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The effects of seasonal variation on archaeological detection using earth resistance: Preliminary results
from an ongoing study
Robert Fry
Chris Gaffney, Anthony Beck, David Stott
2012
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Introduction
• A study to aid archaeological detection
• Resistivity / Electromagnetics / Radar / TDR / Remote Sensing
• Prediction / Reliability / Detection / Interpretation
• Why?
•Known unknowns:
‘The problem with resistance data is that the ‘normal’
response can vary with the season’
Gaffney and Gater 2003:27
• Why now? •The DART Project
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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• Detection of Archaeological remains using Remote
sensing Techniques • The multi-temporal problems associated with heritage detection are
not just a domain of electrical resistance surveys
• Hyper-spectral imagery
• EM surveys
• Aerial photographic evidence
• In association with the Universities of Leeds, Birmingham,
Winchester and Nottingham
• Civil engineering, computing, geophysics, remote sensing, soil
engineering, data analysis and interpretation, knowledge engineering
• A multi-disciplinary framework to solve a multi-faceted problem
The DART Project Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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The DART Project Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
• The Universities of Leeds and Nottingham
• Hyper-spectral and spectral detection problems • Land use, Crop type/vigour/stress, Soil geology, Weather
• The University of Bradford
• Detection Problems associated with Electrical Resistance • Soil geology, Weather, Soil composition
• The University of Birmingham
• Soil Permittivity, Conductivity, and weather data analysis and comparison with GPR survey
• Soil engineering properties, Soil geology, Weather
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Test Areas
• 4 Test Areas • All ditches (old field boundaries or archaeological)
• 2 Situated on Clay soils
• 2 Situated on ‘Free draining’ soils
• 2 Locations • Harnhill, Cirencester • Diddington, Cambridgeshire
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Harnhill, Cirencester
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Harnhill, Cirencester
Fluxgate gradiometer greyscale Quarry Field Heavy clay geology
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Harnhill, Cirencester
Fluxgate gradiometer greyscale Quarry Field Heavy clay geology
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Harnhill, Cirencester
Fluxgate gradiometer greyscale Cherry Copse Weathered limestone bedrock
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Harnhill, Cirencester
Fluxgate gradiometer greyscale Cherry Copse Weathered limestone bedrock
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Ground-truthing Quarry Field, Cirencester - Heavy Clay
Cherry Copse, Cirencester - Weathered Limestone
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Fieldwork
Monthly Surveys – Twin Probe
Introduction FlashRes64 DART Project Seasonality Fieldwork Initial Data Proposed work
• 10m survey grid •0.5 x 0.5m resolution •4 multiplexed probe separations which can be equated with different volumes and in theory, depths of soil
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
• New technology – usually
a geological/hydrological
investigation.
• C.15,000 measurements
in 16 minutes
• Collects resistivity data in
section through the ground
Fieldwork
Monthly Surveys – FlashRes64 ERI
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Monthly Surveys - FlashRes64
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Ditch
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
ERT (FlashRes64 transects)
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
ERT (FlashRes64 transects)
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
ERT (FlashRes64 transects)
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Introduction FlashRes64 DART Project Seasonality Fieldwork Initial Data Proposed work
Earth Resistance (Multiplexed area survey)
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Introduction FlashRes64 DART Project Seasonality Fieldwork Initial Data Proposed work
Earth Resistance (Multiplexed area survey)
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Earth Resistance (Multiplexed area survey)
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Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Earth Resistance (Multiplexed area survey)
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Monthly Surveys – Twin Probe
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Excavation trench
Kite photography courtesy of David Stott – Leeds University
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Characteristic Seasonal Responses? Free Draining
50
70
90
110
130
150
170
190
Oh
ms
Cherry Copse (free-draining) Seasonal Relationship (a = 0.25m)
June 0.25m Ave
July 0.25m Ave
September 0.25m Ave
October 0.25m Ave
November 0.25m Ave
December 0.25m Ave
January 0.25m Ave
Feburary 0.25m Ave
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Initial analysis - Earth Resistance
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-30
-25
-20
-15
-10
-5
0
5
10
15
20
Oh
ms
Magnitude of anomaly at Cherry Copse (a=0.25m) after median filtering
June Median July Median September Median October Median
November Median December Median January Median Feburary Median
Characteristic Seasonal Responses? – Free Draining
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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-30
-25
-20
-15
-10
-5
0
5
10
15
20
Oh
ms
Magnitude of anomaly at Cherry Copse (a=0.25m) after median filtering
June Median July Median September Median October Median
November Median December Median January Median Feburary Median
Characteristic Seasonal Responses? – Free Draining
-30
-25
-20
-15
-10
-5
0
5
10
15
20
Oh
ms
Characteristic response over seasons
"Summer"
"Autumn"
"Winter"
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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Characteristic Seasonal Responses? – clay-on-clay
30
40
50
60
70
80
90
Oh
ms
Quarry Field (clay) Seasonal Relationship (a = 0.25m)
June 0.25 Ave
July 0.25 Ave
September 0.25 Ave
October 0.25 Ave
November 0.25 Ave
December 0.25 Ave
Janurary 0.25 Ave
Feburary 0.25 Ave
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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Characteristic Seasoanl Responses? – clay-on-clay
-8
-6
-4
-2
0
2
4
6
8
10
12
Oh
ms
Magnitude of anomaly at Quarry Field (a=0.25m) after median filtering
June Median July Median October Median September Median
November Median December Median Janurary Median Feburary Median
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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Characteristic Seasoanl Responses? – clay-on-clay
-8
-6
-4
-2
0
2
4
6
8
10
12
Oh
ms
Magnitude of anomaly at Quarry Field (a=0.25m) after median filtering
June Median July Median October Median September Median
November Median December Median Janurary Median Feburary Median
-8
-6
-4
-2
0
2
4
6
8
10
12
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
Characteristic response over seasons
Q"Summer"
Q"Autumn"
Q"Winter"
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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Summer
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Autumn
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Winter
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Change in resistivity through the profile from June 2011
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Change in resistivity through the profile from June 2011
Summer: -Generally increased resistivity (around 10-20% higher than June) -Between June and July the area around the feature decreased in resistivity
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Change in resistivity through the profile from June 2011
Autumn: -Resistivity decreased to a depth of 1m to June - Earth below 1m in depth remained the same resistivity as in the summer months
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Change in resistivity through the profile from June 2011
Autumn: -Resistivity decreased to a depth of 1m to June - Earth below 1m in depth remained the same resistivity as in the summer months
Winter: -Further decreasing in resistivity at surface (over 75% lower than in June) - Decrease resistivity at depths over 1 metre for the first time
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Well………
So it must have been a really wet winter, right?
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Well………
So it must have been a really wet winter, right?
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Well………
So it must have been a really wet winter, right?
• Large decrease in resistivity from summer into winter… • Moisture change? • Temperature change?
0
5
10
15
20
25
30
1.5
.11
8.5
.11
15
.5.1
1
22
.5.1
1
29
.5.1
1
5.6
.11
12
.6.1
1
19
.6.1
1
26
.6.1
1
3.7
.11
10
.7.1
1
17
.7.1
1
24
.7.1
1
31
.7.1
1
7.8
.11
14
.8.1
1
21
.8.1
1
28
.8.1
1
4.9
.11
11
.9.1
1
18
.9.1
1
25
.9.1
1
2.1
0.1
1
9.1
0.1
1
16
.10
.11
23
.10
.11
30
.10
.11
6.1
1.1
1
13
.11
.11
20
.11
.11
27
.11
.11
4.1
2.1
1
11
.12
.11
18
.12
.11
Rainfall (mm)
Survey
Temp max (⁰C)
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Thoughts so far…
• Resistivity decreases from summer to winter
• Seasonal data variation does exist – there are step changes between different seasons
• The measured response is greatest in the summer
• The decrease in resistivity at c.0.5-1m depths a function of temperature (not rainfall) in autumn
• The continuing decrease in resistivity at greater depths over winter due to both temperature and rainfall (?)
Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
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Proposed Work Introduction DART Project Seasonality Fieldwork Initial Data Proposed work
Lots more to do…
-Continuing monthly surveys until autumn 2012
- The influence of weather on the detection capabilities of the systems - Weather stations - in situ TDR and Temperature probes
- How does the resistivity response link to the aerial response in detection? Is there a link?
- Further studies planed for diurnal variations and induced weather events
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Thank you for listening
Introduction FlashRes64 DART Project Seasonality Fieldwork Initial Data Proposed work
The DART Project website: www.dartproject.info
Robert Fry [email protected]