structural, chemical and process attributes (Hochberg and Atkinson 2000; Hedley
and Mumby 2002; Hochberg et al. 2003, 2004; Mumby et al. 2004b).
Mapping coral reef features, either by discriminating benthic features or estimating biophysical properties, such as depth and pigment concentration, requires
remotely sensed data with the appropriate spectral and spatial dimensions. Once
these are identified, a suitable image processing algorithm can be selected. For
mapping coral reef features, a significant amount of work has been completed
globally to show that as you increase the number of spectral bands and decrease the
pixel size the greater number of benthic and substrate cover types you will be able to
map (Andréfouët et al. 2003). This corresponds to a progression from mapping reef/
non-reef, to mapping geomorphic zones and reef biotope zones, to mapping benthic
communities. A similar pattern is observed when mapping coral reef biophysical
properties, whether in the water column, benthos or substrate; increasing the
number of spectral bands enables more detailed and precise estimation of biophysical properties. Large numbers of spectral bands with narrow band widths also
permits specific absorption features or inflection points, produced by photosynthetic
or non-photosynthetic pigments, to be resolved (Hochberg and Atkinson 2000,
2008; Hedley and Mumby 2002; Hochberg et al. 2003, 2004; Mumby et al. 2004b;
Hochberg and Atkinson 2008). Research on hydro-optics in water bodies and photosystems in corals has established which wavelength regions are absorbed by specific
chemicals and processes; hence reflectance signatures resolving these features can
be used in algorithms to estimate or map them for each pixel. Figure 1.5 further
illustrates the relative differences in spectral content for multispectral versus
hyperspectral images using example data from Heron Reef, Australia.
1.2.3 Photography (Film and Digital)
Aerial and space photography in its film-based form cannot display a spectralreflectance signature; however their simple format and long term collection
worldwide make them a unique resource for coral reef mapping and monitoring
over time. Film based products are typically transformed to maps of benthic cover
through systematic interpretation keys for specific features based on subjective,
context specific, visual interpretation cues. To accomplish this, photographs, or
negatives, are often scanned into digital format and processed into maps using
image processing or geographic information system (GIS) software. If historic,
thematically simple maps (e.g., geomorphic zones, sand, coral, etc.) are required,
aerial photographs are highly suitable for this application. Any detailed mapping
of coral reef features using photography requires extensive site-specific context
and field knowledge, along with high spatial resolution (\1:5,000 scale) aerial
photographs in either color or black and white formats.
Aside from field survey data, photography is often the only systematically
collected, long term archive of spatial information available for coral reefs in
many areas. It should be noted, however, that standard format photographs contain
1 Visible and Infrared Overview
15
and Mumby 2002; Hochberg et al. 2003, 2004; Mumby et al. 2004b).
Mapping coral reef features, either by discriminating benthic features or estimating biophysical properties, such as depth and pigment concentration, requires
remotely sensed data with the appropriate spectral and spatial dimensions. Once
these are identified, a suitable image processing algorithm can be selected. For
mapping coral reef features, a significant amount of work has been completed
globally to show that as you increase the number of spectral bands and decrease the
pixel size the greater number of benthic and substrate cover types you will be able to
map (Andréfouët et al. 2003). This corresponds to a progression from mapping reef/
non-reef, to mapping geomorphic zones and reef biotope zones, to mapping benthic
communities. A similar pattern is observed when mapping coral reef biophysical
properties, whether in the water column, benthos or substrate; increasing the
number of spectral bands enables more detailed and precise estimation of biophysical properties. Large numbers of spectral bands with narrow band widths also
permits specific absorption features or inflection points, produced by photosynthetic
or non-photosynthetic pigments, to be resolved (Hochberg and Atkinson 2000,
2008; Hedley and Mumby 2002; Hochberg et al. 2003, 2004; Mumby et al. 2004b;
Hochberg and Atkinson 2008). Research on hydro-optics in water bodies and photosystems in corals has established which wavelength regions are absorbed by specific
chemicals and processes; hence reflectance signatures resolving these features can
be used in algorithms to estimate or map them for each pixel. Figure 1.5 further
illustrates the relative differences in spectral content for multispectral versus
hyperspectral images using example data from Heron Reef, Australia.
1.2.3 Photography (Film and Digital)
Aerial and space photography in its film-based form cannot display a spectralreflectance signature; however their simple format and long term collection
worldwide make them a unique resource for coral reef mapping and monitoring
over time. Film based products are typically transformed to maps of benthic cover
through systematic interpretation keys for specific features based on subjective,
context specific, visual interpretation cues. To accomplish this, photographs, or
negatives, are often scanned into digital format and processed into maps using
image processing or geographic information system (GIS) software. If historic,
thematically simple maps (e.g., geomorphic zones, sand, coral, etc.) are required,
aerial photographs are highly suitable for this application. Any detailed mapping
of coral reef features using photography requires extensive site-specific context
and field knowledge, along with high spatial resolution (\1:5,000 scale) aerial
photographs in either color or black and white formats.
Aside from field survey data, photography is often the only systematically
collected, long term archive of spatial information available for coral reefs in
many areas. It should be noted, however, that standard format photographs contain
1 Visible and Infrared Overview
15