Magnetic Signal Prospecting using Multiparameter Measurements: the Case Study of the Gallic Site of Levroux M. PE ¤ TRONILLE 1 * , J.THIESSON 1 , F.-X. SIMON 1,2 AND O. BUCHSENSCHUTZ 3 1 De¤ partement de ge¤ ophysique applique¤ e, UMR 7619 Sisyphe, Universite¤ Pierre etMarie CurieParis 6, 4 Place Jussieu, 75252 Paris cedex 05, France 2 Po“ le d’Arche¤ ologie Interde¤ partementalRhe¤ nan, Ope¤ rationsArche¤ ologiques, 2 Alle¤ eThomasEdison, ZA sud ^ CIRSUD, 67600 Se¤ lestat, France 3 UMR 8546 CNRS-ENS Arche¤ ologies d’Orient et d’Occident et textes anciens (AOROC), 45 rue d’Ulm, 75230 Paris cedex 05, France ABSTRACT The‘magnetic signal’ that combines both the induced (J i ) and the remanent (J r ) magnetization is widely used in archae- ological and pedological prospecting. Magnetic prospecting recording the lateral variations of the total magnetization is the most frequently used measurement before in-phase magnetic susceptibility (K ph ) and magnetic viscosity (K qu ) mapping. The work presented here brings together three types of prospecting technique: magnetic field survey and electromagnetic measurements with both frequency and time domain devices that measure magnetic susceptibility and viscosity respectively.The site studied, the Gallic town of Levroux (Indre,France), is particularly interesting because it includes features such as pits and ditches dug into the calcareous substratum partly filled with topsoil and with resi- dues of different metallurgical and fire activities.The field results indicated anomalies with different types of character- ization: (i) many compact features filled with magnetic, electrically conductive and minimally viscous materials; and (ii) elongated anomalies characterized by lower magnetic properties and electric conductivity but relatively higher magnetic viscosity than those of the compact features. In addition to the location of the features, the combination of the information brought by the different types of measurements allows us to evaluate the possible erosion of their upper parts by ploughing, to assess their depth (never deeper than 1.30 m) and to precise the nature of the feature’s fill. Copyright # 2010 John Wiley & Sons, Ltd. Key words: magnetic susceptibility; magneticviscosity; electromagneticinduction; magneticsignalmapping; metal- lurgical activity; Levroux Introduction The study of the magnetic properties of soils began 60 years ago with the work of Le Borgne (1955), who showed that soils have usually higher magnetic susceptibilities than their parent rock. This fact is at the origin of significant developments in archaeological prospecting (Aitken et al., 1958; Scollar et al., 1990) and different techniques using the magnetic properties of soils therefore have been developed. The magnetic method which records the lateral variations of the total magnetization (J) was firstly undertaken and showed its efficiency to locate buried features that were either heated, such as ovens and kilns, or unheated, such as pits and ditches (Aitken et al., 1958; Tite and Mullins, 1971; Mullins, 1974; Marmet, 2000; Benech et al., 2002). In parallel frequency-domain electromagnetic (FDEM) instru- ments began to be developed in the 1960s; they allow simultaneous measurement of both magnetic suscepti- bility (K ph ) and electrical conductivity (s) (Colani, 1966; Howell, 1968; Tabbagh, 1974; Tabbagh, 1986; Marmet, 2000; Benech et al., 2002). At the same time, time-domain electromagnetic (TDEM) instruments that measure decayed impulse response of the ground were proven to be sensitive to the loss or gain of Archaeological Prospection Archaeol. Prospect. 17, 141–150 (2010) Published online 5 August 2010 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/arp.384 * Correspondence to: M. Pe ´tronille, De ´partement de ge ´ophysique applique ´e, UMR 7619 Sisyphe, Universite ´ Pierre et Marie Curie Paris 6, 4 Place Jussieu, 75252 Paris cedex 05, France. E-mail: petronille@ipgp.jussieu.fr Copyright # 2010 John Wiley & Sons, Ltd. Received 19 March 2010 Accepted 30 June 2010