be spectrally confused with seagrass and some algal
habitats, coral reefs may be spatially distinguished. This
is because their location (context) within the reef land-
scape is usually con®ned to the seaward margin of the
coastal zone (i.e. fringing reef), where wave exposure is
moderate to high. In this study, contextual discrimina-
tion of algal and seagrass habitats was dicult because
gradients of exposure were generally less obvious and it
was not easy to predict the location of habitats.
Although Landsat TM and SPOT sensors provided
similar accuracies to aerial photography for reef habitat-
mapping with moderate detail, there are other reasons
for choosing satellite imagery in preference to photog-
raphy. First, the generation of a geo-coded map is sim-
pler when based on a single satellite image than when
faced with mosaicing and geo-coding, for example, ®fty
aerial photographs. Second, the time required to visually
interpret and digitise aerial photography is likely to be 1
to 2 orders of magnitude greater than that required for
processing digital satellite imagery. Third, existing aerial
photographs for a particular study site may be quite old
(especially if they were collected for the purposes of
cartographic mapping), and satellite imagery will gen-
erally provide a more recent data source. This does,
however, open up the wider issue of cost-eectiveness.
If new imagery is required for a site, the most cost-
eective solution depends on the mapping objectives,
required accuracy, the size of the area, climate of the
area (e.g. persistence of cloud cover), the volume of data
required, and the availability of technical expertise and
equipment. An analysis of these issues is beyond the
scope of this paper and will be reported at a later date.
However, a few simple rules emerge (Table 4).
Fine habitat-discrimination
The results presented in this study suggest that satellite
imagery is not well suited to detailed mapping of benthic
habitats; aerial photography provided consistently
greater accuracies. This conclusion is in agreement with
Bainbridge and Reichelt (1989), who concluded that
be spectrally confused with seagrass and some algal
habitats, coral reefs may be spatially distinguished. This
is because their location (context) within the reef land-
scape is usually con®ned to the seaward margin of the
coastal zone (i.e. fringing reef), where wave exposure is
moderate to high. In this study, contextual discrimina-
tion of algal and seagrass habitats was dicult because
gradients of exposure were generally less obvious and it
was not easy to predict the location of habitats.
Although Landsat TM and SPOT sensors provided
similar accuracies to aerial photography for reef habitat-
mapping with moderate detail, there are other reasons
for choosing satellite imagery in preference to photog-
raphy. First, the generation of a geo-coded map is sim-
pler when based on a single satellite image than when
faced with mosaicing and geo-coding, for example, ®fty
aerial photographs. Second, the time required to visually
interpret and digitise aerial photography is likely to be 1
to 2 orders of magnitude greater than that required for
processing digital satellite imagery. Third, existing aerial
photographs for a particular study site may be quite old
(especially if they were collected for the purposes of
cartographic mapping), and satellite imagery will gen-
erally provide a more recent data source. This does,
however, open up the wider issue of cost-eectiveness.
If new imagery is required for a site, the most cost-
eective solution depends on the mapping objectives,
required accuracy, the size of the area, climate of the
area (e.g. persistence of cloud cover), the volume of data
required, and the availability of technical expertise and
equipment. An analysis of these issues is beyond the
scope of this paper and will be reported at a later date.
However, a few simple rules emerge (Table 4).
Fine habitat-discrimination
The results presented in this study suggest that satellite
imagery is not well suited to detailed mapping of benthic
habitats; aerial photography provided consistently
greater accuracies. This conclusion is in agreement with
Bainbridge and Reichelt (1989), who concluded that
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