Nevertheless, this sensor type is still not routinely used in geoarchaeological prospection English Heritage, Although both the electrical conductivity and the magnetic susceptibility measurement has been related to electrical resistivity and magnetometer measurements respectively Kvamme, , these relationships are not always straightforward Linford, The recent development of multiple coil instruments creates new opportunities for archaeological prospection Simpson et al.
Tabbagh, investigated the response of different coil orientations to layered-earth and three-dimensional objects with theoretical modeling for a 1. But an exhaustive study with different sensor configurations on field models was not conducted until now.
Our aim is to present different FDEM sensor measurements over an object with magnetic susceptibility contrast constructed in a test site, to evaluate the effect of the coil configuration. A fluxgate gradiometer survey was also conducted for comparison.
The soil consisted mainly of glacial till deposits of coarse sand with a minor fraction of poorly sorted stones. The magnetic susceptibility was fairly uniform over the test field, with higher values in the topsoil. Several objects were dug in to act as models for typical archaeological features, but here only one will be discussed. This object had a rectangular shape of 5 m in length, 0.
Figure 1: a Trench before filling up with basalt and topsoil. The length of the ruler is 0. The former instrument has two coil separations of 0. The latter sensor can measure two coil separations 1. The sensors were operated at 0. The in-line distance was maximally 0. Three criteria were used to evaluate the different sensor responses: absolute magnitude, compactness and changing direction resulting in positive and negative values.
