What aerial photography reveals is a cropmark, the kind of ghostly outline that appears when buried features subtly affect the growth of whatever is planted above them, producing variations in colour and height that only become readable at altitude. In this case, the cropmark traces an enclosure roughly 35 metres across its longer axis and about 15 metres on the shorter, defined by what appears to be a fosse, or ditch, curving in a crescent shape.

The enclosure is not a standalone feature. It sits attached to the south-east of an existing rath, the kind of roughly circular earthwork that was commonly built across Ireland during the early medieval period, typically serving as a defended farmstead. This crescent-shaped addition functions as an annexe to that rath, a secondary enclosure appended to the main one. Such annexes are thought to have served practical purposes, perhaps corralling livestock or providing additional protected space outside the main enclosure. The feature at Knocknoran came to notice through digital aerial photographs taken in July 2006, which showed the cropmark with enough clarity to allow the enclosure's shape and approximate dimensions to be recorded.