Ground Penetrating Radar Survey, All Saint’s Church, Brixworth Surveyed by Sarah Semple and Alex Turner Report by Alex Turner November 2010 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Table of Contents Table of Contents .................................................................................................................................. 2 Table of Figures ..................................................................................................................................... 2 Introduction ........................................................................................................................................... 4 Survey location ...................................................................................................................................... 4 Survey methods ..................................................................................................................................... 4 Data Presentation .................................................................................................................................. 4 Data Processing ..................................................................................................................................... 5 Results and Interpretation ................................................................................................................... 5 Area 1 .................................................................................................................................................. 6 Area 2 .................................................................................................................................................. 6 Area 3 .................................................................................................................................................. 6 Area 4 .................................................................................................................................................. 6 Area 5 .................................................................................................................................................. 7 Area 6 .................................................................................................................................................. 7 Area 7 .................................................................................................................................................. 8 Resistivity Survey – Results and Interpretation ............................................................................... 8 Plots of Results ‐ Areas 1‐7 4.59ns‐ 49.46ns ..................................................................................... 20 Plot of GPR Results (4.59ns – 49.46ns) with excavation plans overlaid ...................................... 31 Interpretation of the GPR plots – 4.59ns – 49.46ns ......................................................................... 42 References ............................................................................................................................................ 53 Table of Figures Figure 1 ‐ Location of the GPR surveys ................................................................................................. 9 Figure 2 ‐ Location of resistivity survey showing overlap with GPR surveys ............................... 10 Figure 3 ‐ Location of GPR survey traverses ....................................................................................... 11 Figure 4 ‐ Ground plan illustrating position of pier base in the chancel ........................................ 12 Figure 5 ‐ Area 2 interference from electrical services ....................................................................... 12 Figure 6 ‐ Area 3 Transect 5 (velocity 0.075 m/ns) .............................................................................. 13 Figure 7 ‐ Ordnance Survey (1:2500) 1st Revision, 1900 overlaying the GPR plots ....................... 14 Figure 8 ‐ Area 6 Transect 1 ‐ showing feature [6.4] ........................................................................... 15 Figure 9 ‐ Area 7, transects 2 and 12, XZ trace profiles ...................................................................... 16 Figure 10 ‐ Results of the resistivity survey ........................................................................................ 17 Figure 11 ‐ Interpretation of resistivity survey ................................................................................... 18 Figure 12‐ Ordnance Survey (1:2500) 1st revision 1900 overlaying the resistivity plot ................ 19 Figure 13 ‐ Plot of GPR results 4.59ns (velocity 0.075m/ns) depth ~ 0.17m .................................... 21 Figure 14 ‐ Plot of GPR results 9.09ns (velocity 0.075m/ns) depth ~ 0.34m .................................... 21 Figure 15 ‐ Plot of GPR results 13.47ns (velocity 0.075m/ns) depth ~ 0.50m .................................. 22 Figure 16 ‐ Plot of GPR results 18.06ns (velocity 0.075m/ns) depth ~ 0.68m .................................. 23 2 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 17 ‐ Plot of GPR results 22.51ns (velocity 0.075m/ns) depth ~ 0.84m .................................. 24 Figure 18 ‐ Plot of GPR results 27.09ns (velocity 0.075m/ns) depth ~ 1.02m .................................. 25 Figure 19 ‐ Plot of GPR results 31.54ns (velocity 0.075m/ns) depth ~ 1.18m .................................. 26 Figure 20 ‐ Plot of GPR results 36.12ns (velocity 0.075m/ns) depth ~ 1.35m .................................. 27 Figure 21 ‐ Plot of GPR results 40.57ns (velocity 0.075m/ns) depth ~ 1.52m .................................. 28 Figure 22 ‐ Plot of GPR results 45.01ns (velocity 0.075m/ns) depth ~ 1.68m .................................. 29 Figure 23 ‐ Plot of GPR results 49.46ns (velocity 0.075m/ns) depth ~ 1.85m .................................. 30 Figure 24 ‐ Excavation plans and GPR results 4.59ns (velocity 0.075m/ns) depth ~ 0.17m .......... 31 Figure 25 ‐ Excavation plans and GPR results 9.09ns (velocity 0.075m/ns) depth ~ 0.34m .......... 32 Figure 26 ‐ Excavation plans and GPR 13.47ns (velocity 0.075m/ns) depth ~ 0.50m ..................... 33 Figure 27 ‐ Excavation plans and GPR results 18.06ns (velocity 0.075m/ns) depth ~ 0.68m ........ 34 Figure 28 ‐ Excavation plans and GPR results 22.51ns (velocity 0.075m/ns) depth ~ 0.84m ........ 35 Figure 29 ‐ Excavation plans and GPR results 27.09ns (velocity 0.075m/ns) depth ~ 1.02m ........ 36 Figure 30 ‐ Excavation plans and GPR results 31.54ns (velocity 0.075m/ns) depth ~ 1.18m ........ 37 Figure 31 ‐ Excavation plans and GPR results 36.12ns (velocity 0.075m/ns) depth ~ 1.35m ........ 38 Figure 32 ‐ Excavation plans and GPR results 40.57ns (velocity 0.075m/ns) depth ~ 1.52m ........ 39 Figure 33 ‐ Excavation plans and GPR results 45.01ns (velocity 0.075m/ns) depth ~ 1.68m ........ 40 Figure 34 ‐ Excavation plans and GPR results 49.46ns (velocity 0.075m/ns) depth ~ 1.85m ........ 41 Figure 35 ‐ Interpretation of GPR ‐ 4.59 ns ~ 0.15 metres .................................................................. 42 Figure 36 ‐ Interpretation of GPR ‐ 9.09 ns ~ 0.34 metres .................................................................. 43 Figure 37 ‐ Interpretation of GPR ‐ 13.47 ns ~ 0.50 metres ................................................................ 44 Figure 38 ‐ Interpretation of GPR ‐ 18.06 ns ~ 0.68 metres ................................................................ 45 Figure 39 ‐ Interpretation of GPR ‐ 22.51 ns ~ 0.84 metres ................................................................ 46 Figure 40 ‐ Interpretation of GPR ‐ 27.09 ns ~ 1.02 metres ................................................................ 47 Figure 41 ‐ Interpretation of GPR ‐ 31.54 ns ~ 1.18 metres ................................................................ 48 Figure 42 ‐ Interpretation of GPR ‐ 36.12 ns ~ 1.35 metres ................................................................ 49 Figure 43 ‐ Interpretation of GPR ‐ 40.57 ns ~ 1.52 metres ................................................................ 50 Figure 44 ‐ Interpretation of GPR ‐ 45.01 ns ~ 1.68 metres ................................................................ 51 Figure 45 ‐ Interpretation of GPR ‐ 49.46 ns ~ 1.85 metres ................................................................ 52 3 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Introduction A Ground Penetrating Radar (GPR) survey was carried out at All Saint’s Church, Brixworth at the request of the Brixworth Archaeological Committee in order to assess the sub‐surface survival of archaeological evidence associated with the church and earlier monastic settlement. Good archaeological evidence from previous excavations allows a detailed picture of a range of buildings, particularly to the north of the church, but the full geographic extent of the monastic structures remains unknown. Additional work within the available floor space inside the church was also undertaken in an effort to detect earlier foundations. The application of GPR as a non‐intrusive survey method follows on from an earlier electrical resistance survey, undertaken by Arnold Aspinall, and presented here alongside the GPR results. Survey location Seven areas were surveyed, three outside and four inside the church (Figure 1). The location of areas [1], [2] [3] and [7], within the internal space of the church, was largely constrained by physical access to sufficient areas of clear floor surface. The location of the external surveys areas was partly dictated by the density of funerary monuments within certain parts of the graveyard and the location of earlier features shown on the plans from earlier excavations. The area north of [4], whilst it was considered a good target for survey, was too uneven and the grass too long for the successful deployment of GPR. The presence of electrical conduits for the external lights and internal sockets also limited the areas that could be surveyed. Figure 5 is a good example of the interference to the electro‐magnetic GPR signal from live electrical circuits. The relocation of the electrical resistance survey was derived from a combination of its alignment with permanent grid markers [B] and [C] and the position of paths shown on both the modern and historic Ordnance Survey maps (Figures 2 and 12). Survey methods The external survey areas were laid out using tapes and aligned to the permanent grid markers [B] and [C]. Internal survey areas within the church were referenced to locatable architectural features shown on the available plan of the building. The external GPR survey was carried out using a Mala RAMAC X3M equipped with a XV11 monitor and a 500 MHz antenna. Parallel traverses were surveyed at one metre intervals using perpendicular traverses to two parallel tapes orientated east‐west on the survey grid and trace readings were taken along each traverse at 0.05 metre intervals. The GPR equipment was mounted on a rough terrain cart and trace measurement was controlled by the onboard calibrated measuring wheel. The internal survey utilised the same equipment but the antenna used a smaller distance measurement wheel attached directly to the case and was dragged rather than attached to the rough terrain cart. In order to obtain more readily interpretable results from the restricted survey area available, a more intensive survey strategy was adopted. To act as a control for the rest of the survey areas, Area [1] was surveyed using the time consuming Mala grid‐survey mode. This consists of two sets of perpendicular transects resulting in an effective survey interval of 0.05 metres in both the X and Y directions. Areas [2], [3] and [7] were surveyed using parallel traverses spaced 0.3 metres apart with traces taken at 0.01 metre intervals. Data Presentation Upon completion of the survey, the geophysical data was transferred from the portable computer to a desktop PC and processed using Reflexw, Reflex3Dscan, a proprietary program 4 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth written for data translation, Microsoft Access, Surfer 9.0 and ArcGIS 9.3.1. Ordnance Survey Mastermap data was used to locate the survey results and produce the basic GPR plots. A further detailed digital plan of the church and excavations was provided by Christina Unwin in Adobe Illustrator format and this allowed the direct overlay of the excavation results on the geophysical images. All final illustrations were compiled in Adobe Illustrator. Calculation of signal velocity was undertaken using estimation from hyperbolic diffraction tails. The determination of signal velocity is an important factor in the determination of the depth of features and clearly showed that using a generalised velocity based on the local geology was too imprecise and significantly overestimated the depth of signal penetration. As with all GPR survey the computation of depth is reliant on an understanding of the velocity of the electro‐
magnetic signal through the material being surveyed. Since GPR signal attenuation is greater in soils with a high conductivity (Linford 2006, 2236), the success of the GPR methodology was partly dependant on the amount of electro‐magnetic signal attenuation experienced. The sub‐
surface water content is a major factor in GPR response and the seasonal timing of the survey was an important element in the acquisition of good data. Data Processing The data was processed in ReflexW using the following inbuilt 2D processing tools: Subtract‐mean (dewow). The running mean value, for thevalue of each trace, is subtracted from the central point. For the data presented here a time window of 2ns was used for the calculation of the running mean value. This filter compensates for the bow in the base level of the signal caused by the close proximity of the GPR receiver and transmitter. The low‐frequency time‐
varying component is removed by the application of a high‐loss temporal filter to the detected signal (Annan 2009, 34). Static Correction: A negative static correction of 6ns was applied to the data. The effect of this shift was to shift the time upward for each trace towards smaller times. This option was employed to invert a possible time delay and compensate for topography under the assumption of a homogeneous velocity distribution (Sandmeier 2010, 220). Gain: This filter was applied with a start time of 6 ns, a linear gain setting of 0.8 * (1/pulsewith), a 0 exponent [db/m] setting and a maximum gain setting 10,000. This filter is designed to compensate for the rapid reduction in signal strength associated with the increase in depth of signal penetration. This filter also enables the display of data from all depths to be depicted simultaneously for each survey transect (Annan 2009, 34). Fix profile length: This allows a uniform number of traces to be created for each transect and allows for correction caused by the slight variation in numbers of traces caused by a variation in instrumentation or topography of the survey area (Sandmeier 2010, 246). Results and Interpretation Thirteen plots of the results from the seven survey areas are included in this report. These equate to vertical slices through the GPR data in the XY plane at approximately 12.5cm intervals. Further annotated plots of individual transects in the XZ plane are also included where it is felt they improve the understanding or the interpretation of features. A total of 140 transects were surveyed (Figure 3) and the full data set from each of these is available within the survey archive. The survey plots presented have been geo‐referenced to the Ordnance Survey National Grid. The inclusion of a further 13 plots, that overlay the results of excavations to the north and west of the church are also included and these are particularly useful for interpretation of features surveyed in [4]. Variation in material make‐up within the areas surveyed does mean that 5 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth although every effort has been made to reach an accurate calculation of depth there is still the potential for some inaccuracy. Further comparison with depths from known excavated remains would be a helpful future stage in refining the GPR data presented here. Area 1 An area 2 metres x 2 metres was surveyed with a series of N‐S, EW perpendicular traces with a traverse spacing of 0.3m and a sample interval of 0.05m. Internal fitments, including the pulpit and a grand piano, precluded extension of the survey area to the north or south. Features [1.1], [1.3], [1.4] and [1.7] appear to be the result of interference from electrical services and are seen as a disturbance to the GPR signal at all depths. Features [1.2], running east‐west and [1.6] running north‐south are probably make‐up for the floor. Feature [1.2] seems to be a continuation of [2.2] but is obscured at the western end by the interference from [1.3]. The northern edge of the southern support for the arcade between the nave and tower is represented by [1.5]. This feature equates to the northern edge of the southernmost pier base marked a in Figure 4 (Fernie 1983). Area 2 An area 2.7 metres x 2.5 metres was available for survey within the choir. Nine parallel transects, 0.3m apart, were measured using a sample interval of 0.05m. A series of linear features was detected between 0.17 metres and 0.5 metres these seem to represent a variation in material make‐up at this level. Two of the features [2.1] and [2.2] ran in an approximate east‐
west direction. A further feature [2.3] only appears at the 0.17 metre level. A curvilinear feature [2.5] was detected at the 1.02 metre level but it is unclear as to what this represents. It does, however, terminate at the location of feature [2.4] which seems to represent disturbance to the electro‐magnetic signal caused by a, presumably live, electrical conduit. This feature is also strongly present in area one where it continues in an east‐west direction. Area 3 The floor of the west tower was paved with stone flags and a number of storage cupboards had been inserted along its walls. Within this confined space an area measuring 3.0 metres x 2.6 metres was available for survey. Ten parallel transects, 0.3 metres apart, were measured using a sample interval of 0.05 metres. Features were detected between 0.15 metres and 1.68 metres after recalculation of the velocity to 0.075 m/ns. Analysis of the plots between 0.15 metres and 0.68 metres revealed a number of linear anomalies, [3.1],[3.4],[3.5] and [3.6] lying in an approximate north‐south direction. They are probably associated with the make‐up of the stone floor within the tower. Two further parallel features, [3.2] and [3.3], were only detected at the 0.15 metre level and were orientated in a northeast‐southwest direction. It is difficult to see their orientation could be associated with construction of the floor and their shallow nature would negate any suggestion of substantial structural remains. At a lower level an area of disturbance measuring 1.6 metres x 0.9 metres, [3.8], 3.9] and [3.11], was detected in the southwest corner of the survey area. Figure 5 presents an XZ profile of this area and shows that the response level within this area is highly variable. Although a number of linear features originally appeared to be present on the XY data plots, closer examination of individual traces suggest that these are visually misleading and that the area constitutes one larger structural anomaly. Area 4 An area measuring 50 metres x 12 metres at its widest point was surveyed in the churchyard north of the church. Fifty parallel transects, 1 metre apart, were measured using a sample 6 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth interval of 0.05 metres. A pathway, visible on the early editions of the Ordnance Survey [4.2] was detected at the northern edge of the survey and corroborates the data obtained from the resistance survey. The strongest response in the XY plots was produced at the 0.15 metre and 1.35 metre level which probably indicates the top and bottom of this feature. A number of potential graves were also detected [4.1] and produced widely varying responses. Some of the signatures from the survey, particularly those close to the excavated areas, produced similar responses in the XY plots but may be the result of the disturbance related to the excavation process. For the sake of clarity where any ambiguity remains such responses have been omitted from the interpretive plots. A northeast to southwest linear feature [4.3] was detected in the southeast corner of the survey area but was only present in the upper level. The most persistence response [4.4] was obtained in the previously excavated section of the porticus (Audouy M, 1984, 2). Although good results were obtained between 0.33 metres and 1.68 metres, previous excavations (ibid, 3) make it difficult to interpret these results. Data relating to the depth of excavated remains from Audouy’s report has proved particularly useful for corroborating the velocity calculations for the GPR (Audouy 1984,5). Only the northern edge of the excavation trench for the northern compartment of the narthex was included within the survey area. At the 1.35 metre level there were a number of strong responses [4.5] at the western edge of the survey area. Although these are the correct size and shape in XY plan for graves they were only detectable at the 1.35 metre level in the XZ sections. It is therefore unclear as to what these represent. Other features where it is difficult to produce a satisfactory interpretation include the parallel linear features [4.6] at the 1.5 metre level and [4.7] at the 1.84 metre level. The partial sub‐rectangular feature [4.8] at the 1.84 metre level is also equally problematic. Area 5 An area measuring 34 metres x 8 metres (at its widest) was surveyed in the churchyard west of the church. Eight parallel transects, 1m apart, were measured using a sample interval of 0.05 metres. A considerable slope was encountered in the north‐south direction but, given the lack of any real discoveries, this does not significantly affect the results. Reprocessing of the data from the surveys was carried out in an attempt to explain, amongst other questions, the absence of the ditch uncovered by Audouy in 1982 (Audouy 1984, 5). This should have been present at the northern edge of the survey but remains undetected in the GPR data. The reprocessing also clarified a number of linear east‐west anomalies that were originally thought to be features but now can probably be ascribed to changes in topography. Other than the modern path, the only discovery was a partial segment of a feature [5.3] possibly associated with the drain shown on Audouy’s plan at the point where it curves around the front of the tower. Area 6 An area measuring 17 metres x 12 metres was surveyed close to the southern boundary of the churchyard and east of the gate. Seventeen parallel transects, one metre apart, were measured using a sample interval of 0.05 metres. Feature [6.1] was a linear southwest‐northeast linear feature that was detected intermittently between 0.15 metres and 1.5 metres. The location of this feature coincides with a path or trackway shown on the early 1:2500 scale Ordnance Survey maps and although no longer visible above ground there appears to be sub‐surface survival. Feature 6.2 is an ephemeral linear northwest‐southeast anomaly that only occurs at the 0.34 metre level. It is, however, at an approximate right angle to [6.1] and may be associated. Similar in response is the linear northeast‐southwest feature [6.2] that only occurs at the 0.49 metre level. It is unclear what either of these discoveries represents. The final discovery was a 7 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth rectangular feature on the eastern edge of the survey area. This produced a response between 0.83 metres and 1.84 metres and may represent the edge of a grave. Area 7 Features were detected between depths of 0.17 metres and 1.35 metres. Figures 6 to 13 provide a series of XY slices of these features and Figure 5 presents two annotated XZ slices that show the characteristic inverted parabola indicative of structural remains. Analysis of the plots at greater depths, between 1.52 metres and the maximum penetration of 2.22 metres, failed to reveal evidence of further structural remains. An east‐west rectangular feature [7.6], to the north of the base of the altar steps, seems to indicate the presence of a substantial sub‐surface structural element. This is probably associated with the further substantial rectangular feature [7.3], along the same alignment and to the south of the altar steps, that produced a similar response to [7.6]. It was, however, only present at the eastern edge of the survey area. The changing shape and strength of response from both these features are possibly the reflections from differences in material make‐up used in the construction of this feature. Two east‐west, [7.5] and [7.6], weak linear features only occurring at the 1.35 metre level may be associated with the base of [7.1] and [7.3]. A further north‐south weak linear feature [7.4], perpendicular to [7.4] and [7.5] was also detected at this level but it is unclear as to what this represents. Resistivity Survey – Results and Interpretation The interpretation of the resistivity results (Figure 11) was carried out from a single plot of the results (Figure 10) without access to the original survey data. The original plot was manipulated using Surfer 9.0 and transferred to ArcGIS 9.3.1 where an interpolated surface was derived from the data. The object of this exercise was to provide a smoother, more refined, plot rather than attempt to enhance the data in any way. Without further access to the original data the interpretation of the results is by necessity conservative to avoid presentation of potentially misleading results. Features [5] and [7] at the eastern end of the churchyard are two rectilinear higher resistance anomalies that are possible structural remains. However, the large number of extant grave markers within this area of the churchyard may present an alternative explanation for this type of response from the survey. Feature [4] in the northwest corner of the survey denotes the edge of a rectangular band of high resistance but it is impossible to discern any individual elements within it. Features [2] and [3] are patches of high resistance that are probably associated with the pathways shown on the early Ordnance Survey 1:2500 editions (Figure 10). Feature [3] directly overlies the junction of two paths which would explain the size and shape of the response. Feature [1] is a linear band of variable higher resistance at the eastern end of the survey area. This represents another path or trackway shown on the early Ordnance Survey maps. Feature [6] is a partial rectangular anomaly that may represent the remains of a grave marker. The blank/dummy readings, visible on the plot to the north of the church, also follow the line of an earlier path or trackway. This feature appears on the GPR as [4.2]. 8 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 1 ‐ Location of the GPR surveys 9 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 2 ‐ Location of resistivity survey showing overlap with GPR surveys 10 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 3 ‐ Location of GPR survey traverses
11 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 4 ‐ Ground plan illustrating position of pier base in the chancel Figure 5 ‐ Area 2 interference from electrical services 12 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 6 ‐ Area 3 Transect 5 (velocity 0.075 m/ns) 13 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 7 ‐ Ordnance Survey (1:2500) 1st Revision, 1900 overlaying the GPR plots 14 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figu
re 8 ‐ Area 6 Transect 1 ‐ showing feature [6.4] 15 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 9 ‐ Area 7, transects 2 and 12, XZ trace profiles 16 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 10 ‐ Results of the resistivity survey 17 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 11 ‐ Interpretation of resistivity survey 18 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 12‐ Ordnance Survey (1:2500) 1st revision 1900 overlaying the resistivity plot 19 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Plots of Results ‐ Areas 1‐7 4.59ns‐ 49.46ns 20 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 13 ‐ Plot of GPR results 4.59ns (velocity 0.075m/ns) depth ~ 0.17m Figure 14 ‐ Plot of GPR results 9.09ns (velocity 0.075m/ns) depth ~ 0.34m 21 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 15 ‐ Plot of GPR results 13.47ns (velocity 0.075m/ns) depth ~ 0.50m 22 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 16 ‐ Plot of GPR results 18.06ns (velocity 0.075m/ns) depth ~ 0.68m 23 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 17 ‐ Plot of GPR results 22.51ns (velocity 0.075m/ns) depth ~ 0.84m 24 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 18 ‐ Plot of GPR results 27.09ns (velocity 0.075m/ns) depth ~ 1.02m 25 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 19 ‐ Plot of GPR results 31.54ns (velocity 0.075m/ns) depth ~ 1.18m 26 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 20 ‐ Plot of GPR results 36.12ns (velocity 0.075m/ns) depth ~ 1.35m 27 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 21 ‐ Plot of GPR results 40.57ns (velocity 0.075m/ns) depth ~ 1.52m 28 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 22 ‐ Plot of GPR results 45.01ns (velocity 0.075m/ns) depth ~ 1.68m 29 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 23 ‐ Plot of GPR results 49.46ns (velocity 0.075m/ns) depth ~ 1.85m 30 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Plot of GPR Results (4.59ns – 49.46ns) with excavation plans overlaid Figure 24 ‐ Excavation plans and GPR results 4.59ns (velocity 0.075m/ns) depth ~ 0.17m
31 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 25 ‐ Excavation plans and GPR results 9.09ns (velocity 0.075m/ns) depth ~ 0.34m 32 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 26 ‐ Excavation plans and GPR 13.47ns (velocity 0.075m/ns) depth ~ 0.50m 33 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 27 ‐ Excavation plans and GPR results 18.06ns (velocity 0.075m/ns) depth ~ 0.68m 34 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 28 ‐ Excavation plans and GPR results 22.51ns (velocity 0.075m/ns) depth ~ 0.84m 35 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 29 ‐ Excavation plans and GPR results 27.09ns (velocity 0.075m/ns) depth ~ 1.02m 36 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 30 ‐ Excavation plans and GPR results 31.54ns (velocity 0.075m/ns) depth ~ 1.18m 37 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 31 ‐ Excavation plans and GPR results 36.12ns (velocity 0.075m/ns) depth ~ 1.35m 38 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 32 ‐ Excavation plans and GPR results 40.57ns (velocity 0.075m/ns) depth ~ 1.52m 39 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 33 ‐ Excavation plans and GPR results 45.01ns (velocity 0.075m/ns) depth ~ 1.68m 40 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 34 ‐ Excavation plans and GPR results 49.46ns (velocity 0.075m/ns) depth ~ 1.85m 41 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Interpretation of the GPR plots – 4.59ns – 49.46ns Figure 35 ‐ Interpretation of GPR ‐ 4.59 ns ~ 0.15 metres 42 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 36 ‐ Interpretation of GPR ‐ 9.09 ns ~ 0.34 metres 43 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 37 ‐ Interpretation of GPR ‐ 13.47 ns ~ 0.50 metres 44 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 38 ‐ Interpretation of GPR ‐ 18.06 ns ~ 0.68 metres 45 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 39 ‐ Interpretation of GPR ‐ 22.51 ns ~ 0.84 metres 46 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 40 ‐ Interpretation of GPR ‐ 27.09 ns ~ 1.02 metres 47 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 41 ‐ Interpretation of GPR ‐ 31.54 ns ~ 1.18 metres 48 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 42 ‐ Interpretation of GPR ‐ 36.12 ns ~ 1.35 metres 49 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 43 ‐ Interpretation of GPR ‐ 40.57 ns ~ 1.52 metres 50 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 44 ‐ Interpretation of GPR ‐ 45.01 ns ~ 1.68 metres 51 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth Figure 45 ‐ Interpretation of GPR ‐ 49.46 ns ~ 1.85 metres 52 Ground Penetrating Radar Survey: All Saint’s Church, Brixworth References Annan, A.P. (2009) ‘Ground Penetrating Radar (GPR) Principles’ in Jol H.M. (ed.) Ground Penetrating Radar: Theory and Applications Audouy M (1984) ‘Excavations at the Church Of All Saintsʹ, Brixworth, Northamptonshire 1981‐
2’ in Journal of the British Archaeological Association, 137 Fernie, E. (1983) The Architecture of the Anglo‐Saxons Linford, N. (2006) ‘The application of geophysical methods to archaeological prospection’ in Reports on Progress in Physics, 69 pp.2205–2257 Sandmeier K.J. (2010) ReflexW 5.5 53