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Mapping without the sun
Zhang, Jixian

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
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)
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
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.
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.