Facies discrimination in laterites using Landsat Thematic Mapper, ASTER and ALI data—examples from Eritrea and Arabia

Lateritic palaeosols cover roughly 33% of Earth's land surface. In spite of this, laterite facies remain largely unmapped. This paper illustrates how spectral properties of clays and iron minerals guide the mapping of three laterite facies using remote sensing. Remotely sensed data and image processing techniques prove ideal for effective mapping of laterites over large areas and difficult terrain so that their economic importance can be evaluated. Several types of remote sensing data are considered and the most appropriate selected. A 700 km2 area in Eritrea is used as a test site. A laterite facies map derived from remotely sensed data is presented for the first time. Methods of mapping are given using Landsat Thematic Mapper (TM), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Advanced Land Imager (ALI) data. Field evidence supports observations. Remote sensing methodology developed for the test site is applied to unvisited areas in Eritrea and Saudi Arabia. The results indicate that laterite facies maps can be produced easily and used to assess: ground water quality; viable agricultural land; areas prone to landslide; building resources, and potential base metal and gold mineralisation sites. Mapping laterite distribution in relation to topography also sheds light on the tectonic evolution of NE Africa, whilst the presence of laterites gives clues to ancient terrestrial climate.