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S. Andréfouët
16.2 Direct Remote Sensing of Coral Reefs
In a coastal remote sensing context, habitats are often defined by a number of
attributes which generally include a geomorphological, a depth and a benthic description (Andréfouët et al. 2003). These attributes have been mapped with remote
sensing, afterwards leading to the study of habitat-related processes. This section
reviews Red Sea and Western Indian Ocean habitat mapping and functional studies
achieved through direct use of remote sensing.
16.2.1 Geomorphology
Modern geomorphology is the result of the convolution of a number of processes
acting at different time-scales (Camoin et al. 1997; Hopley 2011). A coral reef
geomorphological unit can be created by the combination of geological processes
occurring in the area, type of climate and weather forcing, variation of sea levels and
level of accretion and erosion due to the respective activity of dominant calcifying
communities (corals, coralline algae) and bioeroders. Once mapped, modern geomorphological features may bring clues pointing to the past geological events and
climate regime that have shaped the reefs present on the studied sites. For instance,
Purkis et al. (2010) have explained the occurrences in the Red Sea of karstic reticulated structures identified on high resolution Quickbird images by a Quaternary
signature of paleohumidity in the now hyperarid Red Sea.
Except for numerous past studies that have used aerial photographs (color and
black & white) to help geomorphological interpretation (e.g. Stoddart et al. 1971)
and Purkis et al. (2010), no other satellite borne geomorphological maps have been
directly used to infer the geological processes that have shaped coral reefs in the Red
Sea and Western Indian Ocean. Instead, remotely sensed geomorphological maps
have rather remained descriptive, as a first coarse layer of habitat description. For
instance, in the course of the Millennium Coral Reef Mapping project (Andréfouët et
al. 2006; Andréfouët 2011; Andréfouët et al. (2009) have compiled in one single atlas
geomorphological maps for Madagascar and every Western Indian Ocean Islands.
The maps were derived from Landsat 7 images at 30 m resolution. They depicted the
main coral reef geomorphological units down to approximately 25–30 m depth on
average (Fig. 16.2) following a hierarchical typology of units that is used globally.
The value of this work was to provide maps that were regionally consistent from
one country to another. Often, these maps yielded the first accurate inventory of the
surface area covered by coral reefs and associated lagoons, at national scale and per
individual island. These inventories are required to design national scale conservation
plans obeying international conservation targets (Wabnitz et al. 2010).
S. Andréfouët
16.2 Direct Remote Sensing of Coral Reefs
In a coastal remote sensing context, habitats are often defined by a number of
attributes which generally include a geomorphological, a depth and a benthic description (Andréfouët et al. 2003). These attributes have been mapped with remote
sensing, afterwards leading to the study of habitat-related processes. This section
reviews Red Sea and Western Indian Ocean habitat mapping and functional studies
achieved through direct use of remote sensing.
16.2.1 Geomorphology
Modern geomorphology is the result of the convolution of a number of processes
acting at different time-scales (Camoin et al. 1997; Hopley 2011). A coral reef
geomorphological unit can be created by the combination of geological processes
occurring in the area, type of climate and weather forcing, variation of sea levels and
level of accretion and erosion due to the respective activity of dominant calcifying
communities (corals, coralline algae) and bioeroders. Once mapped, modern geomorphological features may bring clues pointing to the past geological events and
climate regime that have shaped the reefs present on the studied sites. For instance,
Purkis et al. (2010) have explained the occurrences in the Red Sea of karstic reticulated structures identified on high resolution Quickbird images by a Quaternary
signature of paleohumidity in the now hyperarid Red Sea.
Except for numerous past studies that have used aerial photographs (color and
black & white) to help geomorphological interpretation (e.g. Stoddart et al. 1971)
and Purkis et al. (2010), no other satellite borne geomorphological maps have been
directly used to infer the geological processes that have shaped coral reefs in the Red
Sea and Western Indian Ocean. Instead, remotely sensed geomorphological maps
have rather remained descriptive, as a first coarse layer of habitat description. For
instance, in the course of the Millennium Coral Reef Mapping project (Andréfouët et
al. 2006; Andréfouët 2011; Andréfouët et al. (2009) have compiled in one single atlas
geomorphological maps for Madagascar and every Western Indian Ocean Islands.
The maps were derived from Landsat 7 images at 30 m resolution. They depicted the
main coral reef geomorphological units down to approximately 25–30 m depth on
average (Fig. 16.2) following a hierarchical typology of units that is used globally.
The value of this work was to provide maps that were regionally consistent from
one country to another. Often, these maps yielded the first accurate inventory of the
surface area covered by coral reefs and associated lagoons, at national scale and per
individual island. These inventories are required to design national scale conservation
plans obeying international conservation targets (Wabnitz et al. 2010).