Comparison of geophysical techniques for investigating an in-filled ditch at Bury Walls hill fort, Shropshire

Five geophysical survey techniques were used to investigate the infilled section of the outer ditch at the Iron Age hill fort of Bury Walls, Shropshire. The techniques were resistance mapping and four profiling methods: resistivity sounding, ground-penetrating radar (GPR), P-wave seismic refraction and S-wave seismic refraction. The ditch was clearly visible on the resistance map and on GPR profiles, but no depth estimate was obtainable from these surveys. The most successful survey technique was S-wave seismic refraction, both for determining whether the ditch was present on a profile and for obtaining an estimate of its depth. A key factor for the success of S-wave seismic refraction profiling was that the ditch had been excavated into the sandstone bedrock