652 - 
DENSITY ANALYSIS OF TERRAIN; AN EXAMPLE 
Quantitative density analysis can be performed in various ways. Point measure 
ment using a simple densitometer is the simplest solution. Line measurement 
by way of a micro-densitometer producing densitometric profiles gives more in 
formation but the most satisfactory approach is in establishing equidensity lines 
or density "slices’' that cover the whole image. The absolute density values thus 
obtained are in many cases rather irrelevant and strongly affected by the photo 
graphic processing of the image. Fortunately, however, the relative density dif 
ferences are more important for purposes of mapping of terrain than the absolute 
values. 
The principles of equidensitometry are given by LAU and KRUG (1968). The 
various methods are based on a re-photographing of the original photo in such a 
way that the picture is divided into a number of density classes, each one of which 
represents a well-defined density range of known absolute values. A completely 
quantitative analysis of the density distribution is thus possible. The oldest, so- 
called Sabattier method, involves the exposure of a photographic emulsion and its 
partial development. The wet emulsion is then exposed to diffuse light for some 
period of time whereafter the development is completed. REINHOLD (1967) used 
this method in his study of some poorly drained areas in the DDR. Another proce 
dure is the positive-negative method in which transparent negative and positive 
photographic images are superposed on each other, either exactly or with a slight 
misfit. 
Both methods are rather lengthy and the results obtained are difficult to repro 
duce. A special equidensitometric film, the AGFA contour professional film, 
came on the market in 1970 which gives more rapid and reproduceable results. 
The original negative of the diapositive is copied on this special film using a 
yellow filter of known characteristics. The exposure time used determines the 
density class recorded and the type of yellow filter affects the density range of 
every class. By repeating the process, equidensities of the 2nd and 3rd order can 
be obtained (RANZ-SCHNEIDER, 1970; WIECZOVEK, 1972). 
A new development is the advent of optical computers such as the Isodensitracer 
(Joyce-Loebl), the Photodata Quantizer (Bausch and Lomb) and the Quantimet 720 
(Imanco Ltd. ). The following example of quantitative density analysis for the 
study of terrain has been carried out using Quantimet 720 equipment. It clearly 
shows the possibilities and limitations of the approach for geomorphological pur 
poses. 
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