Feature detection using sun shading

Sun shading is a powerful tool for the enhancement of linear features in images. Given the azimuth and elevation of a source of illumination it calculates the reflectance from a surface (which is composed of the data to be interpreted). Linear features lying at 90degrees to the illumination azimuth are enhanced, while those that lie parallel to it become less apparent. It is a standard tool used in the interpretation of geophysical potential field data. The sun shading algorithm is here modified in two ways. Firstly, its angular sensitivity to features of different azimuth from that being searched for is made an adjustable parameter, and secondly it is generalised to enhance features that lie either on or orthogonal to radius vectors that pass through a chosen origin position. The latter filter is particularly useful for the enhancement of circular anomalies, and is demonstrated on gravity data from South Africa. (C) 2003 Elsevier Science Ltd. All rights reserved.