Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

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Maria Kouli, Nikos Lydakis-Simantiris and Pantelis Soupios
Figure 6. 3,5,7 (R,G,B) Landsat-ETM color composite superimposed to the Digital Elevation Model of
the Keritis basin. Overlaid linear vector layer of the major lineaments is also shown with red color.
The seven resultant “primary map II” display for each pixel contamination index values
ranging between −1 and 1. This is close to the contamination index approach which is
calculated as the ratio between the measured concentration of a contaminant and the
prescribed maximum acceptable contaminant level (Melloul and Collin 1998; Praharaj et al.
2002; Babiker et al. 2005). However, the normalized difference index proposed by Babiker et
al. (2007) provides fixed upper and lower limits for the contamination level.
In a third step, the contamination index (primary map II) was rated between 1 and 10 to
generate the “rank map” using the following polynomial function which ranks the
contamination level (C) of every pixel between 1 and 10:
2
r = 0.5⋅
C + 4.5⋅
C + 5
where, C represents the contamination index value for each pixel and r represents the
corresponding rank value (Figure 7). After that, the relative weight (w) of each parameter has
to be calculated as the mean value (r: 1–10) of the corresponding rank map and the “mean r +
2” (r ≤ 8) for parameters that have potential health effects (e.g. nitrate) (Table 4).