ANALYSIS AND CORRECTION TECHNIQUE OF 
TOPOGRAPHIC EFFECT IN DIGITAL REMOTE SENSING IMAGE 
Liangeai Chu Yingcheng Li 
Research Institute of Surveying and Mapping, Beijing 100039, China 
ABSTRACT 
Topographic effect on remote sensed data in hilly and mountainous areas prevents from | 
quantitative analysis, automated classification, scene segmentation and feature extraction of | 
satellite images. The feature and rules of topographic effect on digital remote sensing image 
are analysed, and the models for topographic effect correction are described in this paper. | 
Mainly the existing models for topographic effect correction are improved and a set of | 
software for topographic effect correction on microcomputer is developed, The satisfactory | 
experiment results of topographic effect correction of TM images are obtained, | 
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Keywords: topographic effect topographic effect correction 
digital remote sensing image digital elevation model (DEM) 
radiative trsanfer theory 
The analysis and application of remote sensed À digital remote sensing image is radiance of a 
imagery, especially, accurate quantitative terrain element, detected and recorded by sensor, 
analysis and application, are mainly based on and is expressed by formula (1). 
the spectral signature of objects. However, 
spectral information of objects in image is La = p' (à) + En + À e (à) (1) | 
subject to disturbance of many factors, e. g. | 
topographic effect, atmospheric influence and Essentially, the topographic effect in remote | are 
ete. The topographic effect is more evident in sensed imagery is a change of emitted | 5 
the hilly and mountainous area, Due to the electromagnetic energy caused by topography | e, | 
topographic effect, the terrain elements of during transmission, There are two parts | | 
same coverage have different irradiance, included mainly in the formula (1): | 
which reflected in different grey values in | 
image. It seriously affects the image spectral (i). p'(X)—bidirectional reflection factor 
contents, reduces the accuracy of information of terrain element. It expresses the | Thus, 
extraction, leads to misclassification even spectral reflection characteristic of | ge om! 
unclassification, and becames a main obstacle terrain features, and deponds on the | tota 
of quantitative remote sensing application. characteristics of the features. p°’ (2) Ther 
is subject to the topographic influence | flat 
Investigation of topographic effect in remote to some extend, which shall be discussed | expri 
sensed images is aimed at reduction of such in the next paragraph. | terri 
effect and enhancing the image spectral | 
information, This investigation constitutes an (ii), Ea — total irradiance of a terrain | 1-3. 
important fundamental topic of quantitative element. It is a sum of possible 
remote sensing application. irradiances received by the element, and | In hi 
is the main part affected by topography. rece! 
1. TOPOGRAPHIC EFFECT ANALYSIS Topographic effect of En is related to into 
the terrain topography ( orientation and 
The topographic effect in digital remote environment of terrain element) and | a. ! 
sensing imagery is defined as: a sensor characteristics of radiation source, | b. ! 
response change of total irradiance of Analysis of topographic effect of En is | e? 
inclined terrain element with respect to the main concern of the paragraph. | 6 
horizontal one, and it is a function of | 
orientation between the iclined terrain element 1-1. Flat area | In th 
, light source and sensor position (Holben and | diffe 
Justice, 1981). The degree of topographic In flat area the total irradiance received by | irran 
effect is determined by  comparision of a terrain element ( Ex ) can be divided into | is a 
irradiance or grey value of the inclined and (Fig. 1-a) : hilly 
horizontal terrain elements of the same | 
coverage. | 
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