC
pixel and therefore suggest very ne coregistration. Very short
baselines and temporal intervals of each TerraSAR-X interfer-
ometric pairs (Table I) facilitate the unwrapping and interpre-
tation of interferometric phase. After iterative renement of the
phasemodel and ltering analysisof the nal residual phase, the
linear and nonlinear deformation histo ries of PSs were obtained.
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Fig. 3. TerraSAR-X PSI derived deformation rates of selected PS points. The
deformation rates are divided into three levels: high, medium and low. The lo-
cations of two villages (Dongg u Petro leum N ew Village and Bohai Petroleum
New Villa ge) and f o ur infrastructur es (Nanjiang Overpass Bridge, Ha ihe Nan-
jiang Bridge, Tanggu Beach Road and Nanjiang Conveyor Belt) are illustrated.
The linear deformation rates in vertical direction of s elected
PSs are presented in Fig. 3. They have been categorized into
three classes according to the specication of China geological
disaster prevention: high (annual rate
50 mm/y r), medium
(annual rate: 20–50 mm/yr), and low (annual rate
20 mm/yr).
Points with high, medium, and low deformati on rates a re ex-
pressed with red, yellow and green respectively. It can be seen
from Fig. 3 that most of the research area present low deform a-
tion r ate, although some PS points with high defor m at ion rate
are f ound in especially Beijiang Port, Nanjiang port and south-
west region of the research area. Detailed discussion about the
deformation patterns o f different infrastructure types will be is-
sued later in this paper.
PSs have been categorized into their corresponding types of
urban ground objects (i.e. building, road, b rid ge and etc.). The
classication of PSs has to be accomplished in the rst place
for further deformation analysis in respect of certain urban in-
frastructure type. An urban map (1:2000) in the year 2008 of
the “Tianjin Binhai New Area” provided by the local governing
department is used to recognize the urban structure type that
each PS corresponds to. Overlay analysis was performed be-
tween the geocoded PS points and the urban map to classify
the PSs. The accuracy of PS classication can be improved
by rechecking the locations of PS points on the 0.5 m resolu-
tion aerial photo. T he extracted PSs from TerraSAR-X data are
then subdivided into predened urban structure categories (e.g.,
ground, building, bridge, road and etc.) and subcategories (e.g.,
high-rise, m ediu m-rise and low-rise building). The distribution
of PSs in a number of representative infrastructure categories in
the research area is shown in Fig. 4.
A. Building Infrastructure
As the most important urban infrastructure, build ing s fre-
quently suffer from severe damage caused by uneven deforma-
tion. It often results in wall cracking, oor and structure tilting
Fig. 4. Classication of PS points r egarding their corresponding urban ground
objects. Some representative classes of PSs are presented.
and even collapse. Buildings in the Tanggu D istrict are classi-
ed into three sub-categories based on the number of stories and
height, namely low-rise, m ediu m-rise and high -rise building.
The deformations of buildings in D onggu Petroleum New Vil-
lage (Donggu PNV) and Bohai Petroleum New Vi llage (Bohai
PNV) were analyzed. Their locations are indicated in Fig. 3.
Both residential and commercial buildings are located in these
two Villages. Due to different geograp hical location and geolog -
ical conditions, different characteristics of building deformation
present in these two villages. By comparing the tempo-spatial
characteristics of building PSs, it is of interest to reveal the ef-
fect of the building type, co nstruction time, geographical and
geological environment on the b uilding subsidence.
TerraSAR-X PSI monitoring results of building defo rmation
in Bohai Petroleum New Village and Donggu Petroleum New
Village are shown in Fig . 5 an d Table II. It can be seen that
over 90% of buildings in the two Villages are characterized by
slow deformation (annual deform ation rate
20 mm/yr). The
1,712 building PSs located in Bohai PNV suggest an average
annual deform ation rate of 8.9 m m/yr w ith a maxim um of 44.2
mm/yr. Donggu PNV has totally2,205 m onitoring points on the
buildings indicating an average annual deformation rate of 11.6
mm/yrwitha maximumof60.3mm/yr.The proportion ofbuild-
ings characterized by fast subsidence in Dongu PNV is larger
than in Bohai PNV (Table II). For the same type of buildings,
the average deformation rate in Bohai PNV is far less than that
in the Dogng u PNV. For example, the average deformation rate
of medium-rise buildings is 6.0 mm/yr in the Bohai PNV, while
those in D o nggu PNV show much larger average rate of 14.6
The spatial and temporal heterogeneity of building sub-
sidence was observed in both villages (Fig. 5). In Donggu
PNV, buildings located near Haihe River show much larger
deformation rate that th ose in inland regions, whil e buildings in
the so uth west part of Bo hai PNV were sinking faster than those
in northeast region. The time series deformatio n of buildings
basically exhibits linear trend, while visible non-linear defor-
mations were detected during the period from March to May,
2008 in Bohai PNV (Fig. 5).
Fig. 5 . TerraSAR-X PSI monitoring results for buildings in Donggu an d Boh ai Petroleu m New Villages. The color code of d eformation rate of Fig. 3 is ado p ted.
Figures in the righ t show the time series deformatio n histori es in different r egions.
Different types of buildings also show distinctive different
deformation characteristics (Fig. 6). The deformation rate o f
low-rise buil dings is generally more than 10 mm/yr which is rel-
atively faster com pared with medium-rise and high-rise build-
ings. For example, the typical high-rise buildings in Bohai PNV
have an average deformation rate of only 2.6 m m/yr, while the
value in Donggu PNV is 3.8 mm/yr which is slightly higher.
High rise buildings also show slightly nonlinear characters in
spite of small deformation rate (Fig. 6). M eanw hile, PSI mon-
itoring results show that large deformation occurred more fre-
quently in the corner of buildings adjacent to major roads.
The building subsidence processes are rel a ted to multiple
causative factors including engineering geological conditions,
foundation structure and construction time. As expected,
buildings are sinking much faster in the regions along Haihe
River (as shown in Dong gu PNV) an d the southwest side o f
the study region (as shown in Bohai PNV ) where soil layers
with high compressive feature and low-strength are widely
distributed. High-rise buildings usually utilize deep concrete
pile fo undation which minimizes the effect of load ing on the
underneath uncompacted soil layers and therefore are less
prone t o subsidence compared with low-rise buildings with
no concrete pile structure available for their foundations. The
Fig. 6. Time series defor mation characteristics of different types of buildings
in Donggu and Bohai PNV.
interaction bet ween building loading an d the surface geolog-
ical layers takes t im e to reach its equilibrium state. Buildings
usually demonstrate faster subsidence i n the initial stages after
construction. This mig ht explain why the building s in Donggu
PNV were sink ing faster than in Bohai PNV since Donggu
PNV i s much younger th an Bohai PNV. A nother factor that
may account f or the faster sinking rate in Donggu PNV is
that the underlaid sensitive soil layer in Donggu PNV is much
thicker than other regions and therefore exaggerates the effect
of building loading.
Thermal d ilation is another po ssible factor that might con-
tribute the diversity of defo rmation pattern of buildings. Typical
annual range of temperature in study area is about 30
would account for an expansion of 3.6 mm for a 10 m long struc-
ture if thermal dilation coefcient is assumed to be
. Our observation time (2007-12-29 2008-06-22) is ap-
proximately a span from peak winter to peak summer. In other
words, for buildings, 10 m d ifference in height cou ld probably
PRIL 2012
Fig.7. TerraSAR-XPSI Monitoringresults forNanjiang OverpassBridge. The
deformation histories of the main part and the northwest approach of the bridge
are shown in the up-right. Insert photo in the up-left also shows heavy duty
vehicle passing through.
result in 2.7 mm d ifference of therm al d e formation durin g our
observation time. Therefore, more vertical dilations of hig h-rise
buildings could be a possible explanation for their less observed
deformations compared with medium-rise and low-rise bu ild-
ings (less than 4 mm averagely, see Fig. 6). Similar correla-
tion of the observed movement with the height of bu ild ings is
also detected [40]. Unfortunately, as thermal effect m odule is
included in the phase mode of current codes, we therefore are
not able to precisely evaluate the effects of t herm al dilation on
the observed deformations.
B. Transportation Infrastructure
High resolution PSI technique is capable of recognizing
meter-scale linear features and allows performing engi-
neering-scale deformation monitoring on narrow u rban lin ear
transportation infrastructures. It helps engineers evaluate the
conditions of transportatio n infrastructure in a fast and reliable
way. The d eform ation processes of selected typical transporta-
tion infrastruc tur e s i ncluding bridge, road and linear conveying
belt w ere analyzed in this section. Their inuencing factors and
associated mechanism were also discussed.
Nanjiang Overpass Bridge is one of the two major represen-
tative b rid ges in the study area. It is located in the south of the
study area and is the i mp ortant transportation channel to Tanggu
port. It is a double-way ro ad br idge with total of six lanes and
transportation capacity of 75 tons. Totally 205 PS points were
detected over the surface of the bridge (Fig. 7). The overall av-
erage deformation rate is 15.1 mm/yr. Different parts of the
bridge are characterized by different clusters of deform ation
rates. It can be seen that main part of the bridge is relatively
stable indicated by a large number of green PS points on its sur-
face, while all the approach roads connecting to the main part
of the bridge are characterized by rapid deformation with an av-
erage rate of 31.5 mm/yr. The maximum deformation occurred
in the secti on of northwest approach bridg e with a deformation
rate up to 73.3 mm/yr as shown in Fig. 7 by a red cross. U n -
even subsidence often results in sharp height change on the road
Fig. 8. Th e diversity of deform atio n between the west part and the east part
of Haihe Nanjiang Bridge. A n interpolated map of deformation rate has been
generated based on monitoring results of PS points.
surface. As a result, vehicles are prone to jump when passing
through the intersection between the approach and main part o f
bridge. The sinking time series of both the northwest ap pro ach
and th e main bridge show primary a linear behavior (Fig. 7).
The deform ation characteristi cs of bridge are directly re-
lated to the interactive effect between vehicle loading and the
engineering structures of bridges, while thermal effect plays
minor role. Field survey has observed a shuttling of heavy duty
vehicles crossing the bridge. The slow sub siding main bridge
is equipped with the concrete pile structure, while natural soil
foundation is used in the approach sections which results in
more severe deform atio n under the s ame veh icle loading.
An obvious uneven deformation pattern was also observed on
Haihe Nanjiang Bridge which locates in adjacent east of Nan-
jiang Overp ass Bridge (Fig. 8). The east part of Haihe Nanjiang
bridge (15 PSs) shows a larger av erage deformation rate of 18.4
mm/yr with a maxim um of 27.0 mm/yr, while an average defor-
mation rate of only 4.7 mm/yr with a maximum of 10.0 mm/yr
was found in the west part of the bridge. A deformatio n map is
generated by interpolation with the 23 PS points on the bridge
(Fig. 8) for better illustration of the uneven deformation phe-
nomenon. Visible no n-linear and differential deform ation char-
acteristics are also detected between both parts of the b ridge
(Fig. 8). This might imply an existence of possib le u neven sub-
sidence hazard, although the difference within the monitoring
time is quite minor (
1 cm). Field surv ey has found a number of
large piles of raw construction materials adjacent to the east part
of b ridge. They provid e extra loadings which impact on the sta-
bility of the east part of the bridge. Considering the main bridge
over Haihe River (about 2 00 m) is sensitive to the t her mal de-
formations, the o bserv ed diversity of deformation between the
west part and the east part of this bridge (about 7 mm, see Fig. 8 )
is also possibly attribut ed to thermal dilation.
Fig. 9. TerraSAR-X PSI monitoring results for TangguBeach Road. There sec-
tions are marked on the map to present various deformation characteristics of
different road sec tions.
Tanggu Beach Road is a major transportation infrastructure
connecting the north and the south of the city. It serves as
an important gateway for transporting materials in Tianjin
Binhai New Area. The PSI deformation mo nitoring results
for t he Tanggu Beach Road is shown in Fig. 9, in which the
deformation rates of PS points are also interpolated for better
illustration. An average deformation rate of 23.2 mm/yr is
observed for the 5 km long road. The maximum annual defor-
mation (nearly 60 mm) is located at the southern intersection
between Tanggu Beach Road and Nanjiang Overpass Bridge.
Distinct spatial variation of deformation was observed along
Beach road. It can be divided into three sections (A, B and
C as indicated in Fig. 9). Section A is characterized by slow
deformation with an averag e rate of 13.9 mm/yr. Much higher
deformation rate was observed in Section B with an average
rate of 38.0 mm/yr. A number of abnormal sites can be iden-
tied in Section B indicated by red color in Fig. 9. Similar as
Section A, Section C has relatively low deformation rate with
an average rate o f 1 6.9 mm/yr. The relative larger de formation
in Secti on B more or less resulted from the d istr ibutary of
loading n ear the approach of the Nanjiang Overpass Bridge. As
this road structure principally lies perpendicular to the ground
range direction, thermal dilation, if exists, would have limited
inuences on its observed spatial deformation pattern.
Another interesting transportation infrastructure is the Nan -
jiang conveyor belt in south of Nanjiang Po rt. It is one of the
important transportat ion infr astructures for conveying mining
materials from Nanjiang Port. The PSI monitoring on Nanjiang
conveyor belt sugg ests an annual average deform atio n amount
of 16.4 mm with a maximum of 50.1 mm. The conveyor belt is
divided into three sections for further discussion (Fig. 10).
An interesting deformation pattern has been observed from
distribution of PSs and deformation prole along conveyor belt
(Fig. 10). The deformation rate goes up and down regularly
Fig. 10. H igh resolution PSI Monitoring results for Nanjian g Conveyor Belt.
There sections are illustrated in the gure to representvarious deformation char-
acteristics. Temporal patterns of deformations of the three sections are also pre-
along the conveyor belt. The distribution of engineerin g struc-
ture is found to be responsible for the sensitive uctuation of
deformation rate. The interval of deformation distribution is
closely corresponding t o the interval of the piers supporting the
conveyor belt. The stronger the piers are, e.g., the middle part
of the conveyor belt ( Sectio n B), the less the deformation takes
place. The regular uctuation of deformation rate in section A is
also possibly derived from thermal dilation which would m ake
two parts of the tracks move towards each other in the construc-
tional gaps [41] an d in turn induce distinct contrast of observ ed
deformations between adjacent points.
V. C
Rapid urbanization processes involve intensive infrastructure
development which increases the urban vulnerability to subsi-
dence.A promptand accuratemonitoring ofcom plex infrastruc-
ture deformation at a relativ ely large scale is one of the m ost
important concerns in urbanized area. In this study, P ersistent
Scatterer Interferom etry has been carried out using high resolu-
tionTerraSAR-X images tomonitorthe deformation of complex
urban infrastructures in one fast developing area.
The classication of PS points r egarding their correspondin g
urban structure ty pes was rstly accomplished for deform ation
analysis. Detailed deformation patterns of different representa-
tive types of urban infrastructures were successfully revealed.
The def or mat ion s of all in vestigated infr astructures in the study
area unanimously present a remarkable spatial and temporal
variation. The com plex ity of urban infrastructures with regard
to their types, engineering structures, geometries, construction
ages, engineering geological conditions and external loadings
results in complicated spatial-temporal defo rmation patterns of
urban infrastructures.
As expected, newer buildings and those buildings located in
relatively inferior engineering geological conditions sink much
faster. High-rise buildings show lower deformation rates com -
pared with low-rise build ings thanks to t heir stro nger pile f oun-
dation and possible larger thermal expansions.
PRIL 2012
The spatial def or mat ion patterns of linear transportation in -
frastructures were also well revealed. Especially, a rema rkable
regular uctuating pattern of deformation rate was detected
along a linear conveyor belt. The interactive effect between
external loading and the engineering structure dominates th e
deformation character of transportation infrastructure. In gen-
eral, sections of transportation infrastructures bearing heavier
loadings or supported b y more sensitive foundations are more
prone to subsidence. In addition, lateral thermal dilation is
another possible factor which would domin ate the diversities
of observed deformatio ns between different parts of infrastruc-
tures, especially for short period observations [22], [39].
The observed deformation patterns of various types of infra-
structures from TerraSAR-S PSI are comparable with o ur eld
observations. The deformation m echanism of varieties of urban
infrastructures w as in ter pret e d wit h regar d to th eir types, en -
gineering structures, geometries, geological settings, construc-
tion tim e s and exterior loadings. The spatial-temporal var ying
patterns of urban infrastructure deformatio n in a regional scale
have been revealed althoug h som e systematic deviations migh t
exist between the exact value of our m onitoring and in-situ mea-
surements like leveling.
The availability of SAR images is one possible drawback to
our results. Therefore multiple reference scenes in PSI tech-
niqueweread opted perm iting th e potential of PSI analysis using
small data stacks [42]. For example, ground d e formation in t he
urban area of Guangzhou city was successfully detected based
on 10 ASAR images [21]. I n addition, the reliability of PS clas-
sication highly relies on the backscattering characteristics of
SAR signals, accuracy of the geocoding of PS points and the ac-
curacy of the urban map. The discrepancy of coordinate systems
ofdifferentdata sources wouldintroducecoregistratio n problem
and therefore fallacious classication to some PS points.
To rev eal the temporal variation of ground deformation,
the non-linear deformation has been addressed considerably
in the PSI processing. It was obtained by excluding phase
errors (noise), atmospheric phase from the nal residual phase
generated by linear regression model. Therefore, the results
are strongly affected by the linear model. The consolidation
of linear regression model was conducted through iteratively
running linear regression analysis with rened p aram eters,
i.e. rened baselines, rened atmosphere and point height
estimates, using spatially ltered reference point. However, it
is alwa ys a challeng e to precisely discriminate the no n- linear
deformation, atmospheric effect and phase noise in the residual
phase, especially for the short temporal image stacks. For
example, the very minor component non-linear deformation
could be easily attributed to the distu rbing com po nents of phase
noises. Hence, the interpretation of both linear and non-linear
component of deformation should be performed with cautions.
A num ber of advanced functions have not been included in
the current PSI code used in this research. For example, the
quantitative analysis of potential inuences o f thermal dilation
effects o n our PSI deformation monitoring is missing due to the
unavailability of cert a in module. Employing a phase mode wit h
thermal dilation considered [ 38], [39] could help to g et more
detailed information (both dynamic and static) regarding the
deformation of infrastructures. The key element in PSI tech-
nique is to extract useful information i.e. deformation from the
original observation. Therefore the role of the “disturbing com-
ponents” has to be considered in processing and interpretation.
The robust spatial and temporal ltering technique might help
improve such discriminat ion. The exibility of selection of l-
tering window shape and length could also be a benet.
Despite of various possible disadvantages, the potential of
high TerraSAR-X PSI to monitor the deformation of complex
urban in frastructures is fairly presented in o ur experim ent.
Theauthors wish tothank TangguCenter forWaterResources
Management for the support of eld investigation and the re-
lated data, Tianjin Institute of Survey and Mapping for the sup-
port of high resolution aerial images an d Spot Image CN for the
support of TerraSAR-X SAR data.
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Hengxing Lan received the B.S. and M.Sc. degrees
in geology from Shandong University of Science
and Technology in 1995 and 1998, respectively. He
received the Ph.D. degree in geological engineering
from the Institute of Geology and Geophysics,
Chinese Academy of Sciences, in 2001.
He worked in the department of civil and envi-
ronmental engineering in Hong Kong University
in 2003 as a Research Associate. From 2004 to
2009, he was a Research Engineer in the University
of Alberta in Canada. He is currently a Professor
with the State Key Lab of Resources and Environmental Information System
(LREIS), In stitu te of Geographic Sciences and Na tur al Resources Research,
Chinese Academy of Sciences. His current research in terests a re d evelopment
and application of R e mote Sensing and GIS technology to geological hazards
Langping Li received the B.S. and M.Sc. degrees in physical geography from
Nanjing University in 2007 and 2 01 0, respectively. He is cu rrently a Ph.D. can -
didate majoring in GIS and remote sensing in the State Key Lab of Resources
and Environmental Informa tion System (LREIS), Institute of Geographic Sci-
ences and Natural Resources Research, Chinese Academy of Sciences.
HongjiangLiu received the B.S. degree in physical geography from Southwest
Normal Un iversity in 1993 . He receiv ed the M.Sc. degrees and Ph.D. degree in
physical geography from the Institute of Mountain Hazards and Environment,
Chinese Academy of Sciences, in 1993 and 2008, respectively.
He is currently a Post-Doctoral Fello w in GIS and Remote Sensing in the
State Key Lab of Resources and Environmental Information System (LREIS),
Institute of Geographic Sciences and Natu r al Resources Research, Ch in ese
Academy of Sciences.
Zhihua Yang recei ved the B.S . degree from Shandong Architect University in
2007 and the M.Sc degree in geographic information systems from the China
Geoscience University in 2010. He iscurrently a Ph.D. candidate in GISan d Re-
moteSensingintheStateKeyLabofResources and EnvironmentalInformation
System (LREIS), Institute of Geograph ic Sc iences an d Natural Reso u rces Re-
search, Chinese Academy of Sciences.
... Different sensors can be used for frequently monitoring a specific area of interest. For instance, ERS, Envisat, and Radarsat have monthly revisit time, while Sentinel, TerraSAR-X, and COSMO-SkyMed provide even weekly revisit time [11,12]. Moreover, it is also possible to map deformations which occurred in the past, if images of the site were acquired. ...
... Several studies have highlighted the potential of PS InSAR techniques in estimating the displacement of civil structures and of their thermally induced displacement that exhibits a seasonal behavior [13]. PS InSAR techniques are essentially phase model-based and assume the presence of one dominant scatterer within a resolution cell [7][8][9][10][11][12][13]: the deformation is measured only over the available coherent pixels. The deformation model usually cannot be assumed linear, especially in the case of civil structures, such as bridges, railways, and specific buildings with metallic cover, whose construction materials may be sensitive to thermal dilation effects. ...
Full-text available
Structural health monitoring and damage detection tools are extremely important topics nowadays with the civil infrastructure aging and deteriorating problems observed in urban areas. These tasks can be done by visual inspection and by using traditional in situ methods, such as leveling or using traditional mechanical and electrical sensors, but these approaches are costly, labor-intensive and cannot be performed with a high temporal frequency. In recent years, remote sensing has proved to be a very promising methodology in evaluating the health of a structure by assessing its deformation and thermal dilation. The satellite-based Synthetic Aperture Radar Tomography (TomoSAR) technique, based on the exploitation of a stack of multi-temporal SAR images, allows to remotely sense the movement and the thermal dilation of individual structures with a centimeter- to millimeter-level accuracy, thanks to new generation high-resolution satellite-borne sensors. In this paper, the effectiveness of a recently developed TomoSAR technique in assessing both possible deformations and the thermal dilation evolution of man-made structures is shown. The results obtained using X-band SAR data in two case studies, concerning two urban structures in the city of Naples (Italy), are presented.
... In this work, the application of the PSI technique to the analysis of satellite datase enabled the evaluation of the spatiotemporal distribution of displacements in a comple urban area, as it was to be expected given its well proven potential for monitoring terrai and complex infrastructure [26,43,59,60]. Regarding the test area, previous work has fo cused on regional-scale deformation to assess instability processes [61] or on the analys of negative displacements concerning the coastal plain [62], and large-scale pattern d formation in relation to tectonic, volcanic, geomorphological and anthropogenic induce processes [50,63]. ...
... In this work, the application of the PSI technique to the analysis of satellite datasets enabled the evaluation of the spatiotemporal distribution of displacements in a complex urban area, as it was to be expected given its well proven potential for monitoring terrain and complex infrastructure [26,43,59,60]. Regarding the test area, previous work has focused on regional-scale deformation to assess instability processes [61] or on the analysis of negative displacements concerning the coastal plain [62], and large-scale pattern deformation in relation to tectonic, volcanic, geomorphological and anthropogenic induced processes [50,63]. ...
Full-text available
In the absence of systematic structural monitoring to support adequate maintenance standards, many existing infrastructures may reach unacceptable quality levels during their life cycle, resulting in significant damage and even potential failure. The metropolitan area of the Gulf of Salerno (Italy), served by a complex multimodal transport network connecting the port area to the roads and railways surrounding the urban area, represents an important industrial and commercial hub at the local and international scale. This particular scenario, developed in a complex morphological and geological context, has led to the interference and overlapping of the transport network (highway, railway, main and secondary roads) that run through the piedmont area north of the port. Given the relevance of the area, our research aims to highlight the capabilities of the persistent scatterer interferometry (PSI) technique, belonging to the group of differential interferometric synthetic aperture radar (SAR), to extract space–temporal series of displacements on ground points or artifacts with millimeter accuracy useful to understand ongoing deformation processes. By using archived data from the European Space Agency missions, i.e., ERS1/2 (European remote-sensing satellite) and ENVISAT (environmental satellite), and the most recent data from COSMO-SkyMed constellations, it was possible to collect a 28-year dataset that was used to spatially analyze displacement patterns at a site-specific scale to check the stability of viaducts and embankments, and on a larger scale to understand the activity of the surrounding slopes. Despite the different resolution and subsequently the ground density, the analysis of the different datasets showed a spatiotemporal consistency in the displacement patterns that concerned two subareas showing significant annual velocity trends, one northeast of the city and the second in the port area. The analysis presented in this paper highlights how a complex geologic area, combining slope movements and various fault systems, could be a major concern for the stability of the overlying infrastructure and also the role that a PSI analysis can play in remotely monitoring their behavior over long periods of time.
... Permanent scatterer interferometry (PSI), also referred to as PSInSAR, has significant advantages in large-scale surface displacement monitoring; examples of these benefits include the use of persistent scatterers, the elimination of atmospheric effects, the high accuracy of deformation measurements (on the millimeter scale), and the ability to acquire time series deformation, which considerably improve the efficiency of surface deformation monitoring. More recently, highly sophisticated PSI techniques have been shown to be capable of maximizing the spatial density of measurement points by taking advantage of different scattering mechanisms [111,112]. For example, the SqueeSAR technique, a second-generation PSInSAR algorithm, is based on the processing of long time series of coregistered SAR images acquired over the same target area from the same acquisition geometry and can more effectively obtain displacement data. ...
Full-text available
Monitoring and early warning systems for landslides are urgently needed worldwide to effectively reduce the losses of life and property caused by these natural disasters. Detecting the precursors of giant landslides constitutes the premise of landslide monitoring and early warning, and remote sensing is a powerful means to achieve this goal. In this work, we aim to summarize the basic types and evolutionary principles of giant landslide precursors, describe the remote sensing methods capable of identifying those precursors, and present typical cases of related sliding. Based on a review of the literature and an analysis of remote sensing imagery, the three main types of remote sensing techniques for capturing the geomorphological, geotechnical, and geoenvironmental precursors of giant landslides are optical, synthetic aperture radar (SAR), and thermal infrared methods, respectively. Time-series optical remote sensing data from medium-resolution satellites can be used to obtain abundant information on geomorphological changes, such as the extension of cracks and erosion ditches, and band algebraic analysis, image enhancement, and segmentation techniques are valuable for focusing on the locations of geomorphological landslide precursors. SAR sensors have the ability to monitor the slight slope deformation caused by unfavorable geological structures and can provide precursor information on imminent failure several days before a landslide; furthermore, persistent scatterer interferometric SAR has significant advantages in large-scale surface displacement monitoring. Thermal infrared imagery can identify landslide precursors by monitoring geoenvironmental information, especially in permafrost regions where glaciers are widely distributed; the reason may be that freeze–thaw cycles and snowmelt caused by increased temperatures affect the stability of the surface. Optical, SAR, and thermal remote sensing all exhibit unique advantages and play an essential role in the identification of giant landslide precursors. The combined application of these three remote sensing technologies to obtain the synthetic geomorphological, geotechnical, and geoenvironmental precursors of giant landslides would greatly promote the development of landslide early warning systems.
... The SBAS technique uses the Delaunay MCF phase unwrapping method to smooth the elevation information of the entire surface, while the phase unwrapping of PS InSAR preserves the elevation information by analyzing the permanent scatterers separately. Therefore, the elevation accuracy obtained by PS-InSAR in this study will be higher than that of SBAS [47,48]. However, similar to the surface settlement caused by the change in groundwater level, it belongs to a non-linear deformation. ...
Full-text available
Geological disasters caused by surface deformation are common, especially in urban areas, which seriously impede urbanization’s sustainable development. Monitoring and analysis with high spatial and temporal resolution are particularly important to assess the risk of geological disasters caused by urban deformation. This study uses Sentinel-1A satellite imagery to obtain the surface deformation time series of Nanchang City based on SBAS-InSAR and PS-InSAR techniques and is combined with wavelet period analysis and gray correlation analysis to determine the correlation between deformation area and climate environment. This study shows that there was a large-scale subsidence trend in the central urban area of Nanchang in those two years, and an uplift trend in the agro-ecological areas in the southeast. A periodic analysis further shows that the areas with larger changes in surface deformation are more affected by changes in precipitation. This study, integrated with external data, examines the possibility of subsidence disasters occurring along subway lines in areas with large deformation magnitudes from multiple angles.
... The Differential Synthetic Aperture Radar Interferometry (DInSAR) technology has been established as a powerful geodetic tool applied in various fields of earth science and engineering (Teatini et al., 2005;Vilardo et al., 2009;Zhang et al., 2012;Lan et al., 2012;Zhao et al., 2015). This non-contact technique outperforms the conventional survey methods due to the unique advantages of intensive detectable measurements, high monitoring precision, and routine inspection capacity without installing equipment or accessing the study area (Chang and Hanssen, 2014;Shamshiri et al., 2014;Milillo et al., 2016). ...
... ese InSAR techniques have been used in a wide range of deformation monitoring applications, such as urban ground settlement [31][32][33], mine subsidence [34][35][36][37][38][39][40][41], earthquakes and plate movements [42][43][44][45], volcanic eruptions [46][47][48], infrastructure deformation [49][50][51], glacial drift [52][53][54][55], permafrost deformation [56][57][58][59][60], and landslides [61][62][63]. Compared to other MT-InSAR techniques, SBAS-InSAR has the advantage of being able to overcome atmospheric interference and requires a relatively small amount of data [14,16,21]. ...
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The fragile habitat of alpine mining areas can be greatly affected by surface disturbances caused by mining activities, particularly open-pit mining activities, which greatly affect the periglacial environment. SBAS-InSAR technology enables the processing of SAR images to obtain highly accurate surface deformation information. This paper applied SBAS-InSAR technology to obtain three years of surface subsidence information based on the 89-scene Sentinel-1A SLC products, covering a mining area (tailings and active areas) in the Tianshan Mountains and its surroundings from 25th December 2017 to 2nd January 2021. The data were adopted to analyze the characteristics of deformation in the study region and the mining areas, and the subsidence accumulation was compared with field GNSS observation results to verify its accuracy. The results showed that the study area settled significantly, with a maximum settlement rate of −44.80 mm/a and a maximum uplift rate of 28.04 mm/a. The maximum settlement and accumulation of the whole study area over the three-year period were −129.39 mm and 60.49 mm, respectively. The mining area had a settlement value of over 80 mm over the three years. Significantly, the settlement rates of the tailings and active areas were −35 mm/a and −40 mm/a, respectively. Debris accumulation in the eastern portion of the tailings and active areas near the mountain was serious, with accumulation rates of 25 mm/a and 20 mm/a, respectively, and both had accumulation amounts of around 70 mm. For mine tailing pile areas with river flows, the pile locations and environmental restoration should be appropriately adjusted at a later stage. For gravel pile areas, regular cleaning should be carried out, especially around the mining site and at the tunnel entrances and exits, and long-term deformation monitoring of these areas should be carried out to ensure safe operation of the mining site. The SBAS-InSAR measurements were able to yield deformations with high accuracies over a wide area and cost less human and financial resources than the GNSS measurement method. Furthermore, the measurement results were more macroscopic, with great application value for surface subsidence monitoring in alpine areas. 1. Introduction Mining activity can cause surface deformations and negatively impacts the environment [1, 2]. If rehabilitation measures are not handled properly, they can lead to serious subsequent disasters such as mine collapse [3], slope instability [4], vegetation death over large areas [2, 5], and severe water-soil erosion [3]. These potential threats and problems are more prominent in high-altitude areas due to the fragile habitats therein [2]. The key to solving these problems is to provide theoretical support for decision-making based on a large amount of basic data such as surface deformation data. Ground settlement [6] data provide an understanding of changes in mining areas and the surrounding environment, contributing to their sustainable development. Subsidence data can also provide synchronous information on how to develop in areas containing perilous rocks, providing a basic foundation for mining safety in cold-plateau regions. In recent years, with the development of computer technology, remote sensing (RS), and geographic information system (GIS) technology [7–9], increasingly more novel geographic analysis methods [10–12] have been used for the dynamic monitoring of surface subsidence in mining areas, among which monitoring based on interferometric synthetic aperture radar (InSAR) technology [13–15] has performed excellently. One of the advantages of InSAR over traditional time-consuming and costly monitoring methods, such as level measurements and global positioning satellite (GPS) measurements, is that it has all-day, all-weather [13, 16] observation capability. Moreover, microwaves can effectively penetrate the atmosphere and are less affected by water vapor and surface vegetation [17]. In addition, as more and more synthetic aperture radar (SAR) satellites have been launched, increasingly more materials are accessible [16, 18–21], and the data acquisition cycles have become shorter. As a result, the accuracy of these measurements has greatly improved. InSAR has the added advantage of obtaining ground deformation information over large areas at a relatively small cost. As a corollary, deformation measurements based on InSAR have becoming increasingly popular [21]. So far, InSAR technology has evolved from traditional differential interferometric synthetic aperture radar (D-InSAR) [22, 23] to multitemporal InSAR (MT-InSAR) [24] technologies, including persistent scatterer InSAR (PS-InSAR) [25–27], small baseline subsets InSAR (SBAS-InSAR) [28], and distributed scatterer InSAR (DS-InSAR) [29]. In addition, to compensate for the deficiency that D-InSAR or MT-InSAR can only acquire line-of-sight (LOS) direction deformation, the multiaperture InSAR (MAI) [30] technique has been proposed to acquire deformation information in the azimuthal direction (i.e., satellite flight direction). These InSAR techniques have been used in a wide range of deformation monitoring applications, such as urban ground settlement [31–33], mine subsidence [34–41], earthquakes and plate movements [42–45], volcanic eruptions [46–48], infrastructure deformation [49–51], glacial drift [52–55], permafrost deformation [56–60], and landslides [61–63]. Compared to other MT-InSAR techniques, SBAS-InSAR has the advantage of being able to overcome atmospheric interference and requires a relatively small amount of data [14, 16, 21]. This method has been widely used for surface deformation monitoring with excellent results [28, 31–63]. For the above reasons, to understand the dynamic changes of subsidence in alpine mining areas, this study focuses on a mining area in the Tianshan Mountains of China as the research object, which consists of 89 scenes of Sentinel-1A level-1 single look complex (SLC) data processed via SBAS-InSAR technology to obtain the surface subsidence [35] information of the area. The subsidence information is analyzed to understand surface subsidence around the mining site and to provide recommendations for mining activities. The cumulative deformation information is also compared with data obtained from in situ global navigation satellite system (GNSS) measurements to verify the accuracy of SBAS-InSAR technology for surface deformation monitoring and subsidence measurements in alpine mining areas. From this, the extent of impact of mining activity on local environment can be understood. In addition, the obtained deformation over a large area can be used as fundamental information to provide a theoretical basic for mining policy, which is of great value to ensure environmental sustainability. 2. Regional Characteristics The study area (Figure 1) is located in the eastern Tianshan Mountains, with geographical coordinates of 84.95–85.12°E and 43.28–43.35°N (as shown by the red box in Figure 1(a)). Its altitude ranges from 3,160 m to 4,365 m above the sea level (m.a.s.l.), with an average altitude of 3,839 m. The annual temperature has a maximum of 16°C and a minimum of −30°C [2], and it is a typical high-cold and high-altitude area. The snowline is 3,700–3,900 m.a.s.l., and the areas above the snowline are covered with glaciers, snow cover, permafrost, rock glaciers, and other periglacial geomorphology. The watershed located in the southwest of the mining area divides the rivers into two basins flowing south and north [9]. The south-flowing rivers converge with the Yili River, which is dominated by small rivers. The north-flowing rivers empty into Noor Lake, which eventually feeds into the Manas River. The maximum daily precipitation is 146 mm, the annual rainfall exceeds 1,000 mm, the evaporation is 425 mm, the maximum wind speed is 12 m/s, the average humidity is about 43%, and the wind direction is mainly north-northeast [2]. From October to April, the average temperature is below freezing, and solid precipitation such as hail and snowfall dominates this period. In contrast, from July to September, there is relatively little snowfall and warmer temperatures, making this the season appropriate for grass growth.
... The implementation of a suitable method to periodically control infrastructure networks at different scales of analysis is also a key challenge: it may constitute an effective tool for remotely monitoring environmental risks and for planning mitigation measures. Several in situ techniques are available for the local monitoring of infrastructure assets, including manual visual inspection, levelling, total station surveying, and GPS technologies (Lan et al., 2012). These approaches provide highly accurate measurements of deformation at a single point, but can be highly expensive if a high density of measurements suitable for wide-scale infrastructure monitoring is required. ...
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The Italian territory is strongly affected by ground instability phenomena and the occurrence of geological events, such as landslides and subsidence, is one of the main causes of damage to linear infrastructures, such as roads, bridges, railways and retaining walls, resulting in important socio-economic and human losses. To this aim, the frequent and accurate monitoring of surface displacements plays a key role in risk prevention and mitigation activities. In the last decade, a considerable interest towards innovative approaches has grown among the scientific community and land management institutions. In particular, Differential Interferometry Synthetic Aperture Radar (DInSAR) technique represents a useful tool to provide information on temporal and spatial evolution both of ground instability phenomena and of their interaction with man-made facilities, thanks to its accuracy, high spatial resolution, non-invasiveness and long-term temporal coverage, at reasonable costs. In this work, a GIS-semiautomatic approach, using Synthetic Aperture Radar data acquired by COSMO-SkyMed sensor, has been successfully applied to detect landslide-induced effects in terms of deformations of a linear infrastructure interested by slow-moving landslides in Campania Region (Italy).
The coalfield in the northwest suburbs of Xuzhou has suffered from extensive land subsidence; however, the temporal nonlinearity and corresponding spatial variation of its surface deformation has not been adequately explored. This study revealed complex surface deformation of the study area from 2015 to 2020 using time series InSAR. A general trend from sharp subsidence to moderated subsidence or even uplift is observed. Three main characteristic types of deformation time series, namely “Subsidence (S)”, “Subsidence–Uplift (S-U)” and “Subsidence–Uplift–Subsidence (S-U-S)”, were detected. Generally, mining activities control the fundamental constraining factors for the surface deformation. Mine closures affect the date of reversal from subsidence to uplift, or in other places the return to subsidence after uplift. Higher deformation rates in preceding sections of the deformation time series are generally correlated with later reversals of deformation trend and higher deformation rates of the succeeding sections of the time series. However, universally applicable spatial and temporal patterns of deformation were not detected, suggesting that surface deformation in the study area is a very complex process. Detailed process and mechanism analysis of surface deformation in the study area should focus on specific mines and pay particular attentions on dewatering and subsequent flooding of mines.
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Loess covers approximately 6.6% of China and forms thick extensive deposits in the northern and northwestern parts of the country. Natural erosional processes and human modification of thick loess deposits have produced abundant, potentially unstable steep slopes in this region. Slope deformation monitoring aimed at evaluating the mechanical behavior of a loess slope has shown a cyclic pattern of contraction and expansion. Such cyclic strain change on the slope materials can damage the loess and contribute to slope instability. The site showing this behavior is a 70-m high loess slope near Yan'an city in Shanxi Province, northwest China. A Ground-Based Synthetic Aperture Radar (GB-SAR) sensor and a displacement meter were used to monitor this cyclic deformation of the slope over a one-year period from September 2018 to August 2019. It is postulated that this cyclic behavior corresponds to thermal and moisture fluctuations, following energy conservation laws. To investigate the validity of this mechanism, physical models of soil temperature and moisture measured by hygrothermographs were used to simulate the observed cyclic deformations. We found good correlations between the models based on the proposed mechanism and the exhibited daily and annual cyclic contraction and expansion. The slope absorbed energy from the time of maximum contraction to the time of maximum expansion, and released energy from the time of maximum expansion to the time of maximum contraction. Recoverable cyclic deformations suggest stresses in the loess are within the elastic range, and non-recoverable cyclic deformations suggest damage of the loess material (breakage of bonds between soil grains), which could lead to instability. Based on these observations and the models, we developed a quantitative relationship between weather cycles and thermal deformation of the slope. Given the current climate change projections of temperature increases of up to 3.5 °C by 2100, the model estimates the loess slope to expand about 0.35 mm in average, which would be in addition to the current cyclic "breathing" behavior experienced by the slope.
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Among different sets of constraints and hazards that have to be considered in the management of cities and land use, land surface subsidence is one of the important issues that can lead to many problems and its economic consequences cannot be ignored. In this study, the ground surface deformation of Gävle city in Sweden is investigated using the Persistent Scatterer Interferometry (PSI) technique as well as analyzing the historical leveling data. The PSI technique is used to map the location of hazard zones and their ongoing subsidence rate. Two ascending and descending Sentinel-1 data sets, collected between Jan 2015 and May 2020, covering the Gävle city were processed and analyzed. In addition, a long record of a leveling dataset, covering the period from 1974 to 2019, was used to detect the rate of subsidence in some locations which were not reported before. Our PSI analysis reveals that the center of Gävle is relatively stable with minor deformation ranged between -2±0.5 mm/yr to +2±0.5 mm/yr in vertical and east-west components. However, the land surface toward the northeast of the city is relatively subsiding with a higher annual rate of up to -6±0.46 mm/yr. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposits map was overlaid with PSI results and it shows the subsidence areas are mostly located in zones where the subsurface layer is marked by artificial fill materials. The knowledge of the spatio-temporal extents of land surface subsidence for undergoing urban areas can help to develop and establish models to mitigate hazards associated with such land settlement.
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During the last twelve years, a long history of data has been acquired by the SAR sensors on board the ERS-1 and ERS-2 satellites offering a wide range of interferometric applications. With the launch of ENVISAT in 2002, the more advanced SAR (ASAR) has given continuity to the success of the remote sensing mission of the ERS satellites by ensuring and increasing the value of the archived ERS data. The subject of this study is to demonstrate the continuity of the interferometric measurements obtained from the combination of long temporal series of SAR differential interferograms in order to derive small subsidence displacements. 1.
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In the present study, we have investigated spatial-temporal behaviours of the land subsidence induced by reclamation activities in Macao Special Administrative Region, a coastal city of southern China. An advanced Synthetic Aperture Radar Interferometry (InSAR) technique, referred to as Interferometric Point Target Analysis (IPTA), was applied to retrieve the deformation rate and displacement time series during the period from July 2006 to March 2009. Validated by levelling survey measurements, the InSAR-derived results showed a fairly stable and homogeneous pattern within the land of Macao before 1912, which consists mainly of the three granitic islands of Macao Peninsula, Taipa Island and Coloane Island. In contrast, relatively large deformation rates (between − 15 and − 41 mm year) and local spatial settlement variability were discovered within the latest reclamation areas. A quantitative comparison analysis of the relationship between the observed settlements and the evolution of land reclamation indicated a time-dependent settlement behaviour with respect to the age of the reclamation. Another key result was that differential settlements were detected over short distances in reclamation areas, particularly between the ground surfaces and the adjacent buildings, thus providing valuable information not only for early detection and remedial activities of potential settlement of such buildings but also for the design of future facilities adjacent to the buildings, particularly for that of large infrastructure developments.
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Using new analysis techniques of space-based radar data, surface deformation features caused by various tectonic, geomorphic, and hydrologic processes are imaged in the San Francisco Bay area of California. Uplift is due mainly to sub-mm/yr tectonic upheaval related to slip along and interaction of the complex array of San Andreas transform system faults, while seasonally recharging aquifers account for tens-of-millimeters rise. Observed downward motions are caused by seasonally depleting aquifers, active deep-seated landslides, and rapid settling of unconsolidated sediments and man-made fill alongside the San Francisco Bay. Synthetic aperture radar interferometry (InSAR) from Earth-orbiting spacecraft has revolutionized the field of crustal deformation research since its first geophysical application, about a decade ago. During the last 10 years, InSAR has been used to study a wide range of surface displacements related to active faults, volcanoes, landslides, aquifers, oil fields and glaciers, to name just a few, at a spatial resolution of less than 100 m and centimeter-level precision [see Massonnet and Feigl, 1998; and Bürgmann et al., 2000a for reviews of the InSAR method and applications]. The temporal resolution is limited by the approximately monthly repeat time of satellite flyovers. Due to the viewing geometry of the radar satellite (the beam along which distance changes are measured is oriented at ~23° off vertical), InSAR is particularly sensitive to vertical deformation, but cannot detect displacements parallel to the orbit track. Severe limitations to the InSAR method remain, especially decorrelation of surface scatterers due to vegetation or other surface change processes, incoherence caused by large satellite orbit separations between the two image acquisitions used to make an interferogram, and noise from signal delays in the Earth's atmosphere.
Conference Paper
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Persistent Scatterer Interferometry (PSI) is a remote sensing technique to measure and monitor land deformation from a stack of interferometric SAR images. Its main products are the deformation maps (maps of the average displacement rates), the deformation time series and the maps of the so-called residual topographic errors. In this paper, we describe a new product derived from X-band PSI: the thermal deformation maps. This paper briefly describes the thermal component of the PSI phase observations and outlines the approach to estimate the thermal maps. The last part of the paper discusses three examples of thermal maps derived from a stack of 28 StripMap TerraSAR-X images that cover the metropolitan area of Barcelona (Spain).
Temporal and spatial resolution requirements for extracting urban/suburban infrastructure and socio-economic attributes from remote sensor data are presented. The goal is to relate the user information requirements with the current and proposed remote sensing systems to determine if there are substantive gaps in capability. Several remote sensing systems currently provide some of the desired urban/suburban infrastructure and socio-economic information when the required spatial resolution is poorer than 4 by 4 m and the temporal resolution is between 1 and 55 days (e.g., Landsat MSS and Thematic Mapper, SPOT1-4, Bussian TK-350, BADABSAT, Indian IRS-1CD, NOAA A VHBB, GOES, Meteosat). Current high spatial resolution sensor systems such as the Russian SPIN-2 KVR-1000 (2- by 2-m panchromatic; when in orbit) and proposed sensor systems (EOSAT Space Imaging IKONOS 1- by 1-m panchromatic; Earth Watch Quickbird 0.82 by 0.82 m; OrbView-3 1 by 1 m) may provide additional capability. Large-scale metric aerial photography or digital camera imagery with spatial resolutions ranging from ≤ 0.25 to 1 m will still be required to satisfy several important urban/suburban information requirements.
This paper presents an analysis of the performance of the Coherent Pixel Technique for urban subsidence monitoring using TerraSAR-X data. Repeated observations for the period comprised between July 2008 and September 2009 have been used. For this purpose the city of Murcia has been selected as a test-site because it is affected by subsidence due to groundwater exploitation. The obtained results are compared with those obtained from ERS/ENVISAT data belonging to the same period and validated with pre-existing information. Subsidence data reveal average rates of subsidence for the whole area up to − 5 mm/year with local values that reach − 35 mm/year. These results are analyzed with respect to the main factors that control subsidence mechanisms: the thickness of the compressible layer, the presence of pumping wells, and the water table variation. Finally a local analysis of several buildings and infrastructures is presented. Therefore the usefulness of X-band radar technology, not only to improve the knowledge of this kind of regional phenomenon, but also to study its effects on local areas such as buildings and infrastructures is demonstrated.
Persistent scatterer (PS) analysis of InSAR data has proven to be a very sensitive technique for measuring steady deformation in urban areas. Standard methods can also treat non-steady deformation if displacements follow a simple parametric function of time. Applying these methods to estimate deformation on volcanoes is, however, more challenging because a) the majority of volcanoes are not urbanized and therefore lack the man-made structures that are recognized by the PS algorithm, and b) deformation tends to proceed at an irregular rate. We present a new method for identifying PS pixels in a series of interferograms, based on a combination of their amplitude and phase characteristics, that is applicable to the study of natural targets. The phase-based method avoids one major problem with the existing algorithm: low amplitude pixels with actual phase stability are not identified. Our method also uses the spatial correlation of the phases rather than a specified phase history so that we can observe temporally-variable processes. The algorithm involves removing a residual topographic component of the phase for each PS, assumed proportional to the interferometric baseline, and then unwrapping the phase of the PS interferogram stack both temporally and spatially. Our technique finds scatterers with stable phase characteristics, even for pixels that do not contain man-made structures. It is applicable to areas where conventional InSAR fails due to complete decorrelation of the majority of scatterers, yet a few stable scatterers may be distributed amongst them. We created and analyzed a stack of 21 interferograms for Long Valley Caldera in California, and identified 23,000 PS pixels in the study region, as opposed to 300 found with Ferretti's (2001) algorithm. The resulting unwrapped phases, when transformed into estimates of line-of-sight displacements, agree with GPS, leveling and EDM measurements made over similar time intervals, validating the technique. Furthermore, the dense spatial coverage of the PS allows us to refine models of the sources of deformation within the caldera.
The Venice Lagoon in Italy is a unique environment vulnerable to loss in surface elevation relative to the mean sea level. We present detailed synthetic aperture radar (SAR) interferometric analyses on persistent point targets for the historical center of Venice, the tourist area of Sottomarina, and the Zennare farmland close to the southern lagoon edge. The selected areas are characterized by different degrees of development and our analyses show the remarkable capability of SAR Interferometric Point Target Analysis (IPTA) to map land displacement rates in densely urbanized zones and to detect movement information on isolated structures with a mm/year accuracy. A detailed analysis of the time series from 1992 to 2000 provided by IPTA shows that the vertical component of the measured displacements are the superposition of a short timescale, generally seasonal, movement on the order of 1 cm that is likely related to the fluctuation of environmental variables (temperature, piezometric head in the aquifer system underlying the lagoon, sea/lagoon water level) and a long-term ground deformation associated with building construction, the geomorphology of the area, and the human development of natural resources. If Venice is confirmed to be generally stable, significant long-term subsidence on the order of 4 mm/year is detected at the Sottomarina coastland. The highest displacement rates, of up to 8–10 mm/year, are recorded in the farmland bounding the lagoon margin where the movements are found to be highly site-specific.