It appears only under the right atmospheric conditions, when a buried outline causes the grass above it to grow differently from the surrounding pasture, producing what archaeologists call a cropmark. Aerial photography, rather than any ground-level survey, is what brought this earthwork to light at all.

The feature was identified through the Bruff aerial photographic survey, recorded as image AP 4/3689 in flight Bruff 183, which captured the site's rectilinear outline from above. Cropmarks form when buried features such as ditches, walls, or pits affect how plants grow in dry or stressed conditions; ditches tend to retain more moisture and produce lusher growth, while buried masonry can impede roots and cause patchier vegetation. The earthwork sits in improved, drained pasture that has been cut through by land drains and watercourses, which itself may have contributed to the feature's inconsistent visibility over time. Compiled by Alison McQueen and Vera Rahilly and uploaded to the record in September 2020, the site sits in close company with two other features: an enclosure roughly 50 metres to the south-east and a ring-barrow, a low circular burial mound of likely prehistoric date, about 110 metres to the north-west.

What makes the earthwork particularly slippery as a subject is its now-you-see-it, now-you-don't character in the aerial record. It was visible on an Ordnance Survey Ireland orthoimage captured between 2005 and 2012, but had vanished entirely from Digital Globe orthophotos taken between 2011 and 2013, and from a Google Earth image dated 28 June 2018. Ground conditions in any given season, including soil moisture levels and the state of the pasture, determine whether the cropmark shows at all. For anyone curious enough to visit the general area of Doonvullen Upper, the field itself offers little visual reward from ground level; the earthwork is, in a very literal sense, a feature that belongs to the sky.