The aerial reconnaissance at Krąplewo revealed a pattern of crop marks due to soil disturbance caused by human activity in the past. Due to their differentiated color it proved possible to recognize lithological disturbances indicative of a circular ditch of c. 31 m in diameter in addition to numerous irregular pits.
Accordingly, subsequent recognition of spatial structure of the site and its size was revealed by crop-marks. Their detection from the air makes possible to reveal different structures as all kind of disturbances under the surface are manifested in different features visible on the surface. Consequently, any permanent changes in the surface morphology made by people reflect today’s conditions of plan vegetation.
Aerial photographs of this archaeological site reveal two categories of marks. Within the ditch, the so-called positive crop-marks have been recorded. These were caused by organic matter originating from the moat. These kind of places usually keep moisture for some time making crops bigger and ripping later. At the same time, the occupation of the top of the hill on which the site was located, was recognized thanks to the so-called negative crop-marks and related to soil erosion and denudation processes. The resulting unfavorable conditions due to a shallow soil cover were reveled in the form of poor quality crops and early ripping.
A possibility of recording different crop-marks is caused by a range of factors, such as soil type, the year season, humidity balance, character and type of cultivation as well as time of the day in which the photo was taken. The successful outcome of the aerial reconnaissance at Krąplewo in 2008 was thanks to a combination of all these factors. The summer draught made possible to capture a significant differentiation of conditions affecting crop vegetation within a single field, which made possible to reveal a cone stronghold.