Geophysical Survey at Druitt Gardens

Some members will be aware that for some time we have been negotiating with Historic England and Christchurch Town Council for permission to conduct a geophysical survey within Druitt Gardens and on the site the Scheduled Ancient Monument protecting the supposed known course of the Saxon defences of our ancient town.  We are grateful to the Town Council for providing funding for the survey and also to Historic England for granting us a Section 42 licence in response to our request to survey the SAM.  Although geophysical surveys have been carried out on site in the past, they did not reveal evidence of the defences and it is generally acknowledged that the techniques used were probably insufficient to reveal archaeological remains shown by excavations outside the Gardens during the 1970/1980s to be buried at depths approaching 2 metres.

The first part of our survey took place on 20/21 August 2019 under licence from the Town Council, and was carried out by Dr Richard Bates of St. Andrew’s University who was able to give us the benefit of his expertise and specialised equipment while in the area SAM_2402prior to taking part in an extensive survey at Stonehenge.  Dr. Bates used a MALA Ground Penetrating Radar (GPR) fitted with a 200 MHz antenna, a frequency which was aimed at providing depth penetration.  Initial results indicated that penetration to some 3m was being obtained.  We were very encouraged to see that on some lines interesting anomalies indicative of bank/trench -like features were apparent on the basic data plots which we hope to study with further processing and enhancement.  A view of the GPR in action is shown operating in the garden of Little Millhams in an attempt to see if any evidence of an eastern ditch to the town’s defences could be found.

SAM_2398In the time available, Dr. Bates was also able to deploy another deep-sensing piece of equipment. generally known as an EM31, or electromagnetic conductivity meter.  This equipment is shown in action on the left.  Also in the picture is the DGPS position-fixing equipment used by Dr. Bates, one component carried in a rucksack and the other component a fixed station on a tripod.  Use of this equipment provides simultaneous collection of geophysical and location data.

We hope and expect this to be the first part of a series of surveys with a variety of techniques over the currency of our six-month Section 42 licence.

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