Position and spatial orientation of magnetic bodies from archaeological magnetic surveys

Abstract

For the last twenty years magnetic surveys have frequently been applied in archaeological prospection. Among the different processing techniques that can be applied to the magnetic data, we studied the possibility for delineating the position and the spatial orientation of shallow depth magnetic anomalous bodies. The approach namely cross-correlation filter (or matched filter) has been adopted. At first, theoretical magnetic anomalies of total magnetic field, of its components and the vertical gradient of these, due to three-dimensional bodies, oriented S-N, E-W and NW-SE, were calculated. These synthetic bodies were considered a sum of many elementary prisms. Field measurements were simulated adding a noise component with different signal-to-noise ratio on the theoretical anomalies. In order to improve signal-to-noise ratio and to locate and delineate the orientation of the anomalous bodies a bidimensional cross-correlation technique was applied. Different synthetic anomalies, due to bodies with different dimensions, depths, susceptibility contrasts and geomagnetic parameters were used, as operators, to apply the cross-correlation technique. The efficiency of the method was improved using a normalised cross-correlation of the field data.