Forward modelling of magnetic anomalies in archaeological geophysics: A new software tool

Although magnetic methods are generally considered among the most important non–destructive techniques in Archaeology, in most cases their usage limits to the acquisiton of vertical gradient data and their direct interpretation in terms of walls or other archaeological features, often without the support of an accurate geophysical analysis. Disadvantages in the acquisition and direct archaeological interpretation of gradient data include the following issues: 1. In most cases the location of a buried artifact is laterally displaced with respect to the corresponding anomaly; 2. Important information about the physical properties of an object, which could have archaeological meaning, is ignored; 3. Information about the burial depth cannot be easily obtained; 4. Nearby objects generate complex anomalies (by the superposition principle) that cannot be interpreted by the simple visual inspection of gradient maps. Finally, Tabbagh (2003) showed that the reduction of anthropogenic disturbances and time variations of the geomagnetic field using appropriate filters gives better results compared to gradiometer measurements. Here we describe an approach to magnetic prospecting and analysis in Archaeology, which is based on the acquisition of total field data, their reduction to magnetic anomalies, and a computer–assisted analysis of the resulting data set. Our new software tool, ArchaeoMag, allows for the first time to reconstruct the geometry and magnetization pattern of a buried settlement through a trial–and–error procedure based on classical forward modelling algorithms. It also allows to determine whether an artifact has been burnt and eventually the approximate time of this event. In the next sections, we first review a method of acquisition and processing of magnetic data from an archaeological site. Then, we describe the operation of ArchaeoMag and the basic steps in forward modelling of archaeological anomalies. Finally, we will discuss the potentiality of this approach in difficult situations.