This document summarizes a workshop on using electromagnetic radiation to detect archaeological sites. It discusses how different soil properties like water content, organic matter, and temperature can affect the permittivity and conductivity measured by ground penetrating radar and other electromagnetic techniques. Case studies from two fields in Diddington show how these measurements vary over time with rainfall, infiltration, and temperature. The document also compares measurements from IMKO probes to a Campbell Scientific TDR100, finding the probes less accurate but easier to install long-term. The overall aim is to better understand how soil characteristics influence electromagnetic readings and how these techniques can be used for long-term monitoring of archaeological sites.

1. School of Civil Engineering
Faculty of Engineering
Soils and Electromagnetic Radiation
DART Workshop
17th September 2013
Dan Boddice

2. • DART is focused on improving the detection of
archaeological sites through both aerial remote
sensing and geophysical techniques
• Many of these use EM radiation
• Ground penetrating radar (GPR)
• Airborne multi and hyper-spectral sensors
• Low frequency EM slingrams (e.g. EM38)
• Have different operating frequencies
Soils and EM Radiation
Why EM Radiation?

3. • Reflection of applied signal (Ar) is proportional to incident
signal (Ai) and a reflection coefficient defined using the EM
impedance
• Impedance is dependent on magnetic permeability (μ),
dielectric permittivity (ε) and electrical conductivity (σ) and
can defined
• We can take μ as reasonably constant but the other two
vary seasonally and with soil conditions
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Soils and EM Radiation
EM reflections

4. • EM technique used in soil science research
• Broadband EM pulse is sent through coaxial cable to the
probe
• Relative voltage is measured and plotted as function of time
allowing reflections due to changes in impedance to be
identified
• Measures hourly readings of
• Apparent Relative Dielectric Permittivity from travel time (linked to
water content via different models)
• Bulk Electrical Conductivity from signal loss after multiple reflections
Soils and EM Radiation
Time Domain Reflectometry
Robinson et al. 2005

5. Soils and EM Radiation
What affects the Permittivity and Conductivity?
• Water Content
• Variation is based on rainfall but water behaviour is affected by
soil properties and interactions with soil particles
• Particle surface area
• Density
• Porosity
• Organic Matter
• Chemistry
• Contrasts in soil water content are affected by differences in
• Storage – show as long term differences in values
• Infiltration – show as time variance between rain and
TDR readings

6. Soils and EM Radiation
What affects the Permittivity and Conductivity?
• Frequency of Signal
• Depends on instrument used
• Causes variations in measured values
• Soil Temperature
• Variation is Seasonal and Diurnal
• Temperature affects water behaviour-bound
water, viscosity, ion mobility etc.
• The effect on geophysical properties and the extent of its
importance is debated

7. Soils and EM Radiation
Diddington Clay Field

8. Soils and EM Radiation
Diddington Clay Field: Permittivity

9. Soils and EM Radiation
Diddington Clay Field: Conductivity

10. Soils and EM Radiation
Diddington Clay Field: Importance of Temperature

11. Soils and EM Radiation
Diddington Clay Field: Temperature

12. Soils and EM Radiation
Diddington Pasture Field

13. Soils and EM Radiation
Diddington Pasture Field: Permittivity

14. Soils and EM Radiation
Diddington Pasture Field: Conductivity

15. Soils and EM Radiation
Diddington Pasture Field: Importance of Temperature

16. Soils and EM Radiation
Diddington Pasture Field: Temperature

17. Youngs and Poulovassilis 1976
Soils and EM Radiation
The Different Forms of Moisture Profile Development During the
Redistribution of Soil Water After Infiltration
Fine Grained and Deep Coarse Grained and Shallow

18. Soils and EM Radiation
Diddington Clay Field: Infiltration

19. Soils and EM Radiation
Diddington Clay Field: Infiltration

20. Soils and EM Radiation
IMKO Probes Vs Campbell Scientific TDR100: VWC/Apparent Permittivity
Thanks to Van Walt Ltd. for the equipment loan

21. Soils and EM Radiation
IMKO Probes VS Campbell Scientific TDR100: BEC
Soils and EM Radiation
IMKO Probes Vs Campbell Scientific TDR100: BEC
Thanks to Van Walt Ltd. for the equipment loan

22. ADVANTAGES
• Faster and easier to install
• Minimal soil disturbance
• Capable of identifying trends in VWC and BEC
• Telemetry gives a data stream minimising site visits
• Simpler interface and no need to process data
DISADVANTAGES
• Undefined measurement volume
• Plastic tube and electrode coating makes BEC determination
problematic
• Model may not fit all soils and hard even with conversion to
permittivity to fit other models because of tube effects make
changes smaller-Needs empirical calibration to overcome
this rather than existing models
What is the overall aim of the experiment?
Soils and EM Radiation
IMKO Probes VS Campbell Scientific TDR100
Thanks to Van Walt Ltd. for the equipment loan

23. • Greatest difference seems to be in water held in the bottom ditch fill for both
sites for both apparent permittivity and BEC-field capacity is higher
• Magnitude of difference is greater in coarser grained soils
• Infiltration tends not to affect below the top 30 - 40 cm except in cases of
extreme drying beforehand
• Temperature has very minor role on permittivity but quite a large role on BEC
especially at saturation
• How to monitor soil properties long term
• Flooding
• Animal damage
• Settling-should we wet the probes in?
• Work is Still Ongoing
• Two more sites at RAC, Cirencester
• Need to link behaviour to soil properties
Soils and EM Radiation
What have we learnt: Some Thoughts from Ongoing Work?

24. Soils and EM Radiation
Acknowledgments
• EQUIPMENT LOANS
• Van Walt Ltd.
• Utsi Electronics Ltd.
• OTHER SUPPORT
• Giulio Curioni and Andrew Foo (Mapping the Underworld)
• Nicole Metje and David Chapman (Birmingham University)