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APPLICATION OF FACTOR ANALYSIS 
FOR THE DETERMINATION OF PHYSICAL 
EFFECTS FROM CAUSAL INTERRELATIONS 
OF MULTISPECTRAL BAND SIGNALS 
Rudolf H. Dittel 
Institut fiir Nachrichtentechnik 
DFVLR 
8031 Oberpfaffenhofen 
1. Introduction 
For the purpose of classification the spectral characteristics of different 
surfaces are described by the mean value of the spectral intensities and the 
covariance matrix of all spectral channels selected. Experience shows, that 
increasing the number of spectral channels does not necessarily increase the 
quality of the classification result. For the "visible part" of the electro- 
magnetic spectrum and its vicinity into the UV and near IR region an optimum 
number of four to five spectral channels assuming a bandwidth of 0.5 - 1.0 um, 
has been obtained. The decrease of the classification quality by using an 
extended number of spectral channels results from the partly high linear de- 
pendence of the signals for a scene, combined with statistically occuring 
systematic errors in the signal of either one of the highly correlated channels. 
The statement should not be confused to the conditions of a case, where the 
spectral intensities of only a certain number of different surfaces are highly 
correlated. In these cases the high correlation coefficients do not have any 
influence to the decrease of the classification quality because the different 
surfaces can easily be discriminated by their average spectral radiation inten- 
sities. 
For those cases where the spectral intensities are highly correlated for a 
certain surface either one of these channels does not contribute new informa- 
tion for the explanation of physical and chemical effects that take place. 
Statistically occuring systematic errors are then considered as significant 
information. This is particularly evident if a linear transformation is main- 
tained for the purpose of data reduction and data compression [1]. Thus the