represents the state-of-the-art for reef-scale seafloor topography and offers an
unparalleled means of mathematically quantifying reef geomorphology.
While corals are the architects and builders, coral reefs are not, by any means,
made of corals alone. In fact, many other calcareous organisms, both animal and
plant, may contribute more to the volume of a reef than do the corals (Blanchon
et al. 1997; Wood 1999; Braithwaite et al. 2000; Perry et al. 2009). In near-shore
systems, there may also be considerable quantities of siliciclastic sediments within
the reef environment. Such settings are commonly termed ‘mixed’ carbonate
systems. As depicted in Fig. 5.7, the bedforms that these sediments create can be
appraised via bathymetric LiDAR. In the figure, reef features are easily discerned
in the IKONOS satellite imagery because they are spectrally different from the
surrounding substrate, as well as by LiDAR because they have considerable
topographic relief. By contrast, sedimentary bedforms are not spectrally distinct
and are unresolved by the satellite imagery, but visible by virtue of the differences
in relief observed in the LiDAR. This same figure demonstrates a further advantage of LiDAR over satellite imagery for reef mapping; in the southern portion of
the two images is an expansive reef complex, which due to depth cannot be seen
via IKONOS, but is intricately resolved in the LiDAR survey.
Naturally occurring bedforms include sediment waves, submerged aquatic
vegetation root masses, and obstruction scour and deposits. The structure of these
features can be related to factors such as sediment supply and grain size, as well as
serving as a useful proxy for wave, current, and tidal characteristics in the coastal
zone (the region depicted in Fig. 5.7 is clearly subjected to very rigorous tidal
currents). Furthermore, repeat coverage with time-separated LiDAR surveys
allows temporal change of these environments to be assessed. This is a pertinent
capability in the context of human modification of the nearshore environment
through coastal construction, beach nourishment, and land reclamation (Gares
et al. 2006).
5.3.4 Surrounding Environment
Examples of LiDAR topographic applications in the vicinity surrounding reefs
include regional mapping of changes along sandy coasts due to storms or longterm sedimentary processes (Guenther et al. 1996; Sallenger et al. 1999; Gutierrez
et al. 1998; Arens et al. 2002; Woolard and Colby 2002; Bonisteel et al. 2009;
Brock and Purkis 2009; Kempeneers et al. 2009; Klemas 2009). Beyond measuring seabed height, the laser return of a LiDAR also has the capacity to be used
to interrogate water quality (Babichenko and Poryvkina 1992; Kopilevich et al.
2005; Tuell et al. 2005). This is feasible because the quality and quantity of laser
light returned to the overflying instrument is altered by fluorescence, absorption,
and scattering within the water column. By quantifying these changes, Hoge
(2006) demonstrated that oceanic beam attenuation can be retrieved from airborne
laser-induced and depth-resolved colored dissolved organic matter (CDOM)
5 LiDAR Overview
133
unparalleled means of mathematically quantifying reef geomorphology.
While corals are the architects and builders, coral reefs are not, by any means,
made of corals alone. In fact, many other calcareous organisms, both animal and
plant, may contribute more to the volume of a reef than do the corals (Blanchon
et al. 1997; Wood 1999; Braithwaite et al. 2000; Perry et al. 2009). In near-shore
systems, there may also be considerable quantities of siliciclastic sediments within
the reef environment. Such settings are commonly termed ‘mixed’ carbonate
systems. As depicted in Fig. 5.7, the bedforms that these sediments create can be
appraised via bathymetric LiDAR. In the figure, reef features are easily discerned
in the IKONOS satellite imagery because they are spectrally different from the
surrounding substrate, as well as by LiDAR because they have considerable
topographic relief. By contrast, sedimentary bedforms are not spectrally distinct
and are unresolved by the satellite imagery, but visible by virtue of the differences
in relief observed in the LiDAR. This same figure demonstrates a further advantage of LiDAR over satellite imagery for reef mapping; in the southern portion of
the two images is an expansive reef complex, which due to depth cannot be seen
via IKONOS, but is intricately resolved in the LiDAR survey.
Naturally occurring bedforms include sediment waves, submerged aquatic
vegetation root masses, and obstruction scour and deposits. The structure of these
features can be related to factors such as sediment supply and grain size, as well as
serving as a useful proxy for wave, current, and tidal characteristics in the coastal
zone (the region depicted in Fig. 5.7 is clearly subjected to very rigorous tidal
currents). Furthermore, repeat coverage with time-separated LiDAR surveys
allows temporal change of these environments to be assessed. This is a pertinent
capability in the context of human modification of the nearshore environment
through coastal construction, beach nourishment, and land reclamation (Gares
et al. 2006).
5.3.4 Surrounding Environment
Examples of LiDAR topographic applications in the vicinity surrounding reefs
include regional mapping of changes along sandy coasts due to storms or longterm sedimentary processes (Guenther et al. 1996; Sallenger et al. 1999; Gutierrez
et al. 1998; Arens et al. 2002; Woolard and Colby 2002; Bonisteel et al. 2009;
Brock and Purkis 2009; Kempeneers et al. 2009; Klemas 2009). Beyond measuring seabed height, the laser return of a LiDAR also has the capacity to be used
to interrogate water quality (Babichenko and Poryvkina 1992; Kopilevich et al.
2005; Tuell et al. 2005). This is feasible because the quality and quantity of laser
light returned to the overflying instrument is altered by fluorescence, absorption,
and scattering within the water column. By quantifying these changes, Hoge
(2006) demonstrated that oceanic beam attenuation can be retrieved from airborne
laser-induced and depth-resolved colored dissolved organic matter (CDOM)
5 LiDAR Overview
133