amount of yellow substance and phytoplankton pigment within the water column
(Babichenko and Poryvkina 1992; Kopilevich et al. 2005; Tuell et al. 2005).
5.2.3 Cost and Application
Coupling a high pulse-rate with low aircraft speed and altitude, allows LiDAR to
cover the ground or seabed with a high density of sample points. This density is
critical in coral reef environments where the terrain is highly variable. The cost of
conducting laser profiling surveys varies greatly with the mapping density desired.
Rohman and Monaco (2005) quoted costs ranging from approximately $375 USD
per sq. km at 5 9 5 m resolution, to $2,000 USD per sq. km at 2 9 2 m resolution; however, since the quotes are now outdated, rather than take these prices as
absolute, it is best to just consider the relevant difference for the two spatial
resolutions. To deliver data that can be used for marine charting, 200 % coverage
of the seabed is demanded to ensure that all obstacles to marine navigation have
been captured and to eliminate artefacts such as fish and flotsam, which will not be
present in both acquisitions. The necessity for double coverage understandably
elevates the cost of a LiDAR survey. For purposes of mapping seabed geomorphology, only a single overpass may be necessary to achieve the desired sounding
spatial density, but typically swath overlap of up to 30 % is used to determine
flightline-to-flightline bias for purposes of quality control and to eliminate data
gaps arising from excessive aircraft roll, yaw, etc.
For surveys\100 sq. km with water depths \50 m, airborne LiDAR is deemed
to be more cost effective than multi-beam acoustic surveys, and faster to acquire
(Rohman and Monaco 2005). As highlighted by Costa et al. (2009), these higher
efficiencies for LiDAR are due to the system’s distinct acquisition geometry, wider
swath-widths, and faster survey speeds. In particular, the average acquisition speed
is much faster for LiDAR, approximately 140 knots, while the average speed of a
survey ship is only 8 knots. Swath-width varies as a function of scan angle and
aircraft altitude, but is nearly independent of water depth (Stephenson and Sinclair
2006). Conversely, the relationship between swath-width and water depth is proportional for multi-beam systems (i.e., the shallower the water, the narrower the
swath and the less area mapped on a single survey line), an undesirable trait when
working in shallow water and/or areas of high bathymetric relief. The fact that
LiDAR is an airborne technology also means that remote areas can be accessed
more rapidly than could be achieved by vessel. However, depending on the range
of the aircraft in relation to the study site and appropriate airfields, LiDAR surveys
over very remote oceanic reef provinces are problematic. It should also be born in
mind, though, that boats may also be excluded from sensitive coral reef areas.
Due to the inherent fine resolution and high density of postings, even a moderately sized LiDAR survey generates vast quantities of data (Table 5.2). This
necessitates both reliable electronic storage and advanced software for processing
and manipulation. These programs and the computers needed to run them are more
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S. J. Purkis and J. C. Brock
(Babichenko and Poryvkina 1992; Kopilevich et al. 2005; Tuell et al. 2005).
5.2.3 Cost and Application
Coupling a high pulse-rate with low aircraft speed and altitude, allows LiDAR to
cover the ground or seabed with a high density of sample points. This density is
critical in coral reef environments where the terrain is highly variable. The cost of
conducting laser profiling surveys varies greatly with the mapping density desired.
Rohman and Monaco (2005) quoted costs ranging from approximately $375 USD
per sq. km at 5 9 5 m resolution, to $2,000 USD per sq. km at 2 9 2 m resolution; however, since the quotes are now outdated, rather than take these prices as
absolute, it is best to just consider the relevant difference for the two spatial
resolutions. To deliver data that can be used for marine charting, 200 % coverage
of the seabed is demanded to ensure that all obstacles to marine navigation have
been captured and to eliminate artefacts such as fish and flotsam, which will not be
present in both acquisitions. The necessity for double coverage understandably
elevates the cost of a LiDAR survey. For purposes of mapping seabed geomorphology, only a single overpass may be necessary to achieve the desired sounding
spatial density, but typically swath overlap of up to 30 % is used to determine
flightline-to-flightline bias for purposes of quality control and to eliminate data
gaps arising from excessive aircraft roll, yaw, etc.
For surveys\100 sq. km with water depths \50 m, airborne LiDAR is deemed
to be more cost effective than multi-beam acoustic surveys, and faster to acquire
(Rohman and Monaco 2005). As highlighted by Costa et al. (2009), these higher
efficiencies for LiDAR are due to the system’s distinct acquisition geometry, wider
swath-widths, and faster survey speeds. In particular, the average acquisition speed
is much faster for LiDAR, approximately 140 knots, while the average speed of a
survey ship is only 8 knots. Swath-width varies as a function of scan angle and
aircraft altitude, but is nearly independent of water depth (Stephenson and Sinclair
2006). Conversely, the relationship between swath-width and water depth is proportional for multi-beam systems (i.e., the shallower the water, the narrower the
swath and the less area mapped on a single survey line), an undesirable trait when
working in shallow water and/or areas of high bathymetric relief. The fact that
LiDAR is an airborne technology also means that remote areas can be accessed
more rapidly than could be achieved by vessel. However, depending on the range
of the aircraft in relation to the study site and appropriate airfields, LiDAR surveys
over very remote oceanic reef provinces are problematic. It should also be born in
mind, though, that boats may also be excluded from sensitive coral reef areas.
Due to the inherent fine resolution and high density of postings, even a moderately sized LiDAR survey generates vast quantities of data (Table 5.2). This
necessitates both reliable electronic storage and advanced software for processing
and manipulation. These programs and the computers needed to run them are more
126
S. J. Purkis and J. C. Brock