Hill of Tara - Geophysical Survey
The geophysical component of the Discovery Programme’s Survey of the Hill of Tara is, to date, the largest (in terms of area coverage) such survey carried out in Ireland. Its success, combined with the celebrity of the site and the Discovery Programme’s policy of rapid and widespread dissemination of information has turned this work into something of a watershed for geophysical prospection in Irish archaeology.
Since the initial results of the Discovery Programme’s survey were first announced in late 1992, there has been an exponential increase in the use of geophysical techniques in both development sector and research archaeology and a parallel increase in the number of Irish firms and institutional units offering archaeogeophysical survey. The Discovery Programme is justifiably proud of its role as a catalyst in the development of this and other aspects of archaeological survey in Ireland because it measures its success not only in terms of how much it has contributed to the sum of archaeological data, but also what it can contribute to archaeological methodology, both practical and theoretical.
It is a policy of the Discovery Programme to foster and promote the development of the Irish archaeological infrastructure. In the case of the Tara Survey, which had an original projected life-span of less than one year, however, there was no option but to engage established, specialist archaeogeophysical contractors to carry out the work, and this meant going to Britain. In this respect, we are fortunate that Britain is home to some of the worlds’ leading experts in this field, experts who gave freely of their advice and for which we remain forever grateful. The archaeogeophysical strategy for the Tara survey was devised jointly by archaeologist and geophysicist.
In addition to using conventional geophysical imaging software we also developed a number of techniques in-house, utilising the powerful processing and imaging capabilities of ESRI ArcGIS. One such technique involves converting the geophysical data into a three-dimensional surface and manipulating it as one would a conventional terrain model. This proved to be the only way to reveal the resistivity signature of a very low-profile barrow to the north-east of Ráith Gráinne.