3D modeling and depth estimation in archaeological geophysics

Modern archaeological investigations are designed to gain maximum information whilst minimising damage to the archaeological site. Hence non-invasive surface studies are a key preliminary stage. One such technique is magnetometry which produces a surface grid of readings, each giving information about the whole 3D subsurface. The inversion of this convolution is an inverse problem requiring substantial regularisation. Current approaches incorporate prior information describing smoothness in a Bayesian setting. Typically the subsurface reconstruction is as a single layer, and requires various physical parameters, such as the depth and extent of the layer, to be known. In general, simultaneous estimation of depth and extent along with the magnetic susceptibility distribution is not possible without including further prior information – in particular about depth and extent. Here it is proposed that information about the stratigraphy is obtained from a separate technique where vertical cores of material are extracted from the site. This borehole data allows estimation of depth, extent and susceptibility at a small number of locations across the site. Resulting information can then be used in prior densities in the full subsurface reconstruction. Further, a multi-layer subsurface model is proposed which allows different depth and extent across the archaeological site. The approach is illustrated with part of a dataset from a real archaeological site for which excavation records are also available.