Research on the Framework of Computer 3D Simulation SAR Integrated System

5 The framework of computer 3D simulation SAR integrated system

5.1 Basic approach of realizing the simulation SAR integrated system
The basic approaches for realizing the computer 3D simulation SAR system are concluded as follows:

Establishing the error propagation model. In this paper, it is mentioned in section 2 that computer can be used to simulate the ground objects and directly make inversion. But due to the complexity and variety of ground objects, this method need further research yet. At the present time, the usual method of inversion is based upon the images of remote sensing.

As we know that owing to the limitation of equipment and processing technology, the error of SAR image obtained is relatively great, which bring many difficulties to research on the remote sensing mechanism. So, for gaining the right inversion parameters, the first step should lay on researching on the error propagation model of SAR image from the mechanism of SAR setting out, analyzing on various errors sources effecting real SAR image. We use these sources to correct the corrupted radar image. Based on the correct image, the further research should be performed on the relationship between the gray value of radar image and the scattering characteristic of ground objects. So to establish error propagation model is a rudimental work for realizing the computer simulation SAR integrated system.
Establishing the inverse model for ground objects. On the basis of large amount of the correct remote sensing images and the scattering mechanism of ground objects in various conditions obtained through field work or computer simulation method as an assistant tool (in section 2), the inverse model can be set up.
Establishing the mechanism model describing vegetation growth and ground object variation.
Establishing the SAR imaging model. It is difficult to simulate and set up signal propagation model to form coherent image under sensor flight status.
Setting up the 3D simulation SAR system. This simulation SAR system will integrate these models mentioned above into one, and meanwhile harmonize the relationship among them.
Model training. We select M training areas and simulate them using the 3Dsimulation system by means of the material of training areas (DEM or land use map which mainly provide with the rough distribution information of landform or vegetation). The simplest method to test model fidelity is to examine by eyes (Lin, 1999). At the same time, it can combine with field experiment and high-resolution images to adjust the simulation models until the error between the simulation image and the theoretic images is satisfying. When the train is finished, we can use the 3D model of SAR system for producing SAR simulation image. Figure 1 shows the flow chart of realizing the 3D computer simulation SAR system.

Figure 1 Approach of Realizing The Computer Simulation SAR Integrated System
5.2 Integrated framework for computer 3D simulation SAR system
The integrated system consists of five parts: SAR simulation imaging system; vegetation and ground object simulating system; image processing and information retrieval; application model; 3D language environment. The application for simulation SAR system using computer has been mentioned in Introduction. Besides these applications, it also includes flood prediction, military reconnaissance and battlefield simulation. The 3D language environment is a kind of expression of simulating SAR system, and it can strengthen the visual effect .analyze and embody the work behaves and effects of the 3D simulation SAR system in different conditions from multi-angles. Figure 2 shows the framework of Computer 3D Simulation Integrated System.

Figure 2 The Framework of Computer 3D Simulation Integrated System
The simulation SAR system has some characteristics as follows:
1) SAR imaging system simulates SAR to transmit and receive wave and form image. Considering the relations among themselves and the error effects, we can establish the signal transmitting equation. Adjusting the imaging parameters and the attitude of aircraft, we can gain different images which can be able to serve for different applications. Of additional interest here is that the imaging system can even provide images with different precision. During designing the real SAR system, due to the design problem or high price of hardware, perhaps we can not obtain high-resolution SAR images. However, only if we get the corresponding algorithm in the simulation SAR system, we can obtain the high-resolution simulation images.

2) Using structure real model, on the one hand it can simulate realistic structure of vegetation and ground objects, on the other hand it can calculate the signal echo through simulating the interaction between microwave and vegetation and ground objects. This simulating system can not only produce the SAR simulation image at the same area and at different time, but also produce the SAR simulation image at different areas and at the same time.

3) Characteristics of radar image produced by the simulating system are as follows:
i.Besides the model error, the simulation images which use ideal algorithm model don't contain these errors derived from outside factor disturbance.
ii.The radar image is not a simple COPY for the simulating ground object or vegetation but the expression of physical mechanism of interesting areas. So we can dig out much more knowledge from the image.
iii. It can be able to be fused with other data sources.

6 Conclusion and prospect
In this paper, we review the research situation of computer simulation and the work mechanism of real SAR system, discuss the integrated framework for computer 3D simulating SAR system, put forward the preliminary conception of integrated system and expound the advantages of 3D simulation using computer. Though some of research works are in the preliminary stage in the whole framework yet, we trust that the 3D simulating 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
This work is supported in part by Chinese Academy of Sciences Project Fund coded KZ95T-03- 04-04.Kjg51-B1-703 and in part by National Natural Science Fund Committee Project coded 69896250-4. The author would like to appreciate Prof. Zhou chenhu.Prof. Xiang yueqian.Dr. Du yunyan and Dr. Chen lijun for their help in the preparation of this manuscript.

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