1 Optimum Depth of Investigation and Conductivity Response Rejection of the Different Electromagnetic Devices Measuring Apparent Magnetic

ABSTRACT Electromagnetic susceptibility surveys are valuable for archaeological prospection owing to their ability to cover large areas of land. Their use, however, is often compromised by the conductivity influence of the soil and the limited investigation depth of the susceptibility response. To examine these constraints further, we compared the characteristics of two types of apparatus: coincident loop (e.g. Bartington MS2 field coil) and ‘Slingram ’ instruments (EM38, SH3, CS60 and CS150). Theoretical considerations suggest that in contrast to coincident loop apparatus, Slingram instruments are less influenced by the soil conductivity and offer a greater maximum depth of investigation. The experimental results presented in this paper collected over an artificial structure at the Centre de Recherches Géophysiques (CRG) of Garchy (France), confirm the theoretical results and indicate that Slingram instruments are preferable for field susceptibility measurements