The effects of seasonal variation on archaeological detection using earth resistance: Preliminary results from an ongoing study

The effects of seasonal variation on archaeologicaldetection using earth resistance: Preliminary results from an ongoing study Robert Fry Chris Gaffney, Anthony Beck, David Stott 2012

Introduction Introduction• A study to aid archaeological detection • Resistivity / Electromagnetics / Radar / TDR / Remote Sensing DART Project • Prediction / Reliability / Detection / Interpretation Seasonality• Why? •Known unknowns: Fieldwork ‘The problem with resistance data is that the ‘normal’ response can vary with the season’ Initial Data Gaffney and Gater 2003:27 Proposed work• Why now? •The DART Project

The DART Project Introduction• Detection of Archaeological remains using Remotesensing Techniques DART Project • The multi-temporal problems associated with heritage detection are not just a domain of electrical resistance surveys • Hyper-spectral imagery Seasonality • EM surveys • Aerial photographic evidence Fieldwork • In association with the Universities of Leeds, Birmingham, Initial Data Winchester and Nottingham • Civil engineering, computing, geophysics, remote sensing, soil engineering, data analysis and interpretation, knowledge engineering Proposed work • A multi-disciplinary framework to solve a multi-faceted problem

The DART Project• The Universities of Leeds and Nottingham Introduction • Hyper-spectral and spectral detection problems • Land use, Crop type/vigour/stress, Soil geology, Weather DART Project Seasonality• The University of Bradford • Detection Problems associated with Electrical Resistance Fieldwork • Soil geology, Weather, Soil composition Initial Data Proposed work• The University of Birmingham • Soil Permittivity, Conductivity, and weather data analysis and comparison with GPR survey • Soil engineering properties, Soil geology, Weather

Test Areas• 4 Test Areas Introduction • All ditches (old field boundaries or archaeological) DART Project• 2 Situated on Clay soils Seasonality• 2 Situated on ‘Free draining’ soils Fieldwork Initial Data• 2 Locations • Harnhill, Cirencester Proposed work • Diddington, Cambridgeshire

Harnhill, Cirencester Introduction DART Project Seasonality Fieldwork Initial Data Proposed work

Harnhill, Cirencester IntroductionFluxgate gradiometer greyscale DART ProjectQuarry FieldHeavy clay geology Seasonality Fieldwork Initial Data Proposed work

Harnhill, Cirencester Introduction Fluxgate gradiometer greyscale DART Project Cherry Copse Weathered limestone bedrock Seasonality Fieldwork Initial Data Proposed work

Quarry Field, Cirencester - Heavy Clay Ground-truthing Introduction DART Project Seasonality FieldworkCherry Copse, Cirencester - Weathered Limestone Initial Data Proposed work

Fieldwork Monthly Surveys – Twin Probe Introduction FlashRes64 DART Project Seasonality Fieldwork Initial Data• 10m survey grid Proposed•0.5 x 0.5m resolution work•4 multiplexed probe separations which can be equated with different volumesand in theory, depths of soil

FieldworkMonthly Surveys – FlashRes64 ERI • New technology – usually Introduction a geological/hydrological investigation. DART Project • C.15,000 measurements in 16 minutes Seasonality • Collects resistivity data in section through the ground Fieldwork Initial Data Proposed work

Monthly Surveys - FlashRes64 Introduction DART Project Seasonality Fieldwork Initial Data Proposed workDitch

IntroductionERT DART Project(FlashRes64 transects) Seasonality Fieldwork Initial Data Proposed work

IntroductionEarth Resistance FlashRes64(Multiplexed area survey) DART Project Seasonality Fieldwork Initial Data Proposed work

IntroductionEarth Resistance DART Project(Multiplexed area survey) Seasonality Fieldwork Initial Data Proposed work

Monthly Surveys – Twin Probe Introduction DART Project Seasonality Fieldwork Initial Data Proposed work Excavation trenchKite photography courtesy of David Stott – Leeds University

Initial analysis - Earth Resistance Characteristic Seasonal Responses? Free Draining Introduction Cherry Copse (free-draining) Seasonal Relationship (a = 0.25m) 190 DART Project 170 Seasonality June 0.25m Ave 150 July 0.25m Ave September 0.25m Ave 130 October 0.25m Ave FieldworkOhms November 0.25m Ave 110 December 0.25m Ave January 0.25m Ave Initial Data Feburary 0.25m Ave 90 Proposed 70 work 50

Characteristic Seasonal Responses? – Free Draining Magnitude of anomaly at Cherry Copse (a=0.25m) after median filtering Introduction 20 15 DART Project 10 5 Seasonality 0Ohms -5 Fieldwork -10 -15 Initial Data -20 -25 Proposed -30 work June Median July Median September Median October Median November Median December Median January Median Feburary Median

Characteristic Seasonal Responses? – Free Draining Magnitude of anomaly at Cherry Copse (a=0.25m) after median filtering Introduction 20 15 DART Project 10 5 Seasonality 0 Characteristic response over seasonsOhms -5 20 Fieldwork -10 15 -15 10 Initial Data -20 5 -25 0 "Summer" Proposed Ohms -30 -5 "Autumn" work June Median July Median September Median October Median "Winter" -10 November Median December Median January Median Feburary Median -15 -20 -25 -30

Characteristic Seasonal Responses? – clay-on-clay Introduction Quarry Field (clay) Seasonal Relationship (a = 0.25m) 90 DART Project 80 Seasonality June 0.25 Ave 70 July 0.25 Ave September 0.25 Ave Fieldwork October 0.25 AveOhms 60 November 0.25 Ave December 0.25 Ave Initial Data Janurary 0.25 Ave 50 Feburary 0.25 Ave Proposed 40 work 30

Characteristic Seasoanl Responses? – clay-on-clay 12 Introduction Magnitude of anomaly at Quarry Field (a=0.25m) after median filtering 10 8 DART Project 6 4 SeasonalityOhms 2 0 Fieldwork -2 -4 Initial Data -6 -8 Proposed work June Median July Median October Median September Median November Median December Median Janurary Median Feburary Median

Characteristic Seasoanl Responses? – clay-on-clay 12 Introduction Magnitude of anomaly at Quarry Field (a=0.25m) after median filtering 10 8 DART Project 6 Characteristic response over seasons 4 Seasonality 12Ohms 2 10 0 Fieldwork 8 -2 6 -4 Initial Data 4 Q"Summer" -6 2 Q"Autumn" -8 Q"Winter" Proposed 0 work 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 -2 June Median July Median October Median September Median -4 November Median December Median Janurary Median Feburary Median -6 -8

Summer

Autumn

Winter

Change in resistivity through the profile from June 2011

Change in resistivity through the profile from June 2011Summer:-Generally increased resistivity (around 10-20% higher than June)-Between June and July the area around the feature decreased in resistivity

Change in resistivity through the profile from June 2011Autumn:-Resistivity decreased to a depth of 1m toJune- Earth below 1m in depth remained thesame resistivity as in the summer months

Change in resistivity through the profile from June 2011Autumn:-Resistivity decreased to a depth of 1m toJuneWinter:- Earth below 1m in depth remained thesame resistivity as inin resistivity at surface-Further decreasing the summer months(over 75% lower than in June)- Decrease resistivity at depths over 1 metrefor the first time

So it must have been a really wet winter, right?Well………

10 15 20 25 30 0 5 1.5.11 8.5.11 15.5.11 22.5.11 29.5.11 5.6.11 Well……… 12.6.11 19.6.11 26.6.11 3.7.11 10.7.11 17.7.11 24.7.11 31.7.11 7.8.11 • Moisture change? 14.8.11 21.8.11 • Temperature change? 28.8.11 4.9.11 11.9.11 18.9.11 25.9.11 2.10.11 9.10.1116.10.1123.10.11 winter, right?30.10.11 6.11.1113.11.1120.11.1127.11.11 4.12.1111.12.11 • Large decrease in resistivity from summer into winter…18.12.11 So it must have been a really wet Survey Rainfall (mm) Temp max (⁰C)

Thoughts so far… Introduction• Resistivity decreases from summer to winter DART Project• Seasonal data variation does exist – there are step changes between different seasons Seasonality Fieldwork• The measured response is greatest in the summer Initial Data• The decrease in resistivity at c.0.5-1m depths a function of temperature (not rainfall) in autumn Proposed work• The continuing decrease in resistivity at greater depths over winter due to both temperature and rainfall (?)

Proposed Work IntroductionLots more to do… DART Project-Continuing monthly surveys until autumn 2012 Seasonality- The influence of weather on the detection capabilities of the systems - Weather stations - in situ TDR and Temperature probes Fieldwork- How does the resistivity response link to the aerial response in detection?Is there a link? Initial Data- Further studies planed for diurnal variations and induced weather events Proposed work

IntroductionThank you for listening FlashRes64 DART Project Seasonality FieldworkThe DART Project website: www.dartproject.info Initial Data Proposed work Robert Fry r.j.fry@student.bradford.ac.uk

The effects of seasonal variation on archaeological detection using earth resistance: Preliminary results from an ongoing study

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The effects of seasonal variation on archaeological detection using earth resistance: Preliminary results from an ongoing study Presentation Transcript