Ground Penetrating Radar Survey at Campinglands Community Archaeology Project, Swaffham, Norfolk

Methodology 6.1. Data Collection 6.1.1. Geophysical survey comprised the ground penetrating radar method as described in the following table. 6.1.2. This method was selected because it's high-density resolution makes it effective for detecting very small, discrete features such as graves, structural remains and utilities. 6.1.3. Table of survey strategies: Method Instrument Traverse Interval Sample Interval Ground Penetrating Radar Mini Mira with a 400MHz Antenna 0.5m 0.05m 6.1.4. The radar equipment was set to sample every 0.05m along each line, controlled by the odometer wheel attached to the system. The odometer was distance calibrated at the start of the survey. 6.1.5. Traverse lines were separated by 0.5m and set out within a grid established using a Carlson BRx6 GNSS Smart Antenna RTK GPS, which is accurate to 0.008 m + 1 ppm in the horizontal and 0.015 m + 1 ppm in the vertical. 6.2. Data Processing 6.2.1. Data were processed in the commercial software package Geolitix. Processing steps were limited to: Time Zero Correction - The small lapse of time in which data was collected before the wave reached the ground level was removed. Amplitude Correction - A gain curve was automatically calculated by the software to account for signal attenuation with depth. The gain adjust will allow features at depth with a weaker signal to be resolved at the same plotting scale as near surface features. Dewow - A running mean value is calculated for each value of each trace and subtracted from the central point. This removes low frequency noise associated with antenna characteristics. Migration - The velocity value identified in the previous step was used to migrate the data. Migration forces the energy reflected by buried features back to their original position, allowing to correctly place the reflectors in space. 6.3. Data Visualisation and Interpretation 6.3.1. The individual GPR radargrams were stacked to form a three-dimensional cube of measurements. Greyscales were created by horizontally slicing the cube to produce plan-view 'timeslices'. These timeslices were initially considered in an animated GIF form, to analyse the three-dimensional extent of reflections. For print purposes, three gross soil volumes were considered: shallow, middle, and deep. The timeslices were also interpreted in combination with the radargrams, which visualise the form of the geophysical response, aiding anomaly interpretation. 6.3.2. The geophysical results have been interpreted in a layered environment, overlaid against open street mapping, satellite imagery, historical maps, LiDAR data, and soil and geology mapping. Google Earth (2022) was also consulted, to compare the results with recent land use. 6.3.3. Geodetic position of results - All vector and raster data have been projected into OSGB36 (ESPG27700) and can be provided upon request in ESRI Shapefile (.SHP) and Geotiff (.TIF) respectively. Figures are provided with raster and vector data projected against OS Open Data. 8. Conclusions 8.1. A ground penetrating radar survey has been successfully undertaken across the site. The survey was conducted to assess the subsurface archaeological potential of the site and to provide information for the next stage of archaeological investigation planned by the community archaeology project. The geology and environment has contributed to a good penetration of the radar signal. Modern interference was limited to extant features in the southwest of the survey area. 8.2. The main features detected in the survey area were the remains of a demolished building including its external and internal walls. The size, location and nature of reflections suggest it is the remains of the school building along with disturbed ground and rubble from its demolition. 8.3. Old footpaths, recorded on historical mapping, were also identified.