Combining Photogrammetry and Subsurface Geophysics to Improve Historical Knowledge of Romanesque Churches in Normandy, France: Case Study of the Notre‐Dame‐du‐Val Chapel.

ABSTRACT This study presents the results of aerial and geophysical measurements carried out on the Notre‐Dame‐du‐Val chapel in Sotteville‐sur‐Mer (Normandy, France), a former leprosarium dating from the 15th century; the chapel is now deconsecrated and has been showing signs of ageing in recent years. Restoration work is planned, and geophysical investigations of the area around the chapel have been commissioned. In this article, we propose a robust methodology combining aerial and terrestrial measurements in the visible range with surface prospecting methods. Compiling all the measurements within a perfectly georeferenced 3D model allows the joint analysis of the results of different physical measurement methods to provide unexpected architectural and archaeological information. Photos were taken from the ground and using a drone to build photogrammetric models of the interior and exterior of the chapel. Ground‐penetrating radar (GPR) and electrical resistivity tomography (ERT) were the two survey methods deployed in the area surrounding the chapel. The geophysical measurements clearly reveal traces of apses—which have now disappeared—at the crossing of what would have been the building's transept, which match up with the filled‐in openings that are present. The existence of these apses can only be assumed from inside the chapel. The resistivity anomalies are perfectly correlated with the radar anomalies and allow new hypotheses to be formulated about the original structure of the chapel. Finally, mapping the local geology of the surroundings based on a geophysical survey provides crucial information about the history of the church's construction. Bringing this unknown architectural element to light and carrying out precise mapping of the local geology surrounding the chapel constitute a major breakthrough, as this will make it possible to improve our knowledge of the history of the chapel, in particular its origins, through research based on archaeological surveys. [ABSTRACT FROM AUTHOR]