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Semblance analysis to assess GPR data from a five-year forensic study of simulated clandestine graves

Booth, Adam D.; Pringle, Jamie K.

Semblance analysis to assess GPR data from a five-year forensic study of simulated clandestine graves Thumbnail


Authors

Adam D. Booth



Abstract

Ground penetrating radar (GPR) surveys have proven useful for locating clandestine graves in a number of forensic searches. There has been extensive research into the geophysical monitoring of simulated clandestine graves in different burial scenarios and ground conditions. Whilst these studies have been used to suggest optimum dominant radar frequencies, the data themselves have not been quantitatively analysed to-date. This study uses a common-offset configuration of semblance analysis, both to characterise velocity trends from GPR diffraction hyperbolae and, since the magnitude of a semblance response is proportional to signal-to-noise ratio, to quantify the strength of a forensic GPR response. 2D GPR profiles were acquired over a simulated clandestine burial, with a wrapped-pig cadaver monitored at three-month intervals between 2008-2013 with GPR antennas of three different centre-frequencies (110, 225 and 450 MHz). The GPR response to the cadaver was a strong diffraction hyperbola. Results show, in contrast to resistivity surveys, that semblance analysis show little sensitivity to changes attributable to decomposition, and only a subtle influence of seasonality: velocity increases (0.01-0.02 m/ns) were observed in summer, associated with a decrease (5-10%) in peak semblance magnitude, SM, and potentially in the reflectivity of the grave. The lowest-frequency antennas consistently gave the highest signal-to-noise ratio although the grave was nonetheless detectable by all frequencies trialled. This therefore suggests forensic radar surveys should be undertaken without regard to seasonality. Whilst GPR analysis cannot currently provide a quantitative diagnostic proxy for time-since-burial, the consistency of responses suggests that graves will remain detectable beyond the five years shown here.

Citation

Booth, A. D., & Pringle, J. K. (2016). Semblance analysis to assess GPR data from a five-year forensic study of simulated clandestine graves. Journal of Applied Geophysics, 125, 37-44. https://doi.org/10.1016/j.jappgeo.2015.11.016

Journal Article Type Article
Acceptance Date Nov 27, 2015
Online Publication Date Dec 19, 2015
Publication Date 2016-02
Publicly Available Date May 26, 2023
Journal Journal of Applied Geophysics
Print ISSN 0926-9851
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 125
Pages 37-44
DOI https://doi.org/10.1016/j.jappgeo.2015.11.016
Keywords forensic search, clandestine grave, GPR, semblance analysis
Publisher URL http://dx.doi.org/10.1016/j.jappgeo.2015.11.016

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