A presentation by Rob Fry at the 2012 Computer Applications in Archaeology conference in Southampton

1. 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

2. 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

3. The DART Project
Introduction
• Detection of Archaeological remains using Remote
sensing 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

4. 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

5. 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

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

7. Harnhill, Cirencester Introduction
Fluxgate gradiometer greyscale DART Project
Quarry Field
Heavy clay geology Seasonality
Fieldwork
Initial Data
Proposed
work

8. Harnhill, Cirencester Introduction
Fluxgate gradiometer greyscale DART Project
Quarry Field
Heavy clay geology Seasonality
Fieldwork
Initial Data
Proposed
work

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

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

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

12. 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 volumes
and in theory, depths of soil

13. Fieldwork
Monthly 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

14. Monthly Surveys - FlashRes64
Introduction
DART Project
Seasonality
Fieldwork
Initial Data
Proposed
work
Ditch

15. Introduction
ERT DART Project
(FlashRes64 transects)
Seasonality
Fieldwork
Initial Data
Proposed
work

16. Introduction
ERT DART Project
(FlashRes64 transects)
Seasonality
Fieldwork
Initial Data
Proposed
work

17. Introduction
ERT DART Project
(FlashRes64 transects)
Seasonality
Fieldwork
Initial Data
Proposed
work

18. Introduction
Earth Resistance FlashRes64
(Multiplexed area survey)
DART Project
Seasonality
Fieldwork
Initial Data
Proposed
work

19. Introduction
Earth Resistance FlashRes64
(Multiplexed area survey)
DART Project
Seasonality
Fieldwork
Initial Data
Proposed
work

20. Introduction
Earth Resistance DART Project
(Multiplexed area survey)
Seasonality
Fieldwork
Initial Data
Proposed
work

21. Introduction
Earth Resistance DART Project
(Multiplexed area survey)
Seasonality
Fieldwork
Initial Data
Proposed
work

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

23. 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
Fieldwork
Ohms
November 0.25m Ave
110 December 0.25m Ave
January 0.25m Ave Initial Data
Feburary 0.25m Ave
90
Proposed
70 work
50

24. 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
Ohms
-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

25. 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 seasons
Ohms
-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

26. 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 Ave
Ohms
60
November 0.25 Ave
December 0.25 Ave Initial Data
Janurary 0.25 Ave
50
Feburary 0.25 Ave
Proposed
40 work
30

27. 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 Seasonality
Ohms
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

28. 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
12
Ohms
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

29. Summer

30. Autumn

31. Winter

32. Change in resistivity through the
profile from June 2011

33. 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

34. 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

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

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

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

38. 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
9.10.11
16.10.11
23.10.11
winter, right?
30.10.11
6.11.11
13.11.11
20.11.11
27.11.11
4.12.11
11.12.11
• 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)

39. 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 (?)

40. Proposed Work
Introduction
Lots 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

41. Introduction
Thank you for listening
FlashRes64
DART Project
Seasonality
Fieldwork
The DART Project website:
www.dartproject.info
Initial Data
Proposed
work
Robert Fry
r.j.fry@student.bradford.ac.uk