TRIPLET-MATCHING FOR DEM GENERATION WITH PRISM, ALOS 
---- À Case Study using Air-Borne Three Line Scanner Data 
Tianen CHEN ', Ryosuke SHIBASAKI *, Koichi TSUNO”*, and Kazuya MORITA 
* Shibasaki Lab, Institute of Industrial Science, University of Tokyo 
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, JAPAN 
shiba@skl.iis.u-tokyo.ac.jp 
" STARLABO Corporation 
1-20-1, Sanshin BLDG, Shibuya, Shibuya-ku, Tokyo 150-0002, JAPAN 
chentian@iis.u-tokyo.ac.jp 
Commission ITI, WG I11/2 
KEY WORDS: PRISM/ALOS, Three-Line Scanner, Pyramid Image, Triplet Image Matching, DEM Generation 
ABSTRACT: 
For natural landscape, area-based matching can be successfully applied because the elevation is undulating rather gently. On the 
other hands, urban areas with the mixture of artificial structures such as buildings and natural landscape, where the elevation tends to 
have steeper changes, conventional area-based matching may not be successful. Many computer vision papers demonstrated 
matching methods based on features such as edge and regions extracted from images have much better performance for artificial 
structures. 2.5 m ground resolution of PRISM, however, may not be enough to extract detailed features enough to represent artificial 
structures. This may suggest the combination of area-based and feature-based matching approach can be more appropriate for ALOS 
PRISM data. This paper presents the results of experiments on the combination of the two approaches using simulated PRISM image 
generated from air-borne image sensor, TLS (Three Line Scanner). 
1. INTRODUCTION 
A number of space-borne scanner systems using solid-state 
linear array of detectors have been successfully in operation for 
stereoscopic mapping since SPOT-1 was launched in 1986. 
Different from SPOT-1 and SPOT-2 launched in 1990, which 
are collecting stereo images by side-looking push-broom mode 
and have certain disadvantages, for example different 
atmospheric conditions can prevail on different passes, thus 
degrading the stereo images, MOMS (Modular Optoelectronic 
Multispectral Stereo Scanner)-02/D2, MEOSS (Monocular 
Electro-Optical Stereo Scanner), HRSC (High Resolution 
Stereo Cameras) and IKONOS-1 of Spacelmaging collect 
digital along-track stereoscopic imagery using a three-line 
camera (Ebner ef al., 1991 and 1992; Fraser and Shao, 1996; 
Frisch et al., 1998; Ebner et al., 1999; Kornus ef al., 2000). 
PRISM (Figure 1) of ALOS to be launched in 2004 has three 
radiometers for Forward, Nadir and Backward viewing to 
collect along-track stereoscopic imagery at 2.5m ground 
resolution on 691.65km orbit altitude above equator for 
1:25,000 mapping. Each radiometer has field of view with over 
70km. Observation width is switched to 70km and 35km 
respectively in the Nadir viewing radiometer, and in the 
Forward and Backward viewing radiometer, it is 35km. When 
70km observation mode of the Nadir is selected, only the 
observation data of the Backward radiometer can be acquired 
simultaneously. To correct distortion of observation views due 
to the Earth’s rotation, even if satellite dose not carry out the 
yaw steering to correct it PRISM has an Earth rotation 
correction function and obtains images by selecting 
automatically the best image extraction position according to 
the satellite position information provided from the satellite 
system. Table 1 lists its main characters. 
  
   
    
Forward 
Backward 
Figure 1. Illustration of the PRISM 
  
  
  
This article deals with the extraction of height information from 
PRISM simulated imagery generated from SI-100 which is an 
airborne  three-line-scanner developed by | STARLABO 
Corporation jointly with University of Tokyo in 2000 (Chen ef 
al., 2003). Table 2 lists the main characters of SI-100. 
   
  
   
   
  
  
    
    
   
   
  
  
  
  
   
   
  
   
   
  
   
  
  
  
  
  
  
   
   
  
   
  
  
  
   
  
  
  
  
  
   
  
   
   
  
   
  
   
   
    
    
   
   
  
    
   
   
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