I applied redness index to Landsat ETM+ in my study region located in the North western part of Algeria. I’ve got quite good results concerning Mediterranean red soil but I couldn’t understand why the vertisols are as bright as or even brighter than red soil in the redness index image.
Dear Kenneth and Dear Ram, Thank you so much for your help. But I have another point of view. Vertisols are the famous "black cotton soils" so ordinary they have a dark color (from the grayish or dark-red to the black). This color is due to the incorporation of organic matter in the clays.
These clays have swelling properties belong to the Smectites family mainly nontronites and Fe-beidellites. This means ferruginous clays with a high rate of Fe2O3. And I think that is the answer. The redness index values are high because of the ferruginous clays of the vertisols.
Welcome for a better explanation.
Dear All, take care to not confuse definitions.
Vertisol is a kind of soil according to WRB and Soil Taxonomy. They are characterised by vertic horizons where cracks occurs due to swellind and shrinking of the clay and where the amount of clay sould be higher than 30 %. Vertisols are commonly associated with sediments that have a high content of smectitic clays or that produce such clays upon post-depositional weathering.
Knowing that, what do you recognized in your image is not a vertisol, but a redness link to the meneralogy of the soil materia hihgkly corelated to the parent material (original rock).
@Lotfi Mustapha KAZI-TANI
Can u plz quote which band combination u have selected and formula?
Indeed Kenneth, even small amount of hematite can be important for soil color. The best exemple is the red mediterranean soils which contain no more that 3 to 7% of hematite but it plays an important role in pedogenesis and it could be exploited with remote sensing techniques.
@Sachin Patil
The redness index is calculated as follow:
RI=〖(B3)〗^2/((B1)*〖(B2)〗^3 )
B1 : Reflectance of band 1 corresponding to the blue
B2 : Reflectance band 2 corresponding to green
B3 : Reflectance band 3 corresponding to red
of Landsat ETM+
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