Introduction 
Aerial photography is a widely used technique for inventories and 
observations of forests (Hildebrandt, 1977). The aerial photographs 
are usually evaluated and interpreted visually by specially trained, 
experienced photointerpreters. 
Many attempts have been reported to support or even to substitute 
the manual, subjective methods by automatic, computerized, objective 
interpretation techniques (Kalensky and Wightman, 1976). For a 
reliable identification and classification of forest stands, the 
classification process has to be based on both spectral and textural 
parameters. These parameters, besides from being relevant for 
the classification process, should satisfy certain requirements: 
a) The extraction of the parameters from photographs should be 
possible at a reasonable expenditure. b) The parameters should 
show little variation with the angle of view, or they should at least 
be related to the angle of view in a simple manner. 
In this contribution, the use of the image analyzer Quantimet 720 
of IMANCO for the purpose of extracting textural signatures from 
forest aerial photographs is discussed. It is shown that some of the 
textural parameters that can be obtained with the Quantimet satisfy 
the above-mentioned requirements. The usefulness of these para- 
meters for automatic tree species recognition is demonstrated. 
Test data 
The photographs used for this investigation were taken in 1975 in 
an area approximately 60 km south of Vienna. This forest area, 
which is very intensively managed, is characterized by an inhomo- 
geneous distribution of species. It also has rather complex relief 
features with an average gradient of slope of 15° to 20°. It was, 
nevertheless, selected for this study for two reasons: This forest 
area is used by the forestry institutes of the Universität für Boden- 
kultur for instructional purposes. Many ground investigations are 
being performed there continuously, so that, from the point of view 
of available ground data, it is an ideal test site. The second reason 
for choosing this test area was that, in addition to aerial photo- 
graphs, multispectral scanner data had been acquired in this area. 
Comparative studies of the performance of these two remote sensing 
systems can therefore be performed. 
The photographs used for this study were taken on Aerochrome 
Infrared film 2443 with a Wild RC-10 camera equipped with an 
Aviotar f-30 cm lens, from a height of approximately