Analysing potential field data using visibility

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