Trip report regarding remote sensing activities at ... - Up To - SOPAC

4.3 Zoning of the image
While processing the image, it appeared that 4 different
zones can be defined off it :
- the reef area,
- the closed lagoon area covering the submerged
delta,
- the mangrove area,
- the land area.
These zones of geological interest are much different, they
will be processed separately. To separate the zones, we
graphically contour them in interactive mode, using the forth
IVAS channel. Then, a mask is created overlaying each zone,
from which the areas are calculated.
5. Processing of the rectified and zoned image
Each zone is processed separately because of its
reflectance and of its distinct geologic interest.
5.1 Calculation of the transfer function
The choice of the mathematical function depends upon the type
of information we want to come up with. Therefore, we used the
following functions for processing the SPOT image of the Ba
River area :
- a linear upgrading function applied to areas,
in between limits or not, of the chosen zone;
- an exponential function applied inside the limits of
the histogramme peak, to upgrade preferentially the
high pixel luminance classes in the lagoon zone;
- a function of distribution of the pixel classes
(function of their luminance), which re-divides the
pixels in classes of equivalent number, called
equipopulation distribution.
More complex functions are also employed to determine
different ratings (see appendix II). The following ratings are
used to process the different zones.
- chromatic rating (Ref. 4), which is use to show the
turbidity of the water and the shallow lagoon bottom; -
vegetation rating (Ref. 5), for the mangrove zone;
- soil shining rating (Ref. 5), to differentiate bare soils
in the land and wetland zones.
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