STUDY ON RADAR DIFFERENTIAL INTERFEROMETRY TECHNOLOGY 
AND IT’S APPLICATION TO MANI EARTHQUAKE USING ERS-1/2 SAR DATA: 
A CASE STUDY IN CHINA 
Qulin Tan **, Siwen Bi * Bin Wang *, Songlin Yang * 
? School of Civil Engineering & Architecture, Beijing Jiaotong University, Beijing, 100044, China - qulintan@sina.com 
? Institute of Remote Sensing Applications, CAS, Beijing, 100101, China — bisw(@irsa.irsa.ac.cn 
KEY WORDS: SAR, Earthquakes, Recognition, Mapping, Measurement, Change Detection 
ABSTRACT: 
Mani Earthquake, occurred on Nov. 8, 1997 in Tibet, China, is the strongest event in China since 90's in 20 century. Investigation 
and research of its principle and geometry, dynamics related to surface rupture zone is very significant to analyze the development 
and evolution of China's earthquake in the future. In this study, we investigate the distribution of surface deformation and extract 
displacement information of the earthquake rupture zone using differential SAR (ERS1/2 SAR) interferometry. The data set related 
to our study area are ERS1/2 SLC SAR images (April 15, April 16, 1996 ERS-1 and Dec. 2, 1997 ERS-2) provided by European 
Space Agency. We analyzed factors related to the surface deformation detecting: interferogram along the Margaichace-Ruolacuo 
fault under the special regional environmental conditions. From the changing interferogram, we concluded that the zone around 
Margaichace-Ruolacuo fault is the most severely deformed and the most possibly rupturing area; epicenter is located in this zone. 
Also we concluded from analyzing the fringe patterns that left-lateral shear movement is the whole deforming mechanism, 
furthermore, the offsets are also quantitatively estimated. We inferred that the horizontal offset displacement for the southern side at 
least reaches 2.8m and 1.75m at least for the northern side of the fault. All these results agree well with the slip measured in the field, 
  
with the displacement measured by surveying, and with the results of an elastic dislocation model. 
1. INTRODUCTION 
Radar differential interferometry is an up-to-date measurement 
technology. It is now possible to detect subtle changes in the 
Earth’s surfaces over periods of days to years with a scale 
(global), accuracy (millimeters), and reliability (day or night, all 
weather) that are unprecedented. The basic principle of the 
technique involves interferometric phase comparison of a series 
of SAR images. To date many examples illustrate how SAR 
differential interferometry can be applied to the study of 
coseismic deformation generated by an earthquake (Gabriel A. 
K, Goldstein R. M. and Zebker H. A. 1989; Gens R, Genderen 
V. J. 1996). Because of its unique capability, which no other 
technique provides high-spatial-resolution maps of earthquake 
deformation, these pioneering studies have generated enormous 
interest in the Earth science community because they point to 
an entirely new way to study the surface of the Earth. 
Although the techniques are now well documented in the 
international literature, only an example of acquisition of high 
accuracy DEM using SIR-C interferometric data has been 
reported in China (Wang Chao, 1997). For short of 
interferometric data source, the application examples of SAR 
interferometry is few as a whole in China, and the case study of 
differential SAR interferometry for mapping surface 
deformation is further much less. Along with the development 
of radar remote sensing, more and more SAR interferometric 
data would be available and China will certainly receive its own 
independent interferometric data source in the future. So it has 
become increasingly important to understand the limitations of 
the processing and the acquisition method itself for Chinese 
geoscientists. 
  
" Corresponding author. 
On the other hand, many Chinese geologic scientists are 
unfamiliar with SAR interferometry and its potential new 
applications, and its technical limitations need to be more fully 
explored. In an attempt to understand the principle and the 
influencing factors involved with repeat-pass space-borne SAR 
systems, such as the European Space Agency's ERS-1/2, 1 
examined an area around Mani, a region in Tibet, China using 
SAR differential interferometry. In this paper, ! will provide a 
brief description of the principle and processing steps, discuss 
the influencing parameters related to topography, and present 
the resultant changing interferogram calculated from the ERS- 
1/2 data. These are objectives of the study. 
2. PRINCIPLE OF SAR DIFFERENTIAL 
INTERFEROMETRY 
The development of differential SAR interferometry is based on 
SAR interferometry technique, and the interferometric data can 
be acquired by two antennae on the same platform, or by one 
antenna on "repeating" its orbit (Rodriguez E. 1992), and J. M. 
Martin. Because all space-borne SARs in run are single-band 
and single-antenna systems, many published literatures related 
to the technique have been used repeat-pass interferometric data. 
If ignoring some parameters influencing the quality of SAR 
interferometric data, such as atmospheric differences at the two 
times of imaging, internal clock drift, weather conditions, 
system noise et al, we present the interferometer geometry and 
range difference attributable to three factors: 1) A spherical 
earth with no topography, 2) topography, and 3) surface 
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