Accuracy requirements
Before speci®c accuracies and the suitability of various
satellite sensors for habitat mapping are discussed, it is
necessary to comment on the importance of accuracy. It
is extremely dicult to suggest a threshold accuracy
which may be considered adequate or acceptable ± even
for the purposes of general guidance. As scientists or
decision-makers, our ®rst instinct might be to think in
terms of statistical error margins where a permissible
Type I error may be <5%. In most situations, however,
it would be unrealistic to expect map accuracies to ex-
ceed 95%. This is because habitat maps impose an or-
dered classi®cation on a benthos which actually exhibits
semi-continuous gradients of structure and composition
(usually with depth or wave exposure). There is, there-
fore, a degree of natural uncertainty in the placement of
most habitat boundaries and this incurs error.
An alternative viewpoint might be to ask whether an
accuracy of (say) 40% is worthwhile when the alterna-
tive is no mapped information at all? This is a dicult
question to answer at present. The solution may become
clearer once research addresses the economic importance
of habitat data in various coastal management contexts.
Similarly, insight might be drawn from the consequences
of taking inappropriate management action on the basis
of inaccurate information. However, to the best of our
knowledge, such data are not available.
Given the arguments above, we have elected to use a
dierent type of accuracy benchmark; that achieved with
aerial photography. This is because aerial photography
has been the conventional mapping medium for many
decades and is widely available.
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