3. Data Collection and Processing

3.1 Gradiometry survey

The gradiometer survey covered an area of approximately 10 hectares (Figure 20) and was conducted using a Bartington Grad601-2 fluxgate gradiometer. A sample area was initially surveyed along traverses separated by 1m with 0.125m sample intervals, but this was found to provide insufficient detail. A limited area was surveyed at a very high sample resolution of 0.25 x 0.125m. However, the marginal amount of extra detail afforded by this resolution was not considered to outweigh the time required to complete the area, and so the full area within the ring fortress and adjacent areas on all sides were therefore surveyed with a sample density of 0.5 x 0.125m. On the southern side of the fortress some areas were not available for survey owing to the location of a manor house and related buildings. To the north and east of the fortress a limited number of additional grids outside the main area were surveyed for comparison, one of which is included on the data plot.

Figure 20 (left): Gradiometry data after applying zero mean traverse and destep processes. Data are presented with a grey-scale range of -2 to +3nT in order to maximise the visibility of archaeological detail. Comparison viewer requires Flash. [View Figure 20]. Comparison with Figure 10.

The gradiometer data were processed using Geoplot 3.0 and additional software written by Ben Urmston, before being exported to AutoCAD for interpretation. Data have been subjected to minimal correction processes: because of the zigzag collection strategy, it was necessary to apply a zero mean traverse process and to 'destep' grids. Figure 21 shows how the gradiometer data relate to the grid system of earlier excavations, the coordinate system of which is used here for ease of reference.

Figure 21 (left): Gradiometry data related to the grid system used in earlier excavations. Comparison viewer requires Flash. [View Figure 21]. Comparison with Figure 10.