Transept Foundations of a 12th Century Chapel Revealed by Geophysical and Photogrammetric Prospection

Summary This study presents the work carried out at the Notre-Dame-du-Val chapel located in Sotteville-sur-Mer (Normandy, France). Local authorities are considering restoration work and have requested a geophysical survey of the surroundings. First, aerial photography by drone yields a Structure from Motion (SfM) model of the exterior of the chapel, completed by a 3D interior model. Geophysical prospecting consists in imaging shallow surface of surroundings, with help of Ground Penetrating Radar (GPR) and Electrical Resistivity Imaging (ERI). GPR measurements clearly reveal former apses on both sides of the chapel, corresponding to the transepts meets in perfect agreement with the presence of filled-in openings visible in the 3D interior photogrammetric model. The ERI measurements underline the presence of a very resistive substratum, probably corresponding to the local chalky formation where the chapel was built. Besides, resistive formation underlines the potential earthworks carried out to support the transepts meets, correlated with GPR signals. Several GPR and ERI anomalies have not been interpreted and deserve deeper investigation: archaeological excavations remains the only solution to confirm their nature. The restitution within the photogrammetric model allows a very explicit display of the results, integrating the architecture of the chapel and geophysical measurements.