The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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earth observation methods is low cost, accessibility for large 
area deformation mapping. 
(D) TimefYearl 
Fig. 4: LOS displacement time series for the point A, B, C, D 
5. CONCLUSIONS 
This paper is focused on the investigation of the surface 
deformation of the city Nanjing, the over all analysis is based 
on the exploration of the SBAS-DInSAR approach with a prior 
deformation knowledge applied to a SAR data set acquired by 
the ERS-2 sensor during 1996-2000 time interval. 
This study demonstrates the capability of the SBAS-DInSAR 
procedure to investigate the space-time characteristics of the 
deformation affecting the overall area. Moreover, we assume a 
cubic behaviour for the time variation of the deformation phase 
signal as a prior knowledge for the investigated area, and solve 
the equation in an optimal LS method directly, which simplify 
the SBAS-DInSAR algorithm. In particular, 13 interferograms 
in two subsets were generated using 8 ERS-2 SAR images 
acquired from August 1996 to April 2000 in Nanjing area, 
based on the cubic behaviour for the time variation of the 
deformation phase signal as prior knowledge, deformation map 
and displacement time series were generated using these 13 
interferograms and the implemented SBAS-DInSAR algorithm. 
Moreover, we find that the main deformation area is along the 
Yangtze River and to the west of the Qinhuai River, the 
maximum subsidence is around 12.0cm. finally, although the 
SAR images used in this study is relatively few, the 
deformation trend in the whole city has a good agreement with 
the conventional Leveling measurement, but more SAR images 
should be used to get temporal behaviour of the deformation 
maps of the area, more sophisticate algorithm for detecting 
local deformations on a small spatial scale should be developed. 
As an additional remark, the No. 1 north-south subway in 
Nanjing began in operation since September 2005. With a 
length of 21.72 km and 16 stations, Construction of the east- 
west No.2 subway with a length of 25.15 km is also in progress, 
developing new algorithm of InSAR technique to detect 
deformation along the subways is meaningful and challenge for 
the future. 
ACKNOWLEDGEMENTS 
The work is supported by Nature Science Foundation of China 
(No. 50579013).The precise ERS-2 satellite orbit state vectors 
have been provided by the Technical University of Delft. We 
thank the European Space Agency (ESA) which provides the 
ERS SAR data relevant to the city Nanjing. The authors would 
also like to express a special thank to Dr. Luo Haibin and Dr. 
He min for helps. 
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