Geology Reference
In-Depth Information
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(a)
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(b)
Fig. 12.
The analysed image around
the Murrawah and Al Gharbi banks
in Abu Dhabi. Al Gharbi, Fiyya and
Murrawah consist of a pre-Holocene
core with Holocene sediments around.
The islands are masked in both images,
deep-water pixels (blue band < digital
number 80) were masked in the clas-
sifi cation to avoid meaningless 'water
classes'. Uppermost image is the unpro-
cessed RGB Landsat image. Middle
image is the habitat classifi cation.
The lowermost image is the pseudo-
bathymetry derived from attenuation
in the Landsat image. The line across
the Murrawah bank shows the depth
profi le used in Fig. 14. Coral frame-
works (red) are mainly biostromal and
do not break the surface but are limited
to a depth range of 1.5-6 m. A series of
reticulate, biohermal stringer reefs that
almost reach the low tide water level
occur in the centre of the images.
(c)
is illustrated in Fig. 13b and shows vertices with
in- and outdegrees between 1 and 5, a frequency
of
d
= 1. We encountered a regular Markov chain.
Using the approach developed earlier in this
paper, little modifi cation was needed to change the
spatial matrix into a temporal transition matrix.
The spatial model was a regular Markov chain
with six vertices and
d
= 1. Translated into time,
this would assume reversibility of any process
and would suggest that these facies can all eas-
ily transit into each other, even take each other's
place depending on transition weightings. The
boundary to the deep-water facies that were not
evaluated because they were beyond the optical
resolution of the Landsat image, was coral. The
shallow boundary was formed by emergent sand.
All vertices (facies) had strong loops (trans-
itions to themselves, Fig. 13) suggesting that pix-
els in the image classes encoding these vertices
(facies) were most frequently adjacent to pixels of
the same class, i.e. they formed large, contiguous
patches with a high perimeter/volume ratio. It is
surmised that what is true in space may also be true
in time. Both coral and seagrass-algae can be rel-
atively stable on the short, ecological time-scale
operating in decades to few centuries. Transition
from coral into dense algae occurs when corals die
and are overgrown by algae. The coral die-back
