This document discusses using Time Domain Reflectometry (TDR) to monitor the geophysical properties of archaeological residues over time. TDR devices were installed at archaeological sites to take hourly readings of soil permittivity, conductivity, and temperature both within and outside of archaeological features. The data collected can help understand contrasts in electromagnetic properties between residues and surrounding soils. Challenges during the monitoring process and examples of preliminary permittivity, conductivity, and temperature data are presented. Future work is proposed to further analyze the relationship between geophysical properties, soil characteristics, and weather conditions.

1. Using Time Domain Reflectometry (TDR) to
Monitor the Geophysical Properties of
Archaeological Residues
Dan Boddice, Laura Pring, Dr. Nicole Metje, Dr. David Chapman
School of Civil Engineering
College of Engineering and Physical Sciences

2. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
The Problem
• DART is focused on improving the detection of archaeological sites
through both aerial remote sensing and geophysical techniques
• Many of these use Electromagnetic (EM) radiation and require a
contrast in EM properties
• Ground penetrating radar (GPR)
• Airborne multi and hyper-spectral sensors
• Low frequency EM slingrams (e.g. EM38)
• Other techniques use electrical properties
• Electrical resistance surveying
1. EVIDENCE FOR SOIL CONTRASTS IS ANECDOTAL
2. POOR DETECTION RATES ON CERTAIN SOILS

3. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
The Problem
KEY QUESTION: Can prior knowledge of geotechnical and
climatic factors improve our understanding of the
geophysical contrast factors between archaeological
residues and the surrounding soil matrix
• To map the soil and archaeological residues geophysical properties
and identify the contrasts between them through a long term
monitoring strategy.
• Find ways to use the geotechnical properties of the soil, and weather
data to predict sensor response and inform sensor choice.
• Develop an appropriate methodology for similar or follow-on projects
studying other geologies and archaeological feature types

4. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
EM radiation and Permittivity Basics
• EM transmission is governed by complex permittivity which
varies according to changing ground conditions
• Real permittivity is the ability to store and release energy
through charge separation
• Can occur due to separation of charges in atom, movement of ions or
rotation of molecules in line with applied field
• Governs the speed of EM radiation propagation as produces
displacement electrical field
• Difference in layers will determine size of reflection
• Imaginary Permittivity causes loss of signal energy
• Relaxation mechanisms – lag in polarisation with applied field
• Conductivity - causes the energy to attenuate as a function of distance

5. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Permittivity
SOIL TYPE DIELECTRIC PERMITTIVITY
Air 1
Water 80-81
Dry Sand 3-5
Dry Silt 3-30
Asphalt 3-5
Limestone 4-8
Granite 4-6
Shale 5-15
Clay 5-40
Organic rich surface soil 12
Saturated sand 20-30
Adapted from Conyers 2004

6. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
TDR Operating Principals

7. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Design and Installation
Requirements
• Needs to take hourly readings of permittivity, conductivity
and temperature
• Needs probes both in and out of archaeological feature and
at different depths
• Needs constant power supply
• Needs some kind of communication

8. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Design and Installation

9. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Design and Installation: clay sites

10. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Design and Installation: simpler sites

11. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Design and Installation

12. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Waveform Interpretation
• Identifying start and end reflection points takes time
• 16 permittivity per hour
• c.11520 per station per month
• Currently 6 stations –too many to do this manually!
• Conductivity data is simpler
• Quantity is the same as for permittivity
SOLUTION: Script needed

13. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Other Challenges Since Installation
• Loggers behaving erratically
• Skipped readings and scans
• Unexplained stopping
• Solved by slowing the scan rate and switching CF card brand
• Animal Damage
• Weather Station cables eaten
http://free-extras.com/images/elmer_fudd-5189.htm
• Probes re-excavated
• Telemetry system will reduce future loss of data

14. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Example data: Permittivity

15. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Example data: Conductivity

16. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
Example data: Temperature

17. Using TDR to Monitor the Geophysical Properties of Archaeological
Residues
The future?
• Complete geotechnical analysis on soils from the lab to
categorise them
• Create a link between permittivity, moisture content and
bulk density using the TDR on prepared samples in the lab
• Analyse frequency dependence of soils in different states in
the lab
• Continue to analyse data flow using statistical tests and
time delay correlation

18. Progress Update
Acknowledgments
The Rest of the DART Project
• Dave Stott , Dr. Anthony Beck and Dr. Anthony Cohn (University of
Leeds)
• Rob Fry and Dr. Chris Gaffney (University of Bradford)
• Dr. Keith Wilkinson (University of Winchester)
• The other stakeholders and academic consultants
Also
• Giulio Curioni and Andrew Foo (Mapping the Underworld)