Yong Ge
object. It is capable of grasping the difference of images produced with different parameters(incident
angle wavelength and polarimetric ways ) under complex conditions. This predictability can help the integrated
system to choose optimal system parameters (Shu, 1997). But SAR simulated image produced by this method is
not a real SAR image, but is a pseudo SAR image.
4. 2 The Method of Simulating Coherent Video Signal
The definition of the method of simulating coherent video signal is to recur coherent video signal including
amplitude and phase realistically, and recur the complete process of this signal from transmitting to receive via
atmospheric propagation and being scattered by ground object.
The differences from the former method are as follows. First, the full process of simulating image is based on
the propagation function of SAR imaging system. Next, the back scattering coefficient is calculated by the
interactive model between SAR coherent signal and ground object and not calculated by the coincidence relation
of ground cells material texture database and back scattering database. Last, as result of the system based on
propagation function, so we can test the capability change of SAR electronic component, and optimize the design
of SAR system. In Virtual SAR system, we have adopted this method.
Here, we give an example about simulation of point object and multi-point object. The flight
platform can determine the phase center coordinates of antenna A(X,Y,Z) for each phase. Here, X
axis signifies flight direction of flight platform corresponding to ground object when ground object
lies in the center of wave beam. Z signifies the direction perpendicular to ground surface. We
assume the position of transmitting antenna as Al and the position of receiver antenna as A2. C
signifies light speed. The each delay is calculated as follows:
t, -(P- Ai|-|P - A2])/C 1
So we can get the formula below.
Sr(t) = Sx(t—t,) 2
Where Sr(t) is echo signal of antenna; Sx(t) is transmitting signal of antenna.
As for multi-point object, we can first simulate each point and multiply itself ground reflection
coefficient R1, R2...Rn . After we calculate echo signal of each point, we add all of echo signal of
point and then we can get echo signal of multi-point object. The formula of simulating ground
object in time domain is below:
Sr) =R12Sx(t 1, V+ R22 8x1 ~1 + .. A Rn 2 Sx (1 ~1,) 3
Comparing the former method, it needs to do a great deal of calculation for gaining the distribution of
scattered field of object. So it is complicated and time-consuming. But we can research the detection and
identification of object in relation to its geometry further using the method.
5 CONCLUSION AND PROSPECT
In this paper, we put forward the conception of Virtual 3D SAR integrated system and expound the advantages of
Virtual 3D SAR system. Then we display some functions of this system. Though some of research works are in
the preliminary stage in the whole framework , we trust that the 3D virtual SAR system will be able to bring about
great change to remote sensing technology.
At the same time, here we should realize definitely that due to the complication, diversity and variation of natural
world, it also means that the task of computer simulation SAR system is time-consuming and very hard.
ACKNOWLEDGMENTS
KZ 95T 03-04
This work is supported in part by Chinese Academy of Sciences Project Fund coded 7051 81-703 ANd in part by
National Natural Science Fund Committee Project coded 69896250.
REFERENCES
Asrar, G., et al, A 3-D RT method for optical remote sensing of vegetation land surface, Proceeding 3" Intern.
Colloq. Physical measurement and signature in remote sensing, Courchevel, France, pp361-367, 1991.
126 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.
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