At the beginning of December 2019, we carried out the second phase of our geophysical investigation of the scheduled site in Druitt Gardens, Christchurch. In August, we carried out a survey with ground-penetrating radar (GPR) in our search for geophysical evidence of the remains of the Saxon defences of the burh of Christchurch-Twynham. Archaeological evidence dating from the excavations of the 1970s predicted the continuation of the remains of a bank and ditch into and through the Gardens, but likely to be at some 2m below the present ground surface.
Previous geophysical surveys had used techniques which were unlikely to provide penetration of the soil to such depths and in this survey we had chosen techniques such as GPR and, in the present phase, resistivity imaging which are capable of penetration to 2m. The picture shows the resisitivity array laid out during the survey one of our longest lines of some 80m. The survey equipment automatically selects and combines various groups of 4 electrodes in a Wenner array of varying dimensions, and allows a resistivity profile through the soil to be imaged.
The August GPR results had identified a bank/ditch-like feature some 40m from the eastern end of our line. Initial results from the resistvity imaging seem to pick up this same feature, though we lack any sort of ground-truth to confirm the nature of this geophysical anomaly.