Series: Magnitude Surveys Ltd unpublished report series

Magnitude Surveys was commissioned to assess the subsurface archaeological potential of a c. 6ha area of land to the South of Woodrow Road, Melksham, Wiltshire. A fluxgate gradiometer survey was successfully completed across the survey area. The survey has primarily detected anomalies relating to historic agricultural activity, characterised by ploughing trends, drainage features and a former field boundary. Possible archaeological activity has been identified in the form of linear ditches, which could indicate earlier agricultural activity. Further linear, curvilinear and discrete anomalies were identified within the survey area; these could relate to agricultural use of the landscape, however, their origin is not clear in the magnetic data, therefore these anomalies have been classified as 'undetermined'. An area of extraction that is recorded on the historic mapping has also been identified. Anomalies of modern origin such as buried services, pylons and magnetic disturbance from associated overhead cables have also been detected.

Magnitude Surveys was commissioned to assess the archaeological landscape of a c. 1 ha area of land at Bromborough Court House, Bromborough, Merseyside. A full coverage combined cart-based fluxgate gradiometer and earth resistance survey was successfully completed. A number of anomalies with an undetermined, but potential archaeological origin have been identified. While these anomalies exhibit the potential to be archaeological in origin, due to the limited extent and context of the survey area, a specific archaeological origin for these anomalies cannot be confidently attributed. However, it is likely excavation work will confirm specific archaeological origins for some of these anomalies.

Magnitude Surveys was commissioned to assess the subsurface archaeological potential of two areas of land totalling c. 1.8 ha at Little Brickhill, Milton Keynes. A fluxgate gradiometer survey was successfully completed across the survey area; however, the narrow corridors forming the survey area have made interpreting anomalies more challenging. No anomalies suggestive of significant archaeological features were identified. The geophysical survey has primarily detected anomalies of an agricultural origin, in the form of possible ploughing regimes. Anomalies of an undetermined origin have also been identified across the survey area. Although they are likely to be of agricultural origin, an archaeological origin could not be ruled out. The impact of modern activity on the results is generally limited to the edges of the survey area in the northern area; a modern service is present within the southern area, producing haloes that further hindered interpretation.

Magnitude Surveys Ltd was commissioned to assess the subsurface archaeological potential of a c. 17.9ha area of land near Flixton, Suffolk. A fluxgate gradiometer survey was successfully completed across the majority of the survey area. The geophysical survey has primarily detected anomalies relating to agricultural practices, including drainage, cultivation, and both mapped and unmapped field boundaries. Variations within the background of the survey area relate to the near surface geology, which have in turn complicated a more confident interpretation of features and possibly obscured their full extent. Sources of interference relate to boundary features along the perimeter of the survey area as well as a modern service.

Magnetometer survey carried out over c. 57.5ha using hand-carried GNSS-positioned bespoke fluxgate gradiometer system. Magnitude Surveys was commissioned to assess the subsurface archaeological potential of a c.57.5ha area of land at Bucklesham Farm, Bucklesham, Suffolk. A fluxgate gradiometer survey was successfully completed across all but 0.7ha of the survey area and identified a multi-phase rectilinear field system, including some sharply angled junctions, at least one trackway and multiple enclosures, including several ring ditches, some of which correspond with visible cropmarks. These features are tentatively dated to later prehistory, or the Roman period based on their morphology, however it has not been possible to determine any relative phasing (though it is evident multiple phases are present). Additionally, the survey has detected further possible archaeological anomalies which have been interpreted as potential extensions of the identified field system as well as other possible field systems. Agricultural activity has been identified in the form of agricultural trends and field drains and historical field boundaries. Four extraction pits have been identified, relating to historical quarrying activity. Natural variations have been detected as broad anomalies and magnetic background enhancement attributed to the accumulation of superficial deposits. Modern interference is limited to the survey area perimeter.

Magnetometry survey carried out over 2.24ha using hand-carried GNSS-positioned bespoke fluxgate gradiometer system. Magnitude Surveys was commissioned to assess the subsurface archaeological potential of a c.2.24ha area of land at Darlington Crematorium, Darlington, County Durham. A fluxgate gradiometer survey was successfully completed across the site. No anomalies suggestive of significant archaeological features were identified. Anomalies related to historical agricultural use have been detected and interpreted as former field boundaries. The impact of modern activity on the results consists of ferrous ‘haloes’ caused by proximity to properties bordering the site and magnetic spread due to debris in the area at the time of survey. A series of pit-like and linear anomalies have been identified to the north-east of the survey area but are of undermined origin.

Magnetometer survey carried out over c. 17.7ha using quad-towed and hand-carried GNSS-positioned bespoke fluxgate gradiometer system. Magnitude Surveys Ltd was commissioned to assess the potential for sub-surface archaeological remains over a c. 17.7ha area of land northwest of Northwold, Norfolk. A fluxgate gradiometer survey was completed across most of the survey area, with areas totalling c. 1.54ha unable to be surveyed due to unsuitable ground conditions. The geophysical survey has detected a range of anomalies of agricultural origins, including mapped and unmapped former boundaries, pre-modern cultivation, drainage features and modern ploughing. Natural variations in the geology are visible across the survey area. Modern interference from field boundaries and telephone poles was present but minimal. Anomalies classified as ‘undetermined’ have also been identified but due to their weak signal their origin is unknown, although it is likely that they are of agricultural origin.

Magnetometer survey carried out over c. 23ha using hand-carried GNSS-positioned bespoke fluxgate gradiometer system. Magnitude Surveys was commissioned to assess the subsurface archaeological potential of a c. 23ha area of land at Ellesmere Road, Shrewsbury. A fluxgate gradiometer survey was successfully completed across the survey area. The geophysical survey has primarily detected evidence of the prolonged agricultural utilisation of the survey area, as well as anomalies of probable and possible archaeological origin. Archaeological activity has been identified in the form of strongly enhanced linear anomalies with orthogonal characteristics, none of which form complete enclosures. Anomalies related to historic agricultural use have been detected and interpreted as multiple ridge and furrow regimes and former field boundaries. Natural variations have been identified in areas of topographic change which suggests these broad anomalies are the result of colluvial processes. The impact of modern activity on the results is particularly evident at the perimeters of the fields, due to fencing, as well as in the form of a service line, demolition rubble from small out-buildings, and alignments of ferrous anomalies which may be indicative locations of former fence lines. A single anomaly has been classified as “Undetermined” where the origin is ambiguous from the magnetic results.

6. Methodology 6.1. Data Collection 6.1.1. Magnetometer surveys are generally the most cost effective and suitable geophysical technique for the detection of archaeology in England. Therefore, a magnetometer survey should be the preferred geophysical technique unless its use is precluded by any specific survey objectives or the site environment. For this site, no factors precluded the recommendation of a standard magnetometer survey. Geophysical survey therefore comprised the magnetic method as described in the following section. 6.1.2. Geophysical prospection comprised the magnetic method as described in the following table. 6.1.3. Table of survey strategies: Method Instrument Traverse Interval Sample Interval Magnetic Bartington Instruments Grad-13 Digital Three-Axis Gradiometer 1m 200Hz reprojected to 0.125m 6.1.4. The magnetic data were collected using MS’ bespoke hand-carried GNSS-positioned system]. 6.1.4.1. MS’ hand -carried system was comprised of Bartington Instruments Grad 13 Digital Three-Axis Gradiometers. Positional referencing was through a multi-channel, multi-constellation GNSS Smart Antenna RTK GPS outputting in NMEA mode to ensure high positional accuracy of collected measurements. The RTK GPS is accurate to 0.008m + 1ppm in the horizontal and 0.015m + 1ppm in the vertical. 6.1.4.2. Magnetic and GPS data were stored on an SD card within MS’ bespoke datalogger. The datalogger was continuously synced, via an in-field Wi-Fi unit, to servers within MS’ offices. This allowed for data collection, processing and visualisation to be monitored in real-time as fieldwork was ongoing. 6.1.4.3. A navigation system was integrated with the RTK GPS, which was used to guide the surveyor. Data were collected by traversing the survey area along the longest possible lines, ensuring efficient collection and processing. 6.2. Data Processing 6.2.1. Magnetic data were processed in bespoke in-house software produced by MS. Processing steps conform to the EAC and Historic England guidelines for ‘minimally enhanced data’ (see Section 3.8 in Schmidt et al., 2015: 33 and Section IV.2 in David et al., 2008: 11). Sensor Calibration – The sensors were calibrated using a bespoke in-house algorithm, which conforms to Olsen et al. (2003). Zero Median Traverse – The median of each sensor traverse is calculated within a specified range and subtracted from the collected data. This removes striping effects caused by small variations in sensor electronics. Projection to a Regular Grid – Data collected using RTK GPS positioning requires a uniform grid projection to visualise data. Data are rotated to best fit an orthogonal grid projection and are resampled onto the grid using an inverse distance-weighting algorithm. Interpolation to Square Pixels – Data are interpolated using a bicubic algorithm to increase the pixel density between sensor traverses. This produces images with square pixels for ease of visualisation. 6.3. Data Visualisation and Interpretation 6.3.1. This report presents the gradient of the sensors’ total field data as greyscale images (Figures 7, 10, 13, 16 & 19), as well as the total field data from the lower sensors (Figures 3 & 5). The gradient of the sensors minimises external interferences and reduces the blown-out responses from ferrous and other high contrast material. However, the contrast of weak or ephemeral anomalies can be reduced through the process of calculating the gradient. Consequently, some features can be clearer in the respective gradient or total field datasets. Multiple greyscale images of the gradient and total field at different plotting ranges have been used for data interpretation. Greyscale images should be viewed alongside the XY trace plot (Figures 9, 12, 15, 18 & 21). XY trace plots visualise the magnitude and form of the geophysical response, aiding anomaly interpretation. 6.3.2.

Magnetometer survey carried out over c. 6.65ha using hand-carried GNSS-positioned bespoke fluxgate gradiometer system. Magnitude Surveys was commissioned to assess the subsurface archaeological potential of a 6.65ha area of land at Old Wells Road, Shepton Mallet. A fluxgate gradiometer survey was successfully completed across the area, although a 0.67ha area was not surveyed due to lack of access. The geophysical data is characterised by anomalies relating to the historical agricultural utilisation of the survey area. This takes the form of a possible medieval strip field system, with ridge and furrow regimes that are contained within the system’s field boundaries. Further agricultural activity is evident across the survey area and has been detected as an infilled pond, a mapped former field boundary and drains. The impact of magnetic interference on the site is limited to field perimeters, caused by modern fencing and walls. Anomalies of undetermined origin have also been recorded.