SOIL TEXTURE DISCRIMINATION USING TMS/TM7 RATIO 
FOR BARE LIMITED VEGETATED AREAS. 
José da Silva Madeira Netto 
Laerte Guimaraes Ferreira Junior 
Marcel Pouget 
EMBRAPA/CPAC 
Depto. ARNSE 
Km 18 da BR-020 - Rod. BSB/Fortaleza 
73301-970 - Planaltina - DF, Brazil 
ISPRS Commission VII / Working Group 3 
ABSTRACT 
For tropical intense weathered soil, texture discrimination may be archived by slicing the Thematic 
mapper bands TM5 and TM7 ratio(TM5/TM7). The rationale behind this is that kaolinite and gibbsite, 
the dominant minerals in the clay fraction, present absorption bands in the TM7 spectral range, while in 
the TMS there are no important feature atribuble to the mineral constituents of these soils. So, soils with 
coaser texture (richer in quartz and iron concretions) tend to present smaller TMS/TM7 ratios than the 
finer ones (richer in kaolinite and gibbsite). However, vegetation cover of the land surface represent in 
general, an important constraint in the application of the ratio. 
In this work a procedure for reducing the effect of vegetative cover based on principal compensed 
transformation is employed. An area in Brasilia for which a good ground truth data is available, had 
images analysed for two dates: October 10, 1987, when large areas of exposed soil surface are after 
tillage operations as completed and September 20, 1990, prior soil preparation, when crop residues 
partially cover the soil. 
The results indicate the effectiveness of using the TM5/TM7 ratio for discriminating different textures 
and adequacy of principal compensed transformation for reducing the vegetation cover effects over this 
radio. 
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