Comparing Apparent Magnetic Susceptibility Measurements of a Multi‐receiver EMI Sensor with Topsoil and Profile Magnetic Susceptibility Data over Weak Magnetic Anomalies

Abstract

Today, most surveys in archaeogeophysical prospection use magnetic properties to detect archaeological features. Such magnetic surveys are usually conducted with magnetometers and, to a lesser extent, with magnetic susceptibility meters and electromagnetic induction (EMI) sensors. Although the latter are the only instruments that allow mapping multiple physical soil properties simultaneously, EMI remains the odd-one-out in archaeogeophysical prospection. Nevertheless, by simultaneously recording the electric and magnetic soil variability, EMI survey can be beneficial in early archaeological evaluation stages, because detailed pedological and archaeological information is gathered at the same time. Furthermore, by using multi-receiver EMI instruments vertical soil variation also can be integrated into the survey. However, although the potential of EMI for mapping electric soil variations is well known from advances in soil science, magnetic susceptibility measurements have been investigated less. Here we show the potential of a multi-receiver EMI survey to detect weak magnetic anomalies by measuring the apparent magnetic susceptibility (κ a ) of multiple soil volumes at a test site. The shallow κ a data were compared with topsoil susceptibility measurements using a magnetic susceptibility loop sensor survey, and with magnetic susceptibility profiling using a probe sensor for evaluating the deeper κ a -data. Further comparisons were made between these datasets and aerial photography and field walking data. We found that the multiple EMI κ a measurements allowed for a straightforward discrimination of the natural and anthropogenic magnetic variations of shallow and deeper soil volumes, and allowed visualizing weak magnetic anomalies.

Demonstrating the contribution of dielectric permittivity to the in‐phase EMI response of soils: example from an archaeological site in Bahrain

“…; De Smedt et al . ). The response to susceptibility of the soil is linear, and the corresponding coefficients are provided in the second column of Table (at frequency and height ).…”

Combining multi‐receiver electromagnetic induction and stepped frequency ground penetrating radar for industrial site investigation

“…The ECa measurements for the 1PRP, 2PRP, 1HCP and 2HCP configurations are representative of soil volumes to depths of 0.5, 1.0, 1.6 and 3.2 m, respectively (Saey et al ., ). The MS a response for the PRP configurations is often unstable in field conditions (De Smedt et al ., ) and was disregarded in this study. For the HCP configurations, the MS a measurements correspond to soil volumes to depths of 1 and 1.5 m (De Smedt et al ., ).…”

“…The MS a response for the PRP configurations is often unstable in field conditions (De Smedt et al ., ) and was disregarded in this study. For the HCP configurations, the MS a measurements correspond to soil volumes to depths of 1 and 1.5 m (De Smedt et al ., ).…”

EMI as a non-invasive survey technique to account for the interaction between WW I relicts and the soil environment at the Western front

“…Strong relationships have been found between σ a and a variety of soil properties such as soil salinity, clay content, cation exchange capacity, exchangeable cations, clay mineralogy, moisture content and temperature (Rhoades et al, 1989;Sheets and Hendrickx, 1995;Doolittle and Brevik, 2014) while κ a proves to be mainly correlated with the amount of ferromagnetic oxides and the size of the magnetic grains (Dabas et al, 1992). Anthropogenic disturbances of the (top) soil, but also natural phenomena often cause local deviations of the magnetic susceptibility (Thiesson et al, 2009;De Smedt et al, 2014). Both σ a and κ a measurements at multiple coil configurations provide a complementary insight into the soil, by simultaneous mapping the anthropogenic and natural soil variations at multiple soil volumes, enabling an enhanced reconstruction of past human environments and their relationship with the landscape (Saey et al, 2013b).…”