When complete coverage of the seabed is required, SSS and MBES are the tools of
choice. MBES are the most attractive system for mapping coral reef habitats in
depths 30 m and greater, where the wide swath (3–79 depth) allows for costeffective data acquisition. The dense narrow-beam point bathymetry of a MBES can
be interpolated into high-resolution hill-shaded topographic maps that are visually
intuitive, informative, and GIS-ready. MBES topographic maps can also be complemented by slope analysis and texture, as well as integrated with analyses of
backscatter intensity. Such maps are ideal for expert-driven visual interpretation of
geomorphological features, delineation of MPA boundaries, or identification of
essential fish habitat. In shallow waters, PDBS produces bathymetric and backscatter
intensity information similar to MBES, but at greater swath width (10–129 depth).
SSS is less expensive to own and operate than MBES and can be used from submeter to 100s of meters depth, but the quality of the 2D imagery is generally less
consistent than MBES and lacks the bathymetric component. Also, the signal
amplitude of SSS frequently varies significantly within a survey. The backscatter
intensity of individual swaths must be balanced to achieve a consistent composite
image, which is best achieved if there are distinct seabed features displaying
consistent characteristic backscatter responses to be used as reference standards.
Kenny et al. (2003) discussed SSS versus MBES trade-offs, including coverage,
survey depth, and object detection limits. The imagery produced by SSS and
MBES swath systems can both be used to deduce dynamic processes (e.g., sediment transport deduced from the directionality of seabed forms). Extracting textural properties (i.e., mean, standard deviation, and higher order moments,
amplitude quantiles and histograms, power spectral ratio, grey-level co-occurrence
features, fractal dimension) from SSS and MBES imagery also allows for statistical benthic habitat classification.
ASC systems are relatively inexpensive to purchase, operate, deploy, and process, but their along-track bathymetry does not make them suitable for producing
full coverage maps of spatially complex habitats. For example, at 15 m depth and
50 m line spacing, a narrow (10°) beamwidth transducer would cover only 5 % of
the area between lines. Interpolating such large information gaps results in a low
resolution bathymetric surface and the potential for generating false features,
particularly when surveying along parallel lines. However, the temporally resolved
waveforms and fixed-geometry of single-beam systems allows for direct detection
of benthic habitats and other environmental properties such as vegetative biomass,
epibiotic canopy height, or suspended solids in the water column. In situations with
a relatively homogeneous setting, such as some back reef lagoons, an ASC system
could be used to map the abundance and distribution of seagrass, epibiota, infauna,
or sediment grain size. An ASC system could also be used to complement habitat
maps produced from MBES or LiDAR topography. For example, the ASC system
could be used to map the abundance and distribution of epibiota, adding a biological component to the topographic map. ASC systems are also useful for identifying essential fish habitat, either by bottom classification or from measures
derived from the along-track bathymetry (e.g., rugosity or slope analysis).
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choice. MBES are the most attractive system for mapping coral reef habitats in
depths 30 m and greater, where the wide swath (3–79 depth) allows for costeffective data acquisition. The dense narrow-beam point bathymetry of a MBES can
be interpolated into high-resolution hill-shaded topographic maps that are visually
intuitive, informative, and GIS-ready. MBES topographic maps can also be complemented by slope analysis and texture, as well as integrated with analyses of
backscatter intensity. Such maps are ideal for expert-driven visual interpretation of
geomorphological features, delineation of MPA boundaries, or identification of
essential fish habitat. In shallow waters, PDBS produces bathymetric and backscatter
intensity information similar to MBES, but at greater swath width (10–129 depth).
SSS is less expensive to own and operate than MBES and can be used from submeter to 100s of meters depth, but the quality of the 2D imagery is generally less
consistent than MBES and lacks the bathymetric component. Also, the signal
amplitude of SSS frequently varies significantly within a survey. The backscatter
intensity of individual swaths must be balanced to achieve a consistent composite
image, which is best achieved if there are distinct seabed features displaying
consistent characteristic backscatter responses to be used as reference standards.
Kenny et al. (2003) discussed SSS versus MBES trade-offs, including coverage,
survey depth, and object detection limits. The imagery produced by SSS and
MBES swath systems can both be used to deduce dynamic processes (e.g., sediment transport deduced from the directionality of seabed forms). Extracting textural properties (i.e., mean, standard deviation, and higher order moments,
amplitude quantiles and histograms, power spectral ratio, grey-level co-occurrence
features, fractal dimension) from SSS and MBES imagery also allows for statistical benthic habitat classification.
ASC systems are relatively inexpensive to purchase, operate, deploy, and process, but their along-track bathymetry does not make them suitable for producing
full coverage maps of spatially complex habitats. For example, at 15 m depth and
50 m line spacing, a narrow (10°) beamwidth transducer would cover only 5 % of
the area between lines. Interpolating such large information gaps results in a low
resolution bathymetric surface and the potential for generating false features,
particularly when surveying along parallel lines. However, the temporally resolved
waveforms and fixed-geometry of single-beam systems allows for direct detection
of benthic habitats and other environmental properties such as vegetative biomass,
epibiotic canopy height, or suspended solids in the water column. In situations with
a relatively homogeneous setting, such as some back reef lagoons, an ASC system
could be used to map the abundance and distribution of seagrass, epibiota, infauna,
or sediment grain size. An ASC system could also be used to complement habitat
maps produced from MBES or LiDAR topography. For example, the ASC system
could be used to map the abundance and distribution of epibiota, adding a biological component to the topographic map. ASC systems are also useful for identifying essential fish habitat, either by bottom classification or from measures
derived from the along-track bathymetry (e.g., rugosity or slope analysis).
226
G. Foster et al.