Geomorphological zonation - Distinguishing the different parts of a reef

To understand this page better, start with playing the game, where you get to know the different parts of a reef.

Geomorphological zones of a coral reef usually have distinct boundaries but are not easily recognizable on a simple satellite image.
A complex procedure has to be followed to visualize all these structures more clearly, so different classes of geomorphology can be determined.

Geomorphological classification includes:

the delineation of the geomorphological zones boundaries,
their visualization on a map,
together with a guiding classification scheme (or legend)

Let's explore what needs to be done to have a nice classification as result…

1^st ingredient = an original True Colour Composite (TCC)

Everything starts with a satellite image. The blue, green, and red spectral bands of this Landsat 7 ETM+ image will be the input data. These bands were selected as they contain most of the information concerning the submerged coral reefs.

True colour composite (composed by the blue, green and red spectral bands of a Landsat 7 ETM+ image). Source: Vanderstraeten, 2007.

2^nd ingredient = a bathymetric map

The differents parts of the reef (= geomorphological zones) we want to line off depend on depth. Therefore, a map which contains the topographical information of the seafloor (= bathymetric map) is needed.

Detail of a bathymetric map derived from a Landsat 7 ETM+ dataset. Source: Vanderstraeten, 2007.

Mix 1^st ingredient and 2^nd ingredient
= a Depth-improved Color Composite (DCC)

Now we have to merge together the spectral information (1^st ingredient) together with the topographical information (2^nd ingredient). The result of this composition is called a Depth-improved Color Composite.

DCC based on a Landsat 7 ETM+ dataset. Source: Vanderstraeten, 2007.

This DCC forms the base for the geomorphological mapping. When compared to a simple satellite image (ingredient 1), the advantage of integrating bathymetric information for the delineation of geomorphological zones is clearly noted.

Final result = geomorphological zonation

The different geomorphological zones can be integrated in a GIS and converted into a nice map.

Geomorphology zonation, derived from a Landsat 7 ETM+ image. Source: Vanderstraeten, 2007.

An additional scheme gives extra information on each of the different geomorphological classes:

Level 1	Level 2	Description
1. Land		As defined by the landmark
2. Patch reef		Relatively small coral formations with unclear morphology formed by hard corals or dead corals colonised by new organisms
	2.1. Dense patch reefs	Areas of agregated coral colonies where the corals cover more than 70% of the benthos
	2.2. Diffuse patch reefs	Areas of dispersed coral colonies where the corals cover less than 30% of the benthos
3. Reef crest		The shallowest and often emergent part of a reef, it seperates fore reef from back reef and lagoon
…	…	…