Lateritic soil mapping of the Phrae basin, northern Thailand using satellite data

Landsat 7 Enhanced Thematic Mapper Plus image data was used to identify and map lateritic soil zones in the Phrae basin which is one of the largest intermountain basins in northern Thailand. The lateritic soil zones were discriminated using band ratio and principal component analysis. The lateritic soil detection images were processed by band ratio (band 3 / band 1), principal component analysis of bands 1 and 3, and principal component analysis of bands 1, 3, 4, and 5. The results of these three indices were superimposed using GIS to define a preliminary lateritic soil image of the study area. A threshold method was used for converting a grey scale image into a binary image. Different threshold values were used to find the most probable areas of lateritic soil zones in the image. The threshold values were determined from a published geological map and known lateritic soil areas with good exposure in the image. The quality of the results was evaluated by the normalized difference vegetation index. Field investigation was carried out to substantiate the remote sensing investigation and the laboratory GIS analysis. This method can also be applied to other lateritic soil and iron oxide regions.