Rapid 1D/3D inversion of shallow resistivity multipole data: Examples in archaeological prospection
Résumé
Fifteen years ago, the introduction of mobile multipole arrays led to substantial improvements in shallow electric prospection because it allowed information related to the vertical distribution of ground resistivity, in complement to the horizontal pattern of the detected features, to be extracted. However, to make full use of this wealth of information, further progress is needed to extend the qualitative interpretation of data to a more quantitative evaluation of the explored terrain. To that intent, we developed a two-step process: In the first step, a ID electric model is fitted to the data over the full explored area, and in the second step, using the moment method, localized 3D interpretation is applied to limited areas, for which the characteristics of a given feature require closer scrutiny. After a first test with synthetic data generated using the surface integral 3D modeling method, this process was applied to three different archaeological sites and one test site, for both handheld pole-pole array systems and a multipole continuous electric profiling mechanically pulled system. At the test site, the characteristics of a known wall were accurately recovered. At the Duntzenheim site, the thickness and width of the archaeological remains determined by 3D interpretation corresponded to the features observed through excavation. At the other two sites, 3D interpretation made it possible to establish that the conductive features extend across the full extent of the superficial resistive second layers.