761 
statistical parameters (= digital). 
Vertical profiles are the most obvious analog representation of the model. 
Fig. 3 shows randomly selected vertical profiles from a very heterogenous 
mixed stand of various species and ages (test area Freiburg i). The figure 
gives the computer output of the profiles. As mentioned before the distances 
between points in x and y have been 0,3 mm in the stereomodel = 1,5 m in 
nature. The test area was 95 m x 63 m in size. Therefore we got a model con 
sisting of 2 646 points (x,y,z) and for the analog characterization of the 
surfaces’s roughness and structure 42 vertical profiles in y- and 63 profiles 
in x-direction. One can imagine that the information about the surface is 
very detailed. 
A good analog model of the entire surface arises from the combination of all 
vertical profiles in x and y (Fig. 4). It allows the approximated calculation 
of the extent of the entire surface. For this purpose it is useful to put 
diagonal lines between the profiles as one can see in Fig. 4c. By relatively 
simple geometric formulas one can calculate the area-extent of the surface. 
Along with these analog descriptions the surface and its roughness can be 
characterized by statistical parameters, so by following datas: 
the relation of z and z - z . 
max mm 
the variance of z. and the variance - coefficient 
l 
the frequency distribution of z^ 
Then particularly by the more useful values of M Az of neighbor-points" , 
especially 
the A z of neighbor-points 
the variance of A z, 
the frequency distribution of Az, (see fig. 5) 
In flat areas all these parameters are useful. In hilly or mountainous regions 
the usefulness of the z. parameters depends on the question which should be 
answered with the investigation. In any case, however, the parameters of Az, 
of neighbor-points are important. They provide the best information, both for 
comparisons between the roughness of different cover- and surface-types and 
for the characterization of the detailed roughness by absolute figures. 
CONCLUSION 
The paper introduced and discussed an approach for a digital surface model. 
It may be necessary to improve and or adapt it to the special research needs 
in the diverse fields of research as well as with regard to regional aspects 
or the special properties of the objects and their surface characteristics. 
In any case the model can be helpful for topoclimatic,biophysical, ecological, 
micromorphological or forestry studies.