Visibility filtering of potential field data

The viewshed of a topographic dataset is the region around a given observation point that is visible from that<br>location. It has many uses, such as in urban environment planning, or in siting television and radio transmitters. The<br>viewshed is used here as a data enhancement tool to aid in the interpretation of geophysical potential field data. The<br>fraction of the area of a moving window visible from each point on the dataset (considered as if it were topography)<br>is computed. Since this area changes if the observer is raised above the surface, its vertical derivative can also be<br>computed. This derivative was found to be a useful method of enhancing subtle features, and is demonstrated on<br>aeromagnetic and gravity datasets from South Africa.