Slingram frequency domain electromagnetic (FDEM) instruments allow simultaneous measurement of both magnetic susceptibility and electrical conductivity, which should justify their widespread use in archaeological surveying. However, this is not the case and their application remains quite limited due to: (i) a lack of knowledge about the role of coil orientation and spacing in terms of the detection abilities for archaeological features (especially for resistive bodies); and (ii) a lack of instrumentation specifically designed for shallow targets.We present here a test of a new version of the CS60 instrument (VCP coil configuration and 0.6 m intercoil spacing) for shallow depth resistive feature detection. This experiment was undertaken on the Roman site of Vieil-Evreux where a complete series of control resistivity and radar data was obtained. Detection of buried Roman walls was successful, in accordance with what can be expected from three-dimensional modelling.This confirms that the application of this type of instrument in archaeological surveys merits to be extended significantly.

Soil magnetic properties are significantly modified by pedogenesis and human activity; consequently their study is an important source of information about soil structure and history. In addition to measurements of magnetic susceptibility, now commonly practised, magnetic viscosity measurements can be undertaken as a routine survey method if well-matched instruments that are easy to use in the field and that offer a sufficient depth of investigation, exist.A theoretical study, supported by field tests of a prototype, demonstrates that a Slingram perpendicular coil configuration with a one-metre inter-coil spacing allows the required one-metre depth of investigation to be reached for both 1D and 3D models. The sensitivity of the instrument response to the viscosity is also very high over the whole measurement range (10µs to 1ms), while the sensitivity to electrical conductivity is reduced to a minimum.A first experiment at the Roman site of Vieil-Évreux illustrates how viscosity measurements can complement magnetic field and susceptibility measurements for a more accurate identification of an archaeological feature.

International audienceIf field applications of the electrostatic method are limited to roughly the first ten metres due to the necessity of staying in a low-induction number domain, the possibilities it opens in urban area surveying, dry hole resistivity logging, non-destructive testing and laboratory studies of the complex resistivity justify the design of a new multi-frequency resistivity meter presenting a very low-input capacitance and high-phase sensitivity. After a first series of sample measurements in the laboratory, the new resistivity meter was tested in two different field contexts: the mapping of building remains in a Gallo-Roman archaeological site under a flat meadow and the assessment of the thickness of anthropogenic layers in a town. The first test allowed a direct comparison with previous galvanic resistivity measurements and proved a very good agreement between the magnitude and spatial distribution of electrical resistivity. The second test established its reliable measuring abilities in a disturbed environment

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