Changing geophysical contrast between archaeological features and surrounding soil

Boddice, Daniel (2015). Changing geophysical contrast between archaeological features and surrounding soil. University of Birmingham. Ph.D.

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Abstract

Electromagnetic (EM) techniques are used to locate and map archaeological features through differences in soil EM properties (linked to geotechnical properties and climatic conditions), but these have poorly understood seasonality to their response, and poor performance on certain (especially fine grained) soils. Customised Time Domain Reflectometry (TDR) monitoring stations were used to collect hourly apparent relative dielectric permittivity (ARDP), bulk electrical conductivity (BEC) and temperature data from archaeological features and the surrounding soil matrix (SSM) for four sites over a 16-23 month period. Soil samples were taken to study links between geotechnical and EM properties in the laboratory.

Differences in BEC-VWC (volumetric water content) and ARDP-VWC relationships between fine and coarse grained soils were found, but differences between archaeological and SSM soils were small, confirming field measured contrasts predominantly result from VWC differences. ARDP-VWC relationships were affected by the EM loss tangent rather than just bound water as previously suggested, making BEC and magnetic properties of the soil significant. Both archaeological and SSM soils showed similar trends in recorded values and infiltration responses after rainfall events, and differences were predominantly due to water holding capacities of the soils and variations in drying patterns which were tied to the properties of the soil, especially porosity, clay content and mineralogy. Whilst coarse grained soils showed good EM contrasts throughout, smaller contrasts were found on fine grained soils, with optimum times for detection found during dry conditions when VWC differences were at a maximum and during warm periods where BEC differences were accentuated.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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