g stages
Roeland de Kok
Classification
The actual change detection is a quite straightforward process. A project with four layers, one being the aerial
photos and the other three the satellite image channels is created and a first segmentation, which considers only
the photo channel, is made. The parameters were a scale parameter of 70 and color and compactness parameter
of 0.3. By using the nearest neighbor classifier containing spectral as well as texture and brightness features, the
image objects were classified to forest and non-forest. The availability of the object variability makes this
extraction of a forest mask much different from density slicing in a normal panchromatic imagery. The statistical
parameters of the forest area encapsulate the textural information of the forest. This principle difference cannot
be overstressed.
A second segmentation that uses the three SPOT channels provides the second level. The scale parameter was set
to 15 and the Color and compactness parameters were set to 0.3 each. In this level all objects with super objects -
of forest and the spectral information of non-forest in the SPOT channels are classified as deforest classes and
subsequently merged.
In the resulting level, a final classification was done, separating forest, non-forest and deforested areas. This time
an additional size criterion was included in the classification, eliminating all deforest objects smaller than 800
pixels. So, the focus could be set to the objects of interest, the substantial changes in the forest vegetation.
The result is a map, which shows all major forest losses over the past sixty years. By varying the size parameter
in the last classification, the scale of deforested areas that are of interest can be varied.
Forest Non-forest
Deforested Areas
1960 1960 1960 |+| 1996
Four layer image Separation of forest and Classification of
comprised of the three
SPOT channels and one
aerial photo.
non-forest by means of
classification of objects
derived from the aerial
photo.
deforested areas by the
use of objects derived
from the SPOT channels
in combination with the
preceding classification
Figure 6: Aerial photo classification stages
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.
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