Studies of the terrain to select route locations and sites for detailed geotechnical investigations are essential preliminaries to highway survey and design. The process of using all sources of information, including remote sensing, to derive an understanding of the engineering characteristics of an area is known as terrain evaluation. The basis of terrain evaluation is terrain classification, an effective form of which utilises landform analysis. There are strong links between landform patterns as seen at the surface and the underlaying geology, soils and moisture regime. These patterns may easily be mapped from aerial photographs or satellite images and the terrain classification that results is appropriate for planning preliminary ground surveys. The classification can be used to predict where changes in soil conditions occur and to relate individual samples to the overall project. The two most useful forms of remote sensing are aerial photographs for detailed work and landsat imagery for regional studies. Panchromatic photography is available in many parts of the world and there is increasing experience in its use in the tropics. If more detailed photography using special films is required, the use of a light aircraft carrying small format cameras can provide high quality photography at low cost. Landsat imagery has proved useful for preliminary surveys where interpretation of photographic prints of imagery can provide a terrain classification. More detailed analysis can be made with a computer, preferably using an interactive processor, and the use of these systems will probably increase as their cost decreases. The use of terrain evaluation is illustrated by examples from Africa and Asia. (Author/publisher)
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