54
Reflectance
Figure 5
Reflectance of beech branches of
different damage classes, 5 branches
piled up from trees of 1 = damage
class 0/1; 2,3 = damage class 2/3,
4 = damage class 3
Reflectance of five piled up beech
branches in the visible, description
see figure 5.
which will be superimposed by
secondary effects. The order of
magnitude may vary with the
situation in nature. Branches of the
same damage class showed yellowing of
different degrees, which explains the
spectral variation. The higher spec
tral values for damage class 3 are
the consequence of intensive
yellowing.
In its principle course reflectance
of spruce branches, as displayed in
figure 7, fits with the spectral
reflectance curve of a damaged pine
stand under water stress in the
Stadtwald Frankfurt, see publications
mentioned before. In the visible, as
shown in figure 8, reflectance
increases with increasing damage
class as a consequence of
discolouration (yellowing mainly) of
needles. This tendency was also found
in studies of Hoque et al., 1989, as
part of the multilevel experiment
DLR/GSF. The beginning of the slope
to the NIR plateau shifts towards the
blue and the gradient of the slope
and the height of the NIR plateau, as
well as the water absorption at NIR,
decrease with increasing damage
Reflectance of spruce branches of
different damage classes, five
branches piles up from trees of
1 = damage class 0/1, 2 = damage
Reflectance of five piled up spruce
branches in the visible, description
see figure 7.
level. In the 1,4pm range curves are
crossing. Then the reflectance raises
with increasing damage level.
5. Conclusion
The measurements presented in figure
1-8 show the spectral behaviour of
tree components as a function of
biomass or number of branches piled
up of the same species, the influence
of species and yellowing for healthy
and damaged trees in the spectral
region 0.49-2.50pm. Data from this
spectral region is normally used for
multispectral classification of vege
tation. Further studies of Reinartz,
1989, Kritikos et al., 1988, Kirchhof
et al., 1986, on the separability of
forest and forest damage classes
confirm the result of our spectral
measurements: Good sepration of tree
species and yellowing could be ob
tained by the use of spectral bands
TM2 or TM3, TM4, TM5 and TM7 of the
Thematic Mapper or the corresponding
bands 3 or 5, 7, 9 and 10 of the
Daedalus ATM scanner. For damage
separation of the same species, the
best results were reached with the
ratios TM2/TM4 or TM3/TM4.