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Mapping without the sun
Zhang, Jixian

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
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.
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.
2.1 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.