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Mapping without the sun
Zhang, Jixian

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