Magnetism and Archaeology: Three-component Magnetometers for Ground and Drone Surveys and Integrated Approach for Advances in Archaeological and Geophysical Research

Magnetic surveying is nowadays quite commonly used as a tool for imaging the near-surface in archaeology. Different devices and measurement strategies exist, each with different advantages and limits. Most of the time, surveys are conducted with vertical-component or total-field gradiometers to produce a pseudo-gradient magnetic map. Total field measurements using scalar magnetometers can also be conducted, albeit less frequently, to produce magnetic anomalies maps. In both cases, maps are visually interpreted and can provide precious information to guide archaeological excavations.

It is proposed here to go further than the tool-oriented approach trough a better integration between geophysical and archaeological sciences. Advances in metrology and quantitative interpretative potential-field methods can help the archaeological interpretation and results from excavations can help to better constrain 3D magnetization models and quantitative methods.

Results obtained through such an approach are illustrated by two examples. Firstly, the conception of a device using three-component fluxgate magnetometers that allows to compensate for the magnetic influence of the carrier. Due to its lightweight (less than 200 grams including their electronics), such device can easily be fixed on a drone while ensuring the compensation of its magnetic field. Such equipment enlarges the possibilities of application in archaeological contexts by allowing multi-sensor measurement as well as fast drone-borne surveys. Secondly, The application on the site of Qasr 'Allam in Egypt which allowed 1) to identify, map and date one of the oldest irrigation channel system known in the Sahara and 2) to revise a depth inversion method from total-field magnetic data by introducing a form factor in the 2D analytic signal.