Monitoring Land Subsidence in the Tokyo
Region with SAR Interferometric Stacking
Techniques
191
Paolo Pasquali, Alessio Cantone, Paolo Riccardi, Marco De Filippi,
Fumitaka Ogushi, Masayuki Tamura, and Stefano Gagliano
191.1
Introduction
Interferometric stacking techniques emerged in the last
decade as methods to obtain very precise measurements of
terrain displacements, and especially of subsidence phenomena. In particular, the so-called Persistent Scatterers
(Ferretti et al. 2001) and Small BASeline (Berardino et al.
2002) methods can be considered as the two most representative stacking approaches.
In both cases, the exploitation of 20 or more satellite
Synthetic Aperture Radar (SAR) acquisitions obtained from
the same satellite sensor with similar geometries on the
interest area allows to measure displacements with an
accuracy in the order of a few mm/year, and to derive the full
location history of “good” pixels with an accuracy of 1 cm or
better for every available date.
This paper is presenting results obtained with the two
techniques over an area in Japan characterized by significant
land subsidence, validating their accuracy in a quantitative
way and providing a geological explanation of the phenomena underlying this process.
191.2
Study Area
The area of interest of this study is the city of Urayasu
(Japan), part of the Chiba Prefecture and located in the east
of the city of Tokyo.
P. Pasquali (&) A. Cantone P. Riccardi M. De Filippi
Sarmap s.a., Cascine di Barico, 6989, Purasca, Switzerland
e-mail: paolo.pasquali@sarmap.ch
F. Ogushi
Exelis Visual Information Solutions K.K., Tokyo, Japan
M. Tamura
Department of Civil and Earth Resouces Engineering, Kyoto
University, Kyoto, Japan
A big part of the city of Urayasu, including the area
where Tokyo Disneyland has been built, is reclaimed land.
Figure 191.1. shows the historical evolution of the landfills,
while Fig. 191.2 shows the geographic location of the city.
191.3
Methods
The PS and SBAS approaches designed two algorithms that
focus each on a different type of objects and land cover to
favour in the analysis: the PS technique focuses on so-called
Point Targets, i.e. objects possibly of small size and with a
very well characterized geometry like corner reflectors (e.g.
buildings, rocks) and with a high temporal stability of the
backscattered signal; the SBAS technique vice versa is
concentrating the analysis on so-called distributed targets,
like open fields and not very geometrically characterized
objects.
Both approaches have been tested on the area of interest,
to analyse their suitability to monitor terrain subsidence and
to perform a relative assessment of the accuracy of the
obtained measurements. Two independent series of 26 and
respectively 35 SAR acquisitions have been processed, one
obtained from the ALOS PALSAR and one from the ENVISAT ASAR sensors, having different (L-band resp. Cband) central frequency.
All results shown in this paper have been generated with
the SARscape® software package.
191.4
Experimental Results
The average displacement rate in the period 2006–2010 in
the Urayasu region, as obtained through PS and SBAS
processing of ASAR and PALSAR data is shown in
Fig. 191.3.
S. Gagliano
Exelis Visual Information Solutions Italia, Concorezzo, Italy
G. Lollino et al. (eds.), Engineering Geology for Society and Territory – Volume 5,
DOI: 10.1007/978-3-319-09048-1_191, © Springer International Publishing Switzerland 2015
995
996
P. Pasquali et al.
Fig. 191.1 Landfill area around
Urayasu (Japan) in years 1950,
1975, 1980 from left to right
(Urayasu City Government
Homepage 2013)
Fig. 191.2 Location of Urayasu
City
The coverage obtained with the two methods from different data is in this urban area very similar. As expected, the
SBAS data show smoother results, while the spatial resolution obtained in the PS case is better and many spatial details
are more accurately preserved; PALSAR data show higher
spatial variability, while ASAR data provide higher accuracy. Nevertheless, all 4 approaches provide very consistent
results, able to well delineate the same areas of terrain
compaction at the borders of different land-fills.
A quantitative validation of the results is summarised in
Fig. 191.4, where both relative (SAR-SAR) and absolute
(SAR-GNSS) statistics confirm the very high accuracy of the
results, that can be synthetically estimated in the order of
magnitude of 1 mm /year.
Figure 191.5 is showing a map of the depth of the upper
surface of the solid geological stratum, obtained from
independent ground measurements (The Japanese Geotechnical Society 2012).
191
Monitoring Land Subsidence in the Tokyo Region with SAR
Fig. 191.3 Average
displacement rate in the 2006–
2010 period in the area of
Urayasu, as obtained from
PALSAR (above) and ASAR
(below) data through SBAS (on
the left) and PS (on the right)
processing. Colour scale is
between −15 (subsidence) to +5
(uplift) mm /year
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P. Pasquali et al.
Fig. 191.4 Relative validation of SBAS ASAR and PALSAR (upper left), PALSAR PS and SBAS (lower left), ASAR PS and SBAS (lower
right) and absolute validation of ASAR SBAS against GNSS data (Miyazaki et al. 1998)
Fig. 191.5 Depth of the upper surface of the solid geological stratum (Pleistocene sand stratum with the standard penetration test N value > 50) in
Urayasu city (The Japanese Geotechnical Society 2012)
191
Monitoring Land Subsidence in the Tokyo Region with SAR
999
Fig. 191.6 Average displacement rate in the 2006–2010 period in the Haneda Airport area, as obtained from ASAR data through SBAS
processing (on the left) and corresponding optical image (on the right)
It is interesting to notice how precisely the areas undergoing large subsidence correspond to those having thick
layers of soft soil over stiff basement. This provides an
additional, independent validation of the interferometric
stacking results, offering a geological explanation of the
mechanisms of terrain compaction that are at the origin of
the measured subsidence.
Figure 191.6 show for example the average displacement
rate measured over the Haneda airport, where significant
subsidence can be identified in the area between the terminal
2 and the C runaway. The mechanisms at its origin shall now
be investigated.
191.5
Berardino P, Fornaro G, Lanari R, Sansosti E (2002) A new algorithm
for surface deformation monitoring based on small baseline
differential SAR interferograms. IEEE Trans Geosci Remote Sens
40:2375–2383
Ferretti A, Prati C, Rocca F (2001) Permanent scatterers in SAR
interferometry. IEEE Trans Geosci Remote Sens 39:8–20
Miyazaki S, Hatanaka Y, Sagiya T, Tada T (1998) The nationwide GPS
array as an earth observation system. Bull Geographys Surv Inst
44:11–22
Urayasu City Government Homepage (2013) http://www.city.urayasu.
chiba.jp/. Accessed 25 Sept 2013
The Japanese Geotechnical Society (2012) Japan society of civil
engineering, and architectural institute of Japan, Report of the
Urayasu city review and research committee on liquefaction
countermeasure techniques
Conclusions and Outlook
The results shown in this paper provide a new validation of
the accuracy obtainable with the PS and SBAS techniques,
and of their suitability for measuring and monitoring small
terrain displacements due to subsidence phenomena.
If then, from the application point of view, the mechanisms at the origin of the displacements measured over the
Urayasu area have been fully understood, further research
shall be invested to comprehend similar phenomena that
have been obtained from the same data and techniques in
neighbouring areas.
References