The discovery of a forgotten vault in the church of Sainte-Mesme (Les Yvelines)

A Ground-Penetrating Radar (GPR) prospection was carried out to sound the ground of the church of Sainte-Mesme, a village near Dourdan in France. This church was chosen because of the presence of a known underground vault in its south part. We tested the ability of determining the presence of a cavity from amplitude versus offset anomaly observed on multi-offset profile. During the acquisition, the GPR survey gave evidences of another forgotten underground vault in the main choir. Posterior to this discovery an archaeological study was performed in the opened vaults which concluded to the use of both underground rooms in the XIV^th century.