Comparison of Near-surface Geophysical Techniques in
Forensic and Archaeological Investigations

Abstract

Near-surface geophysical techniques should be routinely utilised by law enforcement agencies to detect and locate shallowly buried forensic objects, saving manpower and resources. However, there has been little published research on optimum geophysical detection method(s) and configurations beyond metal detectors and high frequency GPR.

This thesis firstly details systematic multi-frequency GPR surveys over simulated clandestine burials of murder victims in a semi-urban environment over a three year monitoring period. Wrapped burials could be detected throughout, though naked burials were more difficult to detect. It is suggested that detection of naked burials is possible within 18 months of presumed burial. 225 MHz frequency GPR antennae were deemed optimal for target detection and 2D profile analysis alone was deemed sufficient to target burials. Surveys conducted between winter and spring were deemed optimal for target detection.

This thesis next presents three U.K. case studies of church graveyards in contrasting burial environments, soil types, burial styles and ages. Geophysical survey results reveal that unmarked burials can be identified using 0.5 m spaced 2D GPR profiles using 225 MHz frequency antennae. Bulk ground electrical surveys showed 1 m probe separations were optimal, with datasets needed ‘de-trending’ to reveal burial positions. Results were highly variable depending upon soil type; very coarse soils severely restricted successful detection of unmarked burials by resistivity. GPR therefore proved optimal, though resistivity data proved equally as useful as GPR in more clay-rich soils. Results, combined with subsequent archaeological investigations, showed targets were significantly different from clandestine burials which are commonly used as analogues in forensic geophysics research.

This thesis finally presented multi-technique geophysical surveys to detect simulated unmarked illegal weapons, explosive devices and arms caches that were shallowly buried within a semi-urban environment test site. The site was then covered with a concrete patio before re-surveying in order to represent a common domestic household garden environment. Results showed that the easily-utilised magnetic susceptibility probe was, surprisingly, optimal for target detection in both semi-urban and patio environments in comparison to all other techniques trialled and, interestingly, compared to other magnetic equipment. Basic metal detector surveys had similar target detection rates though the handgun was not detected. High-frequency (900 MHz) GPR antennae was optimal for target detection in the semi-urban environment whilst 450 and 900 MHz frequencies had similar detection rates in the patio scenario. Resistivity surveys at 0.25 m probe- and sample-spacings were good for target detection in the semi-urban environment. 2D profiles were sufficient for target detection but resistivity datasets required site ‘de trending’ to resolve targets in map view.

Forensic geophysical techniques are shown here to be rapidly evolving to assist search investigators in the detection of hitherto difficult-to-locate buried forensic targets and, as such, further research in this field is suggested.