Joint inversion of EM and magnetic data for near‐surface studies

Abstract

Magnetic and electromagnetic measurements are influenced by magnetic susceptibility and, thus, are widely used in geophysical surveys for archeology or pedology. To date, the data inversion is performed separately. A filtering process incorporating both types of data is presented here. After testing the algorithm with synthetic data, the algorithm is used in several case studies in archeological prospecting. This approach presents two advantages: establishing the presence of remanent magnetizations (viscous or thermoremanent), and achieving more refined depth analysis of the anomaly.

Comparison between electromagnetic induction and fluxgate gradiometer measurements on the buried remains of a 17th century castle

“…In the present example the direct comparison of raw data is significant although the difference in anomaly location could be corrected by proper processing such as reduction-to-the pole (e.g. Tassis et al, 2008) or by transforming the EMI data (Benech et al, 2002). On the other hand, the gradiometer map was clearly sharper than the EM38DD maps; the anomaly borders were more abrupt.…”

Large-scale geophysical reconstruction of man-made ground at former industrial iron-furnace plantations

“…Previously, workers had inferred such a connection only for magnetic sources that are discrete, buried objects ͑e.g., Tabbagh, 1984Tabbagh, , 1986Tabbagh et al, 1988;Benech et al, 2002͒. Integrating the EM31 apparent-conductivity data ͑Figure 5c͒ with the ERT profiles ͑Figure 4͒ revealed that the sources of the conductivity anomalies around line S65 are mainly shallow. Excavation later revealed that the areas of high resistivity are caused by the presence of materials deposited by anthropogenic activity, such as charcoal and gravel, in particular, with some pockets of slag and disintegrated brick.…”

Slingram EMI prospection: Are vertical orientated devices a suitable solution in archaeological and pedological prospection?

“…This technique may also be used in magnetic susceptibility studies. It has a high potential: either in light weight systems easy to use in difficult field conditions or coupled with magnetic prospecting (Benech et al, 2002;Pétronille et al, 2010;Simpson et al, 2009b).…”