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SUBSIDENCE MEASUREMENT WITH PS-INSAR TECHNIQUES
IN SHANGHAI URBAN
Lijun Lu Mingsheng Liao
State Key Laboratory for Information Engineering in Survey, Mapping and Remote Sensing,Wuhan University Luoyu
Road 129, Wuhan,P.R.China,430079,lulijun@lmars.whu.edu.cn
Commission VII, WG VII/2
KEY WORDS: DInSAR, PS-InSAR, Subsidence, Measurement, Urban
ABSTRACT:
Spacebome SAR Differential interferometry (DInSAR) has been used to monitor some geological disasters such as ground
subsidence. This paper applies two Permanent Scatterer InSAR(PS-InSAR) techniques to measure long-term and short-term
subsidence in urban area of Shanghai urban. A great number of archieved ERS data are utilized to measure long-term subsidence
during 1993-2000 year. A small set of ASAR data are utilized to measure short-term subsidence during 2003-2005 year. The
subsidence measurement results are examined with simultaneous leveling during the two periods, and comparison result shows a
good agreement. Furthermore, the causes of subsidence are qualitatively analyzed in the main subsidence regions of Shanghai urban,
and the variation of subsidence in two different periods can be detected according to the obtained subsidence measurement results.
1. INTRODUCTION
The surface deformations monitoring using DInSAR technique
has shown some good results in the last years of research. As
the extension of DInSAR technique, PS-InSAR technique has
been recognized as a powerful tool for large-scale and long
term monitoring small surface deformations in urban areas (Li,
Liao et al., 2004). The strategies of PS technique is to find
point-wise permanent scatters (hereafter called PSs) that exhibit
phase stability over a long period of time, estimate and remove
atmospheric phase contribution, DEM error and system/thermal
noise etc., and finally measure precise displacement on
permanent scatters. The advantage of PS-InSAR technique lies
in that it can practically overcome the problems of geometrical
and temporal decorrelation existing in DInSAR by using a large
amount of SAR data.
In this paper, PS-InSAR techniques are applied to the
subsidence measurement in Shanghai urban as Shanghai urban
has been suffering the subsidence disaster since 1920s. Aiming
to the different survey applications, this author utilized the two
PS-InSAR techniques on two different amount of SAR dataset.
In the first study, the long-term subsidence can be measured by
applying traditional PS-InSAR technique—Permanent Scatterer
(Ferretti et al., 2000; 2001), as an amount of ERS-1/2 archived
images from 1993 to 2000 in Shanghai urban are available from
ESA. In the second study, the short-term subsidence from 2003
to 2005 in Shanghai urban can be measured. As the extension of
ERS-1/2 satellite, ENVISAT satellite has just in operation for
several years, only small ASAR dataset are acquired so that it is
insufficient to make an analysis in long time series. Considering
limitation in the data availiability, another PS-InSAR technique
— Spatio-Tempral Unwrapping Network (STUN) (Bert M.
Kampers, 2006) can be applied. The STUN technique is
improved in this paper for subsidence measurement in small
dataset.
Since Shanghai government has been made continuous leveling
since 1990s, it provides us a good validation standard for
precise evaluation of subsidence results by two PS-InSAR
techniques. The subsidence results are validated by comparing
the corresponding PSs and Leveling Benchmarks (LBs). On the
basis of results validation, the causes of subsidence are
qualitatively analyzed in the main subsidence regions of
Shanghai urban, and the variation of subsidence in two different
periods also can be detected according to the achieved
subsidence results.
2. DESCRIPTION OF TEST AREA AND DATA SET
2.1 Test area
Shanghai is the largest industrial city in China, standing on the
East China Sea and situated at the front edge of Yangtze Delta,
as showed in the left pictures of figure. 1. Subsidence due to
underground water over-pumped has become a major problem
in the city since 1920s. In the recent decade, with the increasing
land use for urban development, the subsidence disaster has
become worse. The severe subsidence generally occurred in the
urban areas of Shanghai where the sites of underground water
extraction and major municipal engineering constructions are
located. Therefore we lay emphasis study on the urban of
Shanghai, as shown by the right picture in figure. 1.
Figure. 1 The location of Shanghai city. The left picture shows
the location of Shanghai city in China, the right picture shows
the location of test area, i.e. urban of Shanghai, covering an
area about 1000 km 2 .