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

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 (a) of multiple soil volumes at a test site. The shallow 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 a-data. Further comparisons were made between these datasets and aerial photography and field walking data. We found that the multiple EMI 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. Copyright (c) 2013 John Wiley & Sons, Ltd.