against all the 
clusters in the 
School of Remote Sensing and Information Engineering, Wuhan University, China - li rs@163.com, 
zqguan@whu.edu.cn 
b School of Government, Peking University, China - tyshen@pku.edu.cn (corresponding author) 
Commission III, WG III/4 
KEYWORDS: Remote Sensing, Urban, Extraction, Texture, DEM, Land use 
ABSTRACT: 
In Beijing, some crop field is similar to urbanized area in spectral space of ETM+ image, and this is an obstacle to extract urbanized 
area of Beijing from ETM+ image. Furthermore, classical texture such as variance can not improve the seperability of such two 
landcovers. This article proposed a skewness based framework to extract the profile of urbanized area, while skewness was seldom 
applied in optical images. Firstly, skewness image was generated from the panchromatic image of ETM+, and it was smoothened 
using low-pass filter. Secondly, skewness and spectral information, from multi-spectral bands, were combined to fully utilized both 
texture and spectral information. Finally, morphological operation and DEM data were employed to perfect the classification result. 
Through visual interpretation, the extracted urbanized area is accurate in large scale, so the “profile” of urban was obtained. At last, 
accuracy assessment showed that accuracy of the skewness based classification was 10% higher than traditional approaches. 
1. INTRODUCTION 
1.1 Application of ETM+ Image in Urbanization Research 
China has experienced a fast urbanization period since the 
opening and reform strategy was implemented. By Using 
remote sensing technique to extract the urbanized area, current 
situation of urbanization can be monitored timely and precisely. 
ETM+ images were obtained by Landsat 7, and NASA provides 
this kind of images from April 15th, 1999 to March 31st, 2004. 
Compared to the TM images obtained by Landsat 4,5, ETM+ 
images has a panchromatic band of 15m in spatial resolution. 
ETM+ image has obvious advantages as follow:(l) The 
panchromatic band has provided abundant texture information 
of landcover. (2) The image can cover an area of 
185KM*170KM, and such large area can include a normal 
metropolis (3) University of Maryland supplies such images 
freely. Therefore, ETM+ images supplied by NASA is an 
effective resource to study the Landcover from 1999 to 2004. 
1.2 Researched Area and its Corresponding Data 
Beijing, motivated by economic growth, transportation 
advancement and 2008 Olympic Games, is experiencing an 
incredible urbanization. This research employed an ETM+ 
image (Figure 1, where the black part represents the area 
outside the image, Path N0:124/033, Date:05/07/2000) and 
DEM (Figure 2) data to study its urbanization. 
Figure 1. True color ETM+ image of Beijing