characteristics visible instereoscopic view 
refer to the three dimensional appearence 
of a crown in aerial photographs. No matter 
what type of film or emulsion is being used, 
the shape of the crown is always visible. 
The characteristic shape types can easily be 
assessed. 
- The description of the shape includes (a) 
the form of crowns, (b) their coarse struc 
ture and (c) their fine structure. 
- The parameter "colour” is generally ana 
lysed according (a) colour distribution, (b.) 
saturation and brightness, (c) colour tone, 
the only factor still to be adepted to the 
conditions of the flight. 
- Discolouration symptoms (chlorosis) are de 
termined seperatly in four steps (Table 2). 
The combination of both kinds of symptoms 
results in the final classification of the 
crown condition, analogous to the system 
being used for terrestrial inventories (see 
section 1.1). 
- The description of the symptoms is supple 
mented by a photographic documentation of 
representative trees compiled both in 
field-work and aerial photography, as well 
as by a. graphic appendix. 
3 CONCLUSION 
After three years of intensiv work the team 
Arbeitsgruppe Forstlicher Luftbildinterpreten 
has now interpretation keys to classify fo 
rest decline for four main tree species in 
Central Europe: spruce, beech, oak and pine 
/1/. A manual in five languages based on the 
se keys is now being developt with the spon 
sorship of the European Community - a fact 
underlining the high standard and progress of 
the work of the group. 
The application of this new type of interpre 
tation keys improves the standardization of 
evaluation methods and provides the basis for 
comparison between different inventories. 
To improve the quality of furture interpre 
tation results ist is recommended to stan 
dardize the quality of all aerial imagery 
surveys, to harmonise the applied interpreta 
tion keys and, most of all, to attune the in 
terpreters to the same criteria and to con 
trol their interpretation results /6/. 
Table 2. 
Interpretation Key for "Clorosis" as a supplementary characteristic for the classification of 
Norway Spruce 
Chlorosis 
Level 
%-Proportion 
of Canopy 
with Chlorosis 
Colour Characteristic in 
CIR-Aerial Photographs 
Change of 
(without 
Initial Level 
Chlorosis) 
general 
specific 
0 
1 
2 
3 
0 
< 10 
no change of the colour characteris 
tics specific for damage levels 
0 
1 
2 
3 
1 
11 to 25 
small areas 
of red-white or 
pink marblings 
0 
1 
2 
3 
2 
26 to 60 
compact, large 
areas of pink or 
white 
1 
2 
3 
3 
3 
> 60 
most of the crown 
or entire crown 
whitish 
2 
2 
3 
3 
756