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A NEW METHOD OF SIMULATION OF INTERFEROGRAM IMAGE FOR REPEAT- 
PASS SAR SYSTEM 
Jianmin Zhou a,b *, Zhen Li\ Xinwu Li a , Chou Xie a b 
a State Key Laboratory of Remote Sensing Science, Jointly Sponsored by the Institute of Remote 
Sensing Applications of Chinese Academy of Sciences and Beijing Normal University, Beijing, 100101-( zli@irsa.ac.cn, 
xinwuli@irsa.ac.cn, irsa_xiechou@yahoo.com.cn) 
b Graduate School of Chinese Academy of Science, Beijing, 100039-jmzhou@irsa.ac.cn 
Commission VII, WG VII/6 & VII/7 & II/l 
KEY WORDS: SAR, Interferometer, DEM, Orbit Data, Satellite, Geometry 
ABSTRACT: 
Interferometric synthetic aperture radar (InSAR) techniques are applied in many fields, ranging from digital elevation model (DEM) 
generation to surface motion monitoring and tomography. In InSAR processing, simulation of interferogram is a common practice. 
To enhance the understanding of the InSAR mapping process and to test new algorithms and validate the whole chain of InSAR 
processing from the interferogram creation to the DEM reconstruction, accurate tools for the simulation of the topographic InSAR 
phase are necessary. The simulation methods of interferogram, which have been mentioned in the literatures, are developed in very 
simplified imagery geometry model or have the assumptiom of parallel orbits and flat earth surface, the baseline of the whole scene 
is fixed. So these simulation methods haven’t been applied widely and more errors were introduced. This paper presents a new 
simulation method using external DEM, real radar sensor parameters and orbit data. This method avoid the limitations that were 
presented in the before literatures. 
1. INTRODUCTION 
Recently the application of InSAR technology becomes more 
and more wide. There are many open research topics in SAR 
inerferometry, varying from optimization of the processing 
algorithms to developing new applications of InSAR. InSAR 
technology is a new application of SAR in topographic 
mapping(Eineder M., 2003, R. F. Hanssen et al., 1999). During 
the research of SAR or InSAR, a simulator seems to be the most 
practical tool for of measuring algorithm, so different 
simulators are developed for selecting an optimum imagery 
mode of SAR, understanding the effects of illumination angle 
and the terrain relief on SAR images, testing and optimizing the 
interferometric SAR processing algorithms, or insight into radar 
received signal of given the terrain(L. S. Wary et al., 2000 Xu 
W.and Cumming B., 1997, Kun Ren et al., 2003, Wary L. S et 
al.,2000,). The simulation of interferogram, which have been 
mentioned in the literatures, are developed in very simplified 
imagery geometry model or have the assumptiom of parallel 
orbits, flat earth surface or hvae the fixed baseline of the whole 
scene. In this paper we develop an new interferogram simulator 
which works with external DEM, real radar sensor parameters 
and precise orbit data. This simulator work under the same 
coordinate system, that is the ground point and the satellite are 
converted to the same coordinate system, and the baseline 
between two satellite isn’t fixed and is determined by the 
satellite position automatically. This make the simulated SAR 
interferogram as realistic as possible. It is possible to avoid 
many errors. 
2. SIMULATION OF THE INTERFEROGRAM 
2.1 Rationale 
The geometry of an InSAR system is shown in Fig. 1, where O 
is the center of the Earth, the coordinates system is the Earth 
center Cartesian coordinates. A b A 2 express two satellites, and 
P is ground point(Zhong Lu, 2007, R. Bamler and P. Hard, 
1998). From the theory of SAR interferometry we know that the 
distance between the satellite and the ground point can be 
determined accurately by the phase information of the SAR 
image. Based on the observation, the phase difference of two 
SAR images is defined as interferogram (j) given by 
j. 4 x(ry-r 2 ) 
9 = (i) 
where r ( , r, are the distances between a target point P and 
satellite A { , A 2 , respectively, & are wavelength of radar. 
So we use the principle of equation (1) to simulate the 
interferogram, and this simulation depends on the accurate 
computation of the range difference between two satellite to the 
ground point. The arithmetic of our simulator include three 
parts: calculating the ground point coordinates, calculating the 
satellite position coordinates and using equation (1) to 
determine the interferogramic phase. 
* Jianmin Zhou(1978-), male, Ph.D Student, major in microwave remote sensing.