403 
coniferous forest. Thus, older spruce 
stands from different growth districts 
showed spectral signatures, which 
increased from the Northeast to the 
Southwest of the Regensburg map sheet 
(Fig. 5). Regional changes could also be 
noticed by comparing the signatures of 
three growth districts in the Northeast 
and Southwest of the Nuremberg map 
sheet, and the center of the Augsburg 
map sheet. 
In the visible bands, in reduced form 
also in the near infrared, changes in 
the signatures can well be attributed to 
changes in atmospheric conditions 
(Sagischewski, 1989). The signature 
variances in the short wave infrared 
(bands TM5 and TM7) seem to be mainly 
due to different geological site 
conditions which are partly considered 
in the growth districts (Keil et al., 
1989). 
3.4 Classification and Verification 
For classification purposes, the 
supervised maximum likelihood method was 
applied using bands TM2, TM3, TM4, and 
TM5 of the summer data set. In the map 
sheets of Nuremberg and Augsburg, the TM 
scenes of different pathes (193 and 194) 
were classified separately. The 
classification result could considerably 
be improved by a separate optimization 
in different subregions. These 
subregions, which had to be derived due 
to the regional changes in reflection, 
were based on the digitized map of the 
growth zones/growth districts. Finally 
the results of the subregions and the 
different paths were put together to 
complete maps and superimposed on the 
information from the topographical map 
1:200 000. 
The accuracy of the classification was 
determined in a verification for which 
additional control areas were evaluated, 
partly along with the training areas. By 
using aerial photos which were available 
in parts of the map sheets and control 
areas recorded on the ground, a coverage 
of verification areas, at least in the 
important growth districts, should be 
reached. 
In some growth districts, a major part 
of the reference data had to be used for 
classification, especially for catching 
the various mixture distributions of 
spruce and pine. Therefore the combined 
training areas and control areas 
provided a better coverage of the exten 
ded sites for verification. For this 
SPRUCE STANDS OF DIFFERENT GROWTH DISTRICTS 
JULY 
HISTOGRAn BAND: 1 HISTOGRAM BAND: 2 
HISTOGRAM 
BAND: 3 
HISTOGRAM 
BAND: 
Fig. 5: Regional changes of grey value 
histograms, demonstrated 
for old spruce stands of 
different growth districts.