Automatic detection of circular outlines in regional gravity and aeromagnetic data in the search for impact structure candidates

A new automatic search algorithm based on circular data features has been applied to gravity and aeromagnetic regional data to detect impact structure candidates. Additionally, field investigations and laboratory analyses are needed to reach final conclusions. Compared to other Fennoscandian countries, the number of Norwegian impact structures is low such that the potential to find new ones should be high. This situation initiated the search for new impact structures in Finnmarksvidda (Northern Norway), an area of Precambrian basement rocks. Fresh impact craters are characterized by circular shapes, a pattern which also could be reflected in their geophysical potential fields. The presented algorithm calculates the amount of pixels in a given radius having a gradient direction towards a centre pixel. The algorithm differs from the commonly used circular Hough transform as it operates without an edge detection requirement. The algorithm detected a high number of features that were refined and reduced before field work by manual visual comparison to geologic and topographic maps.