Magnetometry Survey at Great Shoddesden

The geophysical survey was undertaken between 18th - 22nd October 2021 and 22nd - 24th August 2022. All geophysical survey work was carried out in accordance with recommended good practice specified in the EAC guideline documents published by Historic England (Schmidt et al. 2016) and the Chartered Institute for Archaeologists Standard and Guidance for archaeological geophysical survey (2014). The work on site conformed with the proposed methods set out in a Written Scheme of Investigation (WSI) submitted by AOC Archaeology group to Hampshire County Council, and which was approved by their Archaeologist David Hopkins, on the 18th of October 2021. Parameters and survey methods were selected that were suitable for the prospective aims of the survey and in accordance with recommended professional good practice (Schmidt et al. 2016). Digital photographs of every survey parcel were taken before, during and after geophysical survey to show any changes to field conditions following the programme of works. The photos were downloaded and stored off site. The gradiometer survey was carried out using a Bartington Non-Magnetic Cart. The cart system utilises two Grad-01 fluxgate gradiometer sensors mounted upon a carbon fibre frame, along with data logging equipment and batteries (see Appendix 2). Before each session of use, the cart system was balanced around a single set up point within the Site specifically chosen for being magnetically quiet. In balancing the machine around this point, it produces a more uniform dataset throughout and allows all data to be plotted with ease. Data was collected using zig-zag traverses alongside a constant stream of GPS data collected through a Trimble R10 GPS, enabling the collected data to be spatially georeferenced without the need for a pre-determined grid system. The data was collected through a laptop mounted to the cart using Geomar MLGrad601 software. A total of 25ha were surveyed using the Bartington cart. Care was taken to attempt to avoid metal obstacles present within the survey area, such as metal fencing around hedge boundaries as gradiometer survey is affected by 'above-ground noise' and avoiding these improves the overall data quality and results obtained. The data was downloaded from MLGrad601 and converted into a .xyz file in Geomar MultiGrad601before being processed along with the GPS data in TerraSurveyor v3.0.34.10. The details of these processed can be found in Appendices 2 and 3. Interpretations of the data were created in ArcGIS Pro and the technical terminology used to describe the identified features can be found in Appendix 4 The survey has succeeded in locating, recording and characterising surviving sub-surface remains within the Site, though more remains may be present that are not suitable for detection through magnetometry; The survey will help in determining the next stage of works as it has provided evidence that remains of an uncertain origin are most likely present on site, and has provided several targets for further investigation; It is not possible to provide an assessment of the potential significance of the identified remains in a local, regional or national context as it has not been possible to definitively characterise the nature of the anomalies identified through survey alone; The survey has resulted in a comprehensive report and archive.