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Title
Proceedings of the Symposium on Global and Environmental Monitoring

grown-up coniferous forest and water, but not
agricultural land and young forest. Areas covered
by clouds, cloud shadows or technical errors in
any of the 36 channels used were excluded from the
mask. Under the mask median values were extracted
from all the 36 channels in 1730 systematically
located windows of 2 by 2 pixels. All the field
surveyed thinnings, except the two stands with
more than 50 % deciduous forest and the seed tree
stands after cutting, were covered by the mask.
The calibration functions, and with them the
measured DN changes, will thus be less
representative for deciduous forest and seed tree
stands.
For each channel at the Landsat acquisitions 1985-
1989, the same channel the previous year were used
as regressor in a linear regression. The
calibration functions where thus of the type:
X(t2,ch i ) = a + b * X(tl,ch i ) (1)
Where:
X = a DN value 0..255
t2 = an aquisition year 1985-1989
tl = t2-l
ch^ = one of the used TM channels
The influence of different definitions of forest
masks and calibration algorithms was tested on
the field surveyed stands before thinning. The
functions finally used were estimated with robust
regression, procedure RREG;NORMAL in Minitab
version 7.2. This procedure is less sensible for
outliers than least squares regression.
2.5 Calculation of standwise spectral changes
The analysis of change in DN values was in this
first version only made when a field surveyed
stand had a valid acquisition both the first
summer before (tl) and the first summer after (t2)
the reported month of cutting. By use of the
calibration fuctions (1), was a mean value at (t2)
predicted from the stand mean value at (tl), for
each stand and channel. This was done for all
valid pairs of aquisitions. The number of
cuttings observed was 41. The number of valid
change measures on the field surveyd stands before
cutting was 105.
The changes in DN is the difference between the
actually measured mean values at (t2) and the
predicted values. Since the stands were cut in
different years, the change values obtained are
mean values for the 5 pairs of summer acquisitions
used.
3. RESULTS
3.1 DN change as a function of thinning grade
Table 3 shows a summary of the field inventory and
the changes in DN. The table is grouped by degree
of thinning. The differences in DN mean values
between the three groups of thinning is small. The
standard deviations fore the thinnings are of the
same order as standard deviations before cut. The
measured DN changes as a function of thinning
grade is illustrated in figure 1.
Table 3. Summary of field inventory and DN changes, grouped by thinning
grade. The measured DN differences for all stands before the year of thinning
are shown in the left column.
All stands
unthinned
Thinnings, grade
19.0 - 30.0 -
29.9 % 39.9 %
40.0 -
51.2 %
Seed tree
stands
74.1-90.4%
Number
of observations:
121
15
14
7
5
Before cutting:
Basal
area (m /ha)
24.0
22.1
26.3
26.5
18.3
Spec.
dist. pine
63 %
68 %
56 %
47 %
76 %
spruce
25 %
23 %
30 %
25 %
20 %
deciduous
12 %
9 %
14 %
28 %
4 %
After cutting*
Basal
area (m /ha)
-
16.7
17.0
14.4
3.3
Spec.
dist. pine
-
72 %
64 %
59 %
100 %
spruce
-
23 %
28 %
26 %
0 %
deciduous
-
5 %
8 %
15 %
0 %
Mean height (m)
-
14.9
15.6
15.4
16.1
Measured-Predicted DN:
TM 1
mean
-0.08
0.43
0.50
0.58
7.84
std
1.30
0.80
1.14
0.98
3.66
TM 2
mean
0.25
0.51
0.35
0.49
4.37
std
0.82
0.63
0.59
0.60
1.12
TM 3
mean
-0.03
1.57
1.12
1.45
14.48
std
0.73
1.26
0.72
1.39
8.86
TM 4
mean
0.46
-0.92
-3.09
-1.81
5.53
std
2.64
2.38
3.74
2.88
2.28
TM 5
mean
0.34
4.82
3.55
4.38
29.80
std
1.36
2.45
2.20
3.41
8.18
TM 7
mean
0.01
2.15
2.00
2.55
13.79
std
0.60
1.17
2.70
1.80
3.72
852