The Enhancement of Circular Features

F-20 THE ENHANCEMENT OF CIRCULAR FEATURES Abstract 1 Sunshading is a powerful tool for the enhancement of linear features in images and it is a standard tool used in the interpretation of geophysical potential field data. Given the azimuth and elevation of a source of illumination it calculates the reflectance from a surface composed of the data to be interpreted. Linear features lying at 90° to the illumination azimuth are enhanced while those that lie parallel to it become less apparent. The sunshading algorithm is here modified in two ways. Firstly its angular sensitivity to features of different azimuth from