Near-surface temperature survey: An independent tool for delineation of buried archaeological targets

Abstract An essential principle of geophysical methods application at archaeological sites is difference of physical characteristics between the ancient remains and surrounding medium. Majority of archaeological objects – industrial, agricultural and weapon targets, cultural and worship pieces, many remains of ancient constructions, etc. – have contrast (comparing with the host media) thermal properties. Thus, temperature near-surface measurements (in small boreholes at the depth from several tens of centimeters up to several meters) can contain useful and sometimes unique information about the ancient objects occurring at some depths below the points of observations. At the same time, near-surface temperature survey is rarely carried out at archaeological sites. It was caused by a few reasons, most important from which is the noise induced by seasonal temperature variations propagating with some delay from the earth surface to the points of observations. Other disturbing factor is terrain relief effect significantly distorting the observed temperature field. Finally, analysis of temperature anomalies during the long time was limited by the absence of efficient quantitative procedures for temperature field examination. The developed interpretation scheme includes: (a) elimination of seasonal temperature variations by the use of linear filtering with utilization of repeated temperature observations and data of meteorological stations in the vicinity of the area under study, (b) calculation of terrain relief influence by a correlation technique, which facilitates the identification of anomalies associated with concealed geological features, (3) effective interpretation of temperature anomalies observed under complex environments. The last item is based on the essential similarities between the thermal and magnetic fields make it possible to apply to thermal prospecting improved modifications of characteristic points and tangents methods developed for magnetic prospecting. These methods are applicable to complicated environments: inclined relief, arbitrary magnetization (polarization), and an unknown level of the normal field. In order to classify the intensity of a thermal anomaly, it is suggested to use a “temperature moment”, equivalent to the “magnetic moment” used in the magnetic prospecting. The interpretation results were successfully tested both on models and in real situations.