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Figure 54: Aerial view of marsh test 3
The values for the red colour band for this smaller section of known marsh were
not consistent with all the other test polygons, with a small rise from shade values
to those expected for marsh. This suggests, to a greater extent than the larger
samples, that it is difficult to automatically classify marsh based on spectral values
alone. The classification of this type of polygon must, as a result, take place
towards the end of the search –so that all known values, including those
automatically registered in the algorithm (such as pasture and bog) are first
removed from the pool of areas being studied. It should be noted that this part of
the study is not intended to be an exhaustive search for a means of automatically
identifying marsh, but to show that it is possible when an aerial image is divided
into discrete small area polygons –other factors, for example the percentage of
rough pasture and water polygons in the same region of the image (taken from the
vector data) could potentially be used increase accuracy in identifying this type of
ground cover.
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