Magmetrometry Survey, Christchurch Solar Farm, Dorset - Geophysical Survey Report

The survey was undertaken using four Bartington Grad601 sensors mounted at 1m intervals (1m traverse interval) onto a rigid frame. The system was programmed to take readings at a frequency of 10Hz (allowing for a 10-15cm sample interval) on roaming traverses (swaths) 4m apart. These readings were stored on an external weatherproof laptop and later downloaded for processing and interpretation. The system was linked to a Trimble R8s Real Time Kinetic (RTK) differential Global Positioning System (dGPS) outputting in NMEA mode to ensure a high positional accuracy for each data point. MLGrad601 and MultiGrad601 (Geomar Software Inc.) software was used to collect and export the data. Terrasurveyor V3.0.37.0 (DWConsulting) software was used to process and present the data. Each full survey day, one traverse was surveyed twice, not in quick succession, to check calibration and demonstrate the repeatability of the results. The geophysical survey has recorded a range of anomalies against a variable magnetic background which reflects the heterogenous nature of the prevailing sand and gravel bedrock geology, superficial deposits, and soils across the proposed development area (PDA). Anomalies interpreted as of archaeological potential are largely confined to the higher north-eastern part of the PDA. Here a single rectilinear enclosure is identified, approximately 40m x 50m, located within a system of relict fields and possible trackways of uncertain date. None of the linear anomalies defining this likely former field system correlates with any of the temporary sub-divisions and boundaries, visible on satellite images, used when the site was used for pig rearing over the last two decades. Elsewhere former field boundaries and agricultural trends due to cultivation are recorded. A row of discrete anomalies, possibly indicative of burning, may locate a row of burned-out tree stumps parallel with and immediately adjacent to a 19th century boundary, now removed, are also recorded.