Geophysical Survey Report of Blickling Estate Norfolk
New Car Park
For National Trust
Magnitude Surveys Ref: M STG127 _2
HER Event Number: ENF142213
May 2017 Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report
Unit 17, Commerce Court
Challenge Way
Bradford
BD4 8NW
01274 926020
Report Written by:
Finnegan Pope - Carter BSc MSc FGS Figures Produced by:
Julia Cantanaro BSc MSc
Report Checked by: Dr. Chrys Harris BA MSc PhD
Repor t Issued: 16 May 2017
Abstract Magnitude Survey s was commissioned to assess a c. 0.47ha area of land Blickling Estate, Norfolk through geophysical survey. A ground penetrating radar survey was successfully completed and no anomalies of a probable or possible archaeologi cal origin have been identified. The survey is characterised by a marked difference in response between the eastern and western halves, which reflects differences in the site’s current land usage. In the western half of site, t he results are impacted by the road surfaces and usage as a car park. In contrast, the eastern half of site is quieter and reveals natural variations within the soil and geology.
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Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report Contents Abstract ...... 2 List of Figures ...... 4 1. Introduction ...... 5 2. Quality Assurance ...... 5 3. Objectives ...... 5 4. Geographic Ba ckground ...... 6 5. Archaeological Background ...... 6 6. Methodology ...... 8 Data Collection ...... 8 Dat a Processing ...... 8 Data Visualisation and Interpretation ...... 8 7. Results ...... 9 Qualification ...... 9 Discussion ...... 9 Interpret ation ...... 9 General Statements ...... 9 GPR Results – Specific Anomalies ...... 9 Indicative Radargrams ...... 10 8. Conclusions ...... 10 9. Archiving ...... 10 10. Copyright ...... 11 11. References ...... 11
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Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report L ist of Figures Figure 1: Site Location 1:25,000 @ A4
Figure 2: Location of Survey Area s 1: 2500 @ A3
Figure 3: Indicative GPR Timeslices 1: 1000 @ A3
Figure 4: Indicative GPR Timeslices and Interpretation 1: 1000 @ A3
Figure 5 : Combined Interpretations Over Historic Mapping 1: 1000 @ A3
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Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report
1. Introduction Magnitude Surve ys Ltd (MS) was commissioned by the National Trust to undertake a geophysical survey across a c. 0.47 ha area over a cark park (TG 17471 28648) at Blickling Estate, Norfolk.
T he geophysical survey comprised hand - pushed, cart - mounted ground penetrating radar (GPR) surv ey. MS’ Ofcom Ground Probing Radar licence number is L1078291/1.
The survey was conducted in line with the current best practice guidelines p roduced by Historic England (David et al ., 2008) , the Charte re d Institute for Archaeologists (CIfA, 2014) and the European Archaeological Council (Schmidt et al ., 2015).
The survey commenc ed on 11 April 2017 and took one day to complete.
2. Quality Assurance Project management, survey work , data processing and report production ha ve been carried out by qualified and pro fessional geophysicists to standards exceeding the current best practice (CIfA, 2014; David et al . , 2008, Schmidt et al ., 2015).
Magnitude Surveys is a corporate member of ISAP (International Society of Archaeological Prospection).
Director Graeme Attwood is a Member of the Chartered Institute for Archaeologists (CIfA), the chartered UK body for archaeologists, as well as the Secretary of GeoSIG, the CIfA Geophysics Special Interest Group. Director Finnegan Pope - Carter is a Fellow of the Lond on Geological Society, the chartered UK body for geophysicists and geologists, as well as a member of GeoSIG, the CIfA Geophysics Special Interest Group. Director Chrys Harris has a PhD in archaeological geophysics from the University of Bradford.
All MS m anagers have postgraduate qualifications in archaeological geophysics. All MS field staff have relevant archaeology or geophysics degrees and supervisors have at least three years ’ field experience.
3. O bjectives The geophysical survey aimed to assess the subsurface archaeological potential of the survey area.
Magnitude Surveys Ltd 5 | P a g e Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report 4. Geographic Background The site is located within Blickling Estate, Norfolk ( Figure 1), which lies c. 20km north of Norwich . Survey was undertaken c. 450m south - west of Blickling Hall, over an area u sed for parking cars (Figure 2).
The underlying geology comprises Wroxham Crag Formation — sand and gravel with superficial deposits of Brickearth — Clay, Silt and Sand over both areas ( British Geological Survey , 2017).
The soils are described as freely draining slightly acid loamy soils (Soilscapes, 2017).
Survey c onsiderations :
Survey Ground Conditions Further notes: Area 1 Flat area used for parking A tree was located towards the centre of the cars. Mixture of grass and survey are and in the north - western corner. A roll concrete in the western half, of plastic mesh was no ted in the ground towards with plastic mesh beneath the north - eastern corner. A paved road lead into grass in the eastern half. the site from the south, with alternating paved and grass areas to the west. Cars parked in the grassy areas. The area was bounded by bushes and trees on all sides.
5. Archaeological Background The following archaeological background summarises information compiled from an archaeological and historic landscape survey report by NAU Archaeology (Penn, 2017) and a search of the Norfolk Historic Environment Record.
The Blickling Estate en compasses Blickling Hall and an expansive site of gardens, woods and parkland. While the present Jacobean manor house of Blickling Hall is an early 17 th century construction, it was built on th e remains on an earlier moated m edieval and Tudor house. The vi llage of Blickling is recorded in the Domesday Book; although its exact location is unknown. Evidence for earlier archaeological activity has been ide ntified in the area, including prehistoric a ctivity and a number of cropmark features that have been inter preted as having a tentative Roman origin. Prehistoric activity is primarily evidence d by isolated finds within the e state. A large mound in Leaselands Woods is considered to represent a Bronze Age barrow. Aerial photograph analysis has interpreted a numbe r of cropmarks to possibly reflect the remnants of ploughed out barrows. A rectilinear enclosure with internal sub divisions has been identified in aerial photographs c. 640 m south - east of site (NHER 36072). These cropmarks have been interpreted with a ten tative Roman origin; however, they could also reflect features associated with the estate’s agricultural or parkland landscape. An isolated find of Roman pottery (NHER 31651) is recorded c. 75m north of this enclosure.
Historic mapping of the site records the survey area and its surrounding vicinity as comprisi ng enclosed fields. A range of post - medieval and m odern activity is known in the wider a rea, including a brickworks c. 675 m south - west of site (NHER 12550), pumping stations (NHER 13486, 29278), and q uarries. A map regression undertaken of available historic Ordnance
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Survey mapping tracks the evolution of site’s configuration . The survey area is recorded as a nursey in the 1 st Edition Ordnance Survey Norfolk County Series from 1885. A footpath is denot ed running on a rough north - south alignment through the area, which connects the area to the main road. The location and orientation of this footpath correlates with a modern paved road, which was present at the time of survey (see Section 4.4). A minor fo otpath is denoted running perpendicular, which effectively segments the nursey into quadrants. A boundary to the west of the main footpath demarcates the western limit of the nursery area. While the main footpath is recorded throughout until the 1971 Ordna nce Survey Plan, the minor footpath and western boundary are not recorded on the 2 nd Edition Ordnance Survey map from 1907. The surrounding areas are recorded as wooded as well. A Lodge is marked to the east of the survey area and is present throughout the 20 th century. During World War II, the RAF Oulton bomber base was established on the Blickling Estate and its outbuildings were used for military operations. Maps of the site record a number small, ephemeral structures to the west of the survey area, whic h were still recorded on the 1950 Ordnance Survey Provisional Edition. There was recorded tree clearance within the Estate during WW2 for “Dig for Victory,” but the vicinity is still recorded under trees.
Magnitude Surveys Ltd 7 | P a g e Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report 6. Methodology Data Collection Geophysical prospection comprised GPR as described in the following table.
Table of survey strategies:
Method Instrument Traverse Interval Sample Interval Ground Mala X3M with a Penetrating 0.5 m 0.05 m 450MHz antenna Radar
GPR data were collected along lines, using the system’s odometer wheel to position sampling points. The lines were set out within a grid established using a Hemisphere S321 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.
Data P rocessing GPR d ata were processed in the standard commercial software package ReflexW 3D. GPR Processing steps were limited to:
DC Shift – The waveform response for each traverse was centred to correct for striping e ffects caused by small v ariations in sen sor electronics and orientation.
Bandpass Filte r – Frequencies outside the normal range of the measuring antennae were filtered out to remove errors from external sources.
Gain Adjust – A gain curve was manually calculated to account for signal attenuation with depth. The gain adjust allows features at depth with a weaker signal to be resolved at the same plotting scale as near surface features.
Hyperbola fitting – Manual fitting of hyperbola curves was conducted to calculate the velocity of the wave. This allows the calculation of response depth from response time.
Data Visualisation and Interpretation The individual GPR radargrams have been stacked to form a three - dimensional cube of measurements. Greyscales have been created by horizontally slicing the cu be to produce plan - view timeslices . These “time slices ” were initially considered in an animated GIF form to analyse the three - dimensional extent of a nomalies. For print purposes, three gross soil volumes are considered: shallow, middle, and deep. The mean of the timeslices within each gross soil volume was taken and used as a representative time slice for the interpretation figures. Timeslices were interpreted in a layered environment, overlaid against open street mapping, satellite imagery, historic mappin g, LiDAR data, and soil and geology mapping. The timeslices were also interpreted in consideration with the radargrams, which visualise the form of the geophysical response, aiding in anomaly interpretation.
Magnitude Surveys Ltd 8 | P a g e Blickling Estate, Norfolk (New Cark Park) MSTG127_2 - Geophysical Survey Report 7. Results Qualification Geophysical results are not a map of the ground and are instead a direct measurement of subsurface properties. Detecting and mapping features requires that said features have properties that can be measured by the chosen technique(s) and that these properties have sufficient contrast with the background to be identifiable. The interpretation of any identified anomalies is inherently subjective. W hile the scrutiny of the results is undertaken by qualified, experienced individuals and rigorously checked for quality and consiste ncy , it is often not possible to classify all anomaly sources . Where possible an anomaly source will be identified along with the certainty of the interpretation. The only way to improve the interpretation of result s is through a process of comparing excav ated resul ts with the geophysical reports. MS actively seek feedback on their reports as well as reports of further work in order to constantly improve our knowledge and service. Discussion The GPR survey has produced variable results the survey environmen t. The western half of the area is impact ed by the effect of modern activity, with the current configuration of the roads and car parking spaces evi dent throughout the timeslices. In contrast, the eastern half of site is much quieter and the results over t his area primarily represent mino r n atural variati ons within the soils and geology . Several responses have been classified as “Undetermined,” but are considered more likely to represent a combination of modern and natural processes than reflect archaeologi cal activity .
Interpretation General Statements 7.3.1.1. G eophysical anomalies will be discussed broadly as classification types across the survey area. O nly anomalies that are distinctive or unusual will be discussed individually .
7.3.1.2. Undetermined – Anomalies are classified as U ndetermined when the anomaly origin is ambiguous through the geophysical results and there is no supporting or correlative evidence to warrant a more certain classification . These anomalies are likely to be the result of geological , ped ological or agricultural processes -- although an archaeological origin cannot be entirely ruled out . GPR Results – Specific Anomalies 7.3.2.1. Industrial/Modern (Spread) – Strong reflections are evident in the near surface which follow the alig nment of the current car park roads. To wards the south - west of the survey area , a strong broad response across the roads and parking bays is evident with characteristics similar to the roads’ response s. I t is likely th at this is the result of ground compaction caused by parked vehicles. Echoes of these roads and bay responses can be seen throughout the radargrams causing shadows to occur at deeper depths (see 7.3.3) . This is most likely an effect of t he refraction of the transmitted wave, due to a significant velocity change at the interfaces of the superficial material associated with the car park.
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7.3.2.2. Industrial/Modern – A strong discrete near surface reflector [ A ] is evident towards the north - east of the survey area. The location of this respon ses correlates with a compacted roll of plastic meshin g evident on the ground surface (see Section 4.4). Indicative Radargrams A
8. Conclusions A ground pen etrating radar survey has been successfully completed across the survey area. No anomalies of a probable or possible archaeological have been identified; however, the results are characterised by a distinct division between the eastern and western half of site. T he western half of the survey area has been impacted by the modern usa ge of the site as a car park . Strong reflections from the road surface and the parking bays have been detected across the western half of site. The net refraction of the transmitted signal may have limited the ability to detect more deeply buried features in this area . Deeper features may have been masked by shadows caused by these near surface features. The eastern half of site is much quieter in comparison, revealing minor natural variations within the soil and geology.
9. Archiving MS maintains an in - hous e digital archive , which is based on Schmidt and Ernenwein ( 2013 ) . This stores the collected measurements, unprocessed and processed data, georeferenced and un - georeferenced images , radargrams and a copy of the final report.
MS contributes all reports to the ADS Grey Literat ure Library subject to any time embargo dictated by the client.
Whenever possible , MS has a policy of making data available to view in easy to use forms on its website. This can benefit the client by making all of their reports availabl e in a single repository,
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while also being a useful resource for research. Should a client wish to impose a time embargo on the availability of data , this can be achieved in discussion with MS.
10. Copyright Copyright and the intellectual property pertaining to all reports, figures, and datasets produced by Magnitude Services Ltd. is retained by MS. The client is given full licence to use such material for their own purposes. Permission must be sought by any third party wishing to use or reproduce any IP owned by MS.
11. References British Geological Survey, 2017 . Geology of Britain. [ Blickling, Norfolk ]. [ http://mapapps.bgs.ac.uk/geologyofbr itain/home.html/ ]. [Accessed 24/04/2017 ]. Charted Institute for Archaeologists, 2014. Standards and g uidance for archaeological geophysical survey. CIfA . David, A., Linford, N., Linford, P. and Martin, L., 2008. Geophysical s urvey in a rchaeological f ield e valuation: r esearch and p rofessional s ervices g uidelines (2 nd edition). Historic England . Google Eart h, 2017. Google Earth Pro V 7.1.7.2606 . 52.811969, 1.228534 ©201 7 Google © Getmapping plc.
Penn, K., 2007. Blickling Estate, Norfolk: Archaeological and historic landscape survey. A report for the National Trust. Unpublished report by NAU Archaeology. Schm idt, A. and Ernenwein, E., 2013. Guide to Good Practice: Geophysical Data in Archaeology. 2nd e d ., Oxbow Books, Oxford. Schmidt, A., Linford, P., Linford, N., David, A., Gaffney, C., Sarris, A. and Fassbinder, J., 2015. Guidelines for the use of geophysics in archaeology: questions to ask and points to consider. EAC Guidelines 2. European Archaeological Council: Belgium.
S oilscapes, 2017 . [ Blickling, Norfolk ] . C ranfield University, Nat ional Soil Resources Institute [ http://landis.org.uk ]. [ Access ed 24/04/2017 ] .
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