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URBAN MONITORING USING PERSISTENT SCATTERER INSAR AND 
PHOTOGRAMMETRY 
Junghum Yu*, Alex Hay-Man Ng, Sungheuk Jung, Linlin Ge, and Chris Rizos. 
School of Surveying and Spatial Information Systems, University of New South Wales, Australia. 
jung.yu@student.unsw.edu.au 
KEY WORDS: Persistent Scatterer, InSAR, Urban Monitoring 
ABSTRACT: 
The purpose of this paper is to monitor deformation due to groundwater extraction in urban area using Persistent Scatterer InSAR 
(PSInSAR) and Photogrammetry. Theoretically, PSInSAR technique allows for millimetre precision ground deformation mapping 
based on the utilization of long period of interferometric SAR data. One main advantage of PSInSAR method, compared to 
conventional deformation surveying methods such as levelling and Global Positioning System (GPS), is the coverage of large area. 
However, PSInSAR method has difficulty in explanation of each single object or detail information of small objects because of 
current space-bome radar imagery which has approximately 25m spatial resolution. In order to solve this problem, we used aerial 
photogrammetry method to survey detail information of objects in selected area identified by PSInSAR. 
1. INTRODUCTION 
Nowadays, continuous monitoring of urban area represents one 
of the most interesting and major subjects of research in remote 
sensing whenever a Synthetic Aperture Radar (SAR) instrument 
is used. Typically, the aerial photogrammetry and Light 
Detection and Ranging (LiDAR) methods which have high 
spatial resolution were used for urban monitoring. Major cities 
have rapidly changed and extended during last century and over 
50 percentage of the population now live in towns and cities. 
Much population who lives exists in the city consuming huge 
amount of water everyday. Water supply is main element of city 
life maintaining. Surface water and groundwater are two major 
water sources in Australia. Water shortage is one of the major 
social and economic environmental problems in Australia. 
Australia is the driest inhabited continent on Earth, with highly 
variable rainfall patterns. The amount of water usage has 
increased dramatically in Australia which leads to significant 
increase in demand for groundwater resources due to the limit 
amount of surface water supplies available. Normally, there are 
two surveying methods used for ground deformation monitoring 
which include the Levelling and Global Positioning System. 
However, it is very difficult to cover the large area and set up 
bench marks for the ground survey. Therefore, Persistent 
Scatterer Radar Interferometry is used as a complementary 
method to conventional surveying method. Theoretically, the 
Differential Interferometry Radar (DInSAR) has the potential to 
precisely observe the ground deformation along the Line-of- 
Sight (LOS) direction up to a few millimetres. However, there 
are four main problems, including (1) atmospheric disturbances 
causing noise from signal delays, (2) temporal decorrelation of 
surface scatterers due to seasonal vegetation and/or other 
surface change, (3) geometrical decorrelation due to large 
baseline between two images acquisition result in incoherence 
and (4) ambiguity, have limited this technique to achieve its full 
operational capability. PSInSAR technique allows for 
millimetre precision ground deformation mapping based on the 
utilization of long time series of interferometric SAR data and 
huge area covering. However, current space-bome radar 
imagery which have approximately 25m spatial resolution are 
difficult to support the PSInSAR for detection of each building 
or detail information of small objects [Ge et al, 2001; National 
land, 2000; Ng et al. 2007]. 
2. PERSISTENT SCATTER TECHNIQUE 
Space-bome radar interferometry has already proven its 
potential for ground deformation monitoring application, for 
example, mining, earthquake and volcano studies, due to its 
high precision and spatial resolution [Colesanti et al, 2003]. 
Theoretically, the space-bome radar interferometry has the 
potential to precisely observe the ground displacement along the 
LOS direction up to a few millimeters. There are four main 
problems stated in previous section limited the conventional 
DInSAR technique from achieving its full operational capability. 
There four main problems are (1) atmospheric disturbances, (2) 
temporal decorrelation, (3) geometrical decorrelation, and (4) 
ambiguity problems. In the conventional DInSAR process, these 
problems may not be identifiable in the interferograms which 
have many noises. In PSInSAR process, however, the elevation 
and linear velocity rate corresponding to these problems can be 
estimated, as well as the atmospheric disturbances [Ferretti et al. 
2000, 2001]. The PSInSAR method first identifies all the PS 
points and a 2D deformation analysis is then applied to these 
points. Millimeter deformations can be achieved with this 
method which is more precise than the conventional method. 
The Persistent Scatterer (PS) technique is recent development in 
radar interferometric processing, which offers a practical way to 
reduce the main errors in conventional DInSAR processing 
method; temporal and geometrical decorrelation, and 
atmospheric artefacts. Atmospheric phase contributions are 
spatially correlated within a single SAR scene, but tend to be 
uncorrelated on time scales of days to weeks. Thus, atmospheric 
effects can be estimated and removed by combining data from 
long time series of SAR images, averaging out the temporal 
fluctuations. Radar scatterers that are affected by temporal and 
geometrical decorrelation are used, allowing exploitation of all 
available images regardless of imaging geometry. In a radar 
image, the reflected wave from a resolution element is the 
coherent sum of individual wavelets scattered by many discrete 
scatterers. Positive and negative interference of these waves 
takes increase to variation in the phase and amplitude of the