Full text: Mapping without the sun

X.M. Luo G.M. Huang Z. Zhao 
Chinese Academy of Surveying and Mapping, 16 Beitaiping Road, Beijing- 
romanl 121@hotmail.com, huang.guoman@163.com, zhangzhaochina@163.com 
KEY WORDS: Topographic Map, Element, Airborne SAR, Texture, Updating 
Currently the topographic map in scale of 1: 10000 is going to be updated in a lot of regions in China. SAR has unique advantage in 
map updating of those regions where are usually rainy and cloudy. At present the resolution of the airborne S.AR already reaches 
even over lm. With the improvement of the imaging technique, SAR has been ready for map updating in scale of 1: 10000. This 
article researches on updating the topographic map element by high resolution of airborne SAR. First the mechanism of the SAR 
imaging is analyzed, second SAR image is done some preprocessing (such as radiometric correction and geometric correction), the 
texture and feature of SAR image are researched on and what kind of topographic map element could be extracted by means of high 
resolution airborne SAR is test, finally it’s clear that high resolution airborne SAR could extract many kinds of topographic map 
element: airport, railway, road, river, lake, pool etc. This research makes the well technique foundation of using high resolution 
airborne SAR to update topographic map in scale of 1: 10000. 
Topographic map is the basic data for national departments and 
various projects, which could offer lots of information [Kang 
T.J. 2006]. With the fast development of economic construction 
and the rapid step of urbanization construction, the topographic 
environment changes with each passing day, especially the 
ground feature. But newly-built roads, aqueducts and the 
changes of various landuse status made speed of the 
topographic map updating slowly, so it is an important to carry 
on the revision of topographic map. 
Nowadays the topographic map by scales of 1: 10000 is going 
to be updated in many regions. Aerial photogrammetry is the 
traditional method for updating topographic map by middle and 
small scale, but the speed of data obtains is slow, the cost of 
photogrammetry is high, even in parts of this place, just as 
Yunnan province, Guizhou province, Sichuan province, where 
the weather is not well, usually rainy and cloudy, the optical 
image couldn’t obtain. With the technology of remote sensing 
developed rapidly, there is a kind of new method for mapping 
and updating the topographic map. SAR as a top observation 
technology which appeared in 20 century, could acquire the 
image in day and night, and look through clouds, smoke and 
fog, even penetrate ground material. Now the resolution of the 
airborne SAR image could be close to optical image’s 
resolution, as a result, using high resolution airborne SAR 
images to update topographic map elements is possible. 2 
so on. Due to receive the echo, antenna of SAR needs to 
side-glance, in this way, the area where SAR could image is 
larger than photogrammetric area. So it would cost less than 
traditional method. In a word, it’s a suitable method for 
updating topographic map by using high resolution of airborne 
Image data is the most important part of the whole updating 
task. The SAR image process is nearly the same with the 
remote sensing image process. The image process includes the 
follow steps: data import, speckle suppression, radiometric 
correction, ortho- rectification, texture analysis[Zhao. Z. 2004]. 
After the basic image process, SAR image is changed to DOM 
as the prepared data. Then 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. 
The mechanism of the SAR imaging is different from the 
optical imaging. The optical image is obtained by 
photographing and scanning of optical sensor, which is passive 
to receive the reflected electromagnetic wave from the ground 
material. However, as an active system, SAR could transmit 
and also receive the microwaves. After the microwaves interact 
with ground material, SAR image records the scattered 
microwaves from ground material, and could invert the 
physical characteristic of ground material, like: target shape, 
material, surface roughness, surface electrical properties, and

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