In this article we assess the abilities of a new electromagnetic (EM) system, the CMD Mini-Explorer, for prospecting of archaeological features in Ireland and the UK. The Mini-Explorer is an EM probe which is primarily aimed at the environmental/geological prospecting market for the detection of pipes and geology. It has long been evident from the use of other EM devices that such an instrument might be suitable for shallow soil studies and applicable for archaeological prospecting. Of particular interest for the archaeological surveyor is the fact that the Mini-Explorer simultaneously obtains both quadrature ('conductivity') and in-phase (relative to 'magnetic susceptibility') data from three depth levels. As the maximum depth range is probably about 1.5 m, a comprehensive analysis of the subsoil within that range is possible. As with all EM devices the measurements require no contact with the ground, thereby negating the problem of high contact resistance that often besets earth resistance data during dry spells. The use of the CMD Mini-Explorer at a number of sites has demonstrated that it has the potential to detect a range of archaeological features and produces high-quality data that are comparable in quality to those obtained from standard earth resistance and magnetometer techniques. In theory the ability to measure two phenomena at three depths suggests that this type of instrument could reduce the number of poor outcomes that are the result of single measurement surveys. The high success rate reported here in the identification of buried archaeology using a multi-depth device that responds to the two most commonly mapped geophysical phenomena has implications for evaluation style surveys.
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This paper presents the results of geophysical surveys conducted within two castles in central Iberia: the fortifications of Molina de Aragón and Atienza, both located within the modern province of Guadalajara in Spain. They represent essential case studies for understanding the transformations of the frontier societies of medieval south‐western Europe, because both were founded during the Andalusi period, both played a fundamental role at the time of the military confrontations between opposing Islamic and Christian states, and both became capitals within the feudal dependencies of the Crown of Castile during the Late Middle Ages. At present, these castles are uninhabited and protected archaeological sites, with no modern developments within their wards; the adjacent towns have developed on the outskirts of their outer walls. Although both castles have been the focus of uneven amounts of archaeological research, geophysical surveys, the first conducted at these sites, have proved to be a fundamental tool not only for planning future archaeological investigations but also for the data that they have provided on the potential roles of these castle wards.
Several studies have suggested the potential value in applying gamma radiation surveys to support identification of buried archaeological features. However, the number of previous studies is very small and has yielded mixed results. The true efficacy of the technique is therefore unclear. Here, we report on an alternative survey method that uses Groundhog®, a portable gamma radiation system with spectrometric capability, to achieve high spatial density monitoring of archaeological sites. The system, which is used extensively in the nuclear industry, was used to carry out preliminary surveys at four different locations within the Silchester Roman Town. Targeting a site for which an extensive amount of archaeological data is available facilitated testing of the method on a range of known target types. Surveys were carried out along 1‐m transects at an approximate walking speed of 1 m per second, resulting in the capture of one radiation measurement per square metre. Total gamma radiation, recorded in counts per second, was presented in the form of surface radiation (contour) maps and compared against existing geophysical data. Total gamma counting consists of counting gamma rays, without energy discrimination, that are spontaneously emitted by the material under investigation. The obtained counts represent the total, or gross, gamma contribution from all radionuclides, both natural background series and anthropogenic. Radiation anomalies were identified in two of the four survey sites. These anomalies correlated with features present in the geophysical data and can be attributed to a Temenos wall bounding the temple complex and an infilled clay pit. Early results suggest that this may be a complementary technique to existing geophysical methods to aid characterization of archaeological sites. However, it is believed that data quality could be significantly improved by further increasing spatial resolution. This will be explored as part of future fieldwork.
The aim of processing and subsequent visualization of magnetometer data is to provide both the specialist and non‐specialist with a dataset that can inform decision‐making and subsequent risk management in a sensible and appropriate way. Magnetometer data are complex, and require careful processing and thoughtful visualization to transform them from a stream of measured values into a clear, interpretable dataset. Key generic processing routines are introduced which deal with noise reduction and enhancement of magnetic anomalies, to improve the visual appearance and positioning of data. Common visualization approaches of processed data are also highlighted.
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