Correction for Off-Nadir Viewing and Topographic Effects 
Sun j i Mural, Toshiaki Hashimoto 
Institute of Industrial Science, University of Tokyo 
7-22 Roppongi, Minatoku, Tokyo 
Japan 
Abstract 
Off-nadir viewing causes some geometric distortions in imagery 
like a tangential distortion, etc. Furthermore, foreshortening or 
layover may happen in case of the off-nadir viewing of an imaging 
radar. 
This paper describes the correction for such kinds of distor 
tions owing to off-nadir viewing and topogragraphic effects. And 
is also introduced the generation of DTM from SPOT stereo pairs. 
1. Introduction 
Here are summarized some kinds of results of studies made by 
the authors. 
The algorithm of geometric correction based on the photogram 
me trie principles has been developed. This can be adopted to both 
high resolution imagery like LANUSAT MSS |1I and low one like MOS-1 
VTIR l2 J . 
SAR imagery is distorted in mountainous areas because of fore 
shortening or layover. The distortions can be eliminated with DTMs 
13 J . 
Since the launch of SPOT, the interest of three dimensional 
measurement; from space has been increasing. The algorithm developed 
by the authors for DTM generation from SPOT stereo pairs is also 
introduced [4] [5]. 
2. Geometric Correction of LANDSAT MSS Imagery 
The methodologies of geometric correction of satellite imagery 
are classified into three; 1) system correction with satellite data 
only, 2) black box correction with GCPs ( ground control points ) 
only and 3) combined method of system correction and black box one. 
It: has been pointed out that the third method is the best in 
accuracy and computing time. However, this method is a little bit 
complicated since it is composed of two steps process. The simul 
taneous process has been developed by treating the position and 
attitude of sensor as the unknown variables, which are determined 
from colinearity equations in photogramme t; ry. 
The position and attitude of sensor can be regarded as exteri 
or orientation parameters in photogramme try. These parameters are a 
function of time or line number since the scanning is performed 
every short time. Although the scanning geometry of MSS is not a 
central projection, it can be treated like central projection when 
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