Geophysical Methods

Abstract

Geophysical methods can measure various physical properties of the subsurface soils and rocks. Such properties are not only shaped by geophysical processes but they can also reflect alterations caused by humans. Prospecting methods were originally designed to measure geophysical features at the scale of several metres or kilometres, while archaeological features are of interest at the scale of centimetres or a few metres, at most. Thus, some methods are readily adapted to archaeological sites, while others are of marginal or negligible value. Geophysical methods provide raw data which must then be processed and evaluated. The first step is to present the data in a form which can be understand by archaeologists, either by constructing a model of the physical phenomena thought to be responsible and changing this until the measured data are accounted for within a minimum error, or by using information which provide some degree of separation of the components of the measurements which are due to archaeological sources from those of natural or modern origin. Usually, the geophysical methods are classified into two main groups of passive and active methods. Within the first group, the amplitude of nearly steady magnetic, gravitational and electrical perturbation fields, generated by buried features, are measured at the sensing device. In the second group, artificial seismic, electrical and electromagnetic (inductive and impulsive) signals are emitted by the device, which then senses the return signals, more or less altered by the typical responses of the subsurface features.