The effects of seasonal variation on archaeological detection using earth resistance: Preliminary...

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

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

• 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

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


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


Harnhill, Cirencester



Fluxgate gradiometer greyscale Quarry Field Heavy clay geology



Fluxgate gradiometer greyscale Quarry Field Heavy clay geology



Fluxgate gradiometer greyscale Cherry Copse Weathered limestone bedrock



Fluxgate gradiometer greyscale Cherry Copse Weathered limestone bedrock


Ground-truthing Quarry Field, Cirencester - Heavy Clay

Cherry Copse, Cirencester - Weathered Limestone

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


• 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

Monthly Surveys - FlashRes64


Ditch


ERT (FlashRes64 transects)






Earth Resistance (Multiplexed area survey)







Monthly Surveys – Twin Probe


Excavation trench

Kite photography courtesy of David Stott – Leeds University

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


Initial analysis - Earth Resistance

-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

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"


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


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


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"


Summer

Autumn

Winter

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


Autumn: -Resistivity decreased to a depth of 1m to June - Earth below 1m in depth remained the same resistivity as in the summer months


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

Well………

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

Well………


Well………


• 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)

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 (?)


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

Thank you for listening


The DART Project website: www.dartproject.info

Robert Fry [email protected]

http://www.dartproject.info/

Date post:	25-Dec-2014
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The effects of seasonal variation on archaeological detection using earth resistance: Preliminary...

Education