Geophysical Survey at Safeguarded Land at NWC, Cheltenham

The survey was undertaken using two types of fluxgate gradiometer sensors in both hand carried and all-terrain vehicle (ATV) towed configurations. Hand carried survey was undertaken using both Sensys and Bartington arrays. The Bartington system was composed of four Grad601 sensors mounted at 1m intervals (1m traverse interval) onto a rigid carrying 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 R12 Real Time Kinetic (RTK) differential Global Positioning System (dGPS) outputting in NMEA mode to ensure a high positional accuracy for each data point. MLGrad601 (Geomar Software Inc.) software was used to collect and export the data. Hand carried and cart-based ATV towed survey was undertaken using a five-sensor array deploying Sensys FGM650/10 sensors mounted at 1m intervals (1m traverse interval) onto a rigid frame. The system was programmed to take readings at a frequency of 100Hz (allowing for a 1-2cm 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 cart-based ATV system was linked to a Leica GS18 Real Time Kinetic (RTK) differential Global Positioning System (dGPS) and the hand carried system was linked to a Geode Real Time Kinetic (RTK) differential Global Positioning System (dGPS) outputting in NMEA mode to ensure a high positional accuracy for each data point. MonMX (Sensys Ltd) software was used to collect and export the data. Anomaly GeoSurvey v1.12.8 (Lichenstone Geoscience) and QGIS v.3.34.11 software was used to process and present the data respectively. A range of magnetic anomalies have been recorded by the survey. Most extensive are those indicative of ridge and furrow cultivation which is ubiquitous across the site. Other anomalies are due to natural variations in the overlying superficial deposits or are of modern anthropogenic origin being due to, or caused by, infilled ponds, service pipes, former boundaries, sections of field drains and modern cultivation. In addition, the survey has identified a cluster of anomalies of archaeological origin in the northern half of the site, which has been designated an area of archaeological activity based on the extensive and dense nature of the archaeological features recorded here. The anomalies are indicative of a series of ditches and enclosures aligned along a north-east to south-west axis which cover an area of approximately 5 hectares. Weaker anomalies of possible archaeological origin suggest the area of archaeological activity probably extends outwards from the obvious centre to the east, west and south of the main focus of activity. The concentration of archaeological activity identified by the survey on both the mudstone bedrock geology and the sand and gravel deposits indicates that there was likely sufficient magnetic contrast to assess the nature and extent of archaeological activity at the site. However, it is possible that results may be less reliable (in terms of resolving or identifying archaeological features) where alluvial deposits are present and/or in the south of the site in the areas of arable cultivation where ploughing may have degraded any archaeological features, if present. Nevertheless, it is considered likely that the results of the geophysical survey give a reasonably good indication of the extent of any likely archaeological activity. On this basis, and based solely on the results of the survey, the archaeological potential of the site is assessed as moderate to high in and around the defined area of archaeological activity in the north of the site and moderate to low in the southern part of the site.