3.1. Reflectance data and MNF transformed data
MNF transformation condensed spectral variation into smaller
set of bands (Fig. 2). The classification tests with 8–14 MNF bands
yielded the highest pixel-wise OA (90.8%) with the first 12 MNF
bands (Table 2). As a comparison, the pixel-wise OA achieved with
all 64 spectral bands was 71.1%. The first 12 MNF bands were thus
used in the later classifications.
3.2. Effect of probability threshold
The pixel-wise OA remained constant (90.8%) for up to PT
0.3 while all pixels were classified (Fig. 3a). As PT was further
increased, OA started to increase while the percentage of unclassified
vegetation pixels in image increased, respectively. By visual
interpretation, it was noted that the validation pixels that were first
left unclassified were on the edges of tree crowns and in other areas
where it was hard to find pure pixels, i.e., pixels which represent
only one species without shadowing or major soil effects. Polygonwise
OA increased slightly slower than the pixel-wise OA as the
PT was increased. The percentage of unclassified pixels increased
faster within non-target polygons than within target polygons as
PT was increased (Fig. 3b). Similarly, the percentage of unclassified
non-target polygons increased faster than the percentage of
unclassified target polygons (Fig. 3b).
3.3. Classification maps of the study area