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Figl. Flowchart 
3.1 Speckle Suppression 
Because the special mechanism of the SAR imaging, there is 
speckle noise in the SAR image, which limit radiant resolution, 
and make it difficult to interpret the ground material, so it is a 
big problem to use the image data. Before other process, the 
first step is to suppress the speckle. The commercial software 
ERDAS Imagine is used to filter the speckle out from the SAR 
image in this research. Compared with various kinds of filter 
method, Lee-Sigma filter is better than other filters in speckle 
suppression. 
3.2Radiometric Correction 
The SAR image radiometric correction includes two steps: 
(1) Amplitude image data transforms from 32 bit to 8 bit. 
This transform could lead the data compression, so as to 
increase the speed of process and display. 
Fig. 2. Radar image presentation, the geometric connection of 
the range image and ground image. 
The transform formula: 
R s =R g x cos (1) 
or 
R g =^R^-H 2 (2) 
Where R g = the ground range 
R s =the slant range 
H=the aircraft altitude 
P = the depression angle 
The next step is to do the geometric correction. The traditional 
method is to use two order polynomials which assist with 
ground control point. It is mostly fit the smooth place. At the 
base of the geometric correction, using the DEM to do the 
Ortho- rectifications. After these steps, the DOM is generation. 
Finally mosaic the corrected image by ways of image 
coordinate in order to match the topographic map. 
3.4 Overlay the DOM and DLG 
The last step is to overlay of the SAR image to the DLG, 
manually generation of the changes of the polygons and lines. 
Overlay of the “changes” layer with the map’s layers, creation 
of the new updated layer. 
(2) Histogram statistic in order to make the output of 
dynamic area wide. For the sake of improving the 
definition of the image and ensuring the target 
information not losing, it is necessary to stretch the 
output of dynamic area. The ordinary way is to do liner 
stretching on the image, so as to display the detail of the 
image. 
3.3 Ortho- rectifications 
After the above process, it needs to do the Ortho- rectifications 
to the SAR image. First transform range image to ground range 
image. Because of the side imaging, the other special feature of 
the SAR image is that the original data image is the range 
image. The ground material of near-range is compressed, and 
the ground material of far-range is stretched [Shu.N, 2003]. So 
it is necessary to do this transform. 
4. RESULT 
In this research, the test SAR images are,- from Sichuan 
province. The resolution of SAR image is lm. Target texture is 
clear in the AIRSAR data, and hierarchical information is 
abundant. Through the test, some kinds of topographic map 
elements could extract from the SAR image [Rignot.E, 2003]. 
4.1 Water System 
The water system can classified into two kinds by its shape: the 
linetype water system, like river and canal; the non-linetype 
water system, like lake and pool. 
(1) the linetype water system update: the colors of water and 
bank displaying in the image are different, so it’s easy to 
determine the position of water edge and find the 
changes of the place.