Comparison of GPR signals over simulated clandestine graves with domestic pigs (Sus Scrofa domesticus) and human remains.

Studies assessing the use of ground-penetrating radar (GPR) for locating unmarked human graves commonly use pigs as proxies, with recent concerns about the adequacy of pigs as substitutes for humans. Also, there is little agreement on how to identify and describe GPR signals associated with graves. Hence, this project's aim is to compare GPR signals acquired over simulated clandestine graves with pig and human remains. We established human, pig, and control graves at the REST[ES] human decomposition facility in May 2022 and monitored the graves over 17 months using a 250 MHz antenna GPR system. Our results showed the presence of perturbed and V-shaped reflectors, diffraction hyperbolas, and reflectors with amplitude loss at depth between 0.6 and 0.75 m in the radargram for graves with human and pig remains. We corroborate recent studies which concluded that the use of proxies is a viable alternative to human cadavers. The observed radar signatures were classified into five key patterns, which are characteristic of similar data collected with 250 MHz above graves reported in the literature. These classes are: V-shaped dipping reflections from grave walls (class A), small hyperbolic reflections superimposed onto a near-linear reflector (class B), hyperbolic reflections from remains within the grave (class C), new high-amplitude reflection patterns (class D) and significant loss or interruption of reflections (class E). Our proposed classification can help streamline future investigations where the goal is to interpret burials within large GPR datasets and provide language to communicate these results to the broader scientific community.

Self-potential time series reveal emergent behavior in soil organic matter dynamics.

The active cycling of carbon between soil organic matter and the atmosphere is of critical importance to global climate change. An extensive body of research exists documenting the capricious nature of soil organic matter (SOM) dynamics, which is symptomatic of an intricate network of interactions between diverse groups of heterotrophic microorganisms, complex organic substrates, and highly variable local environmental conditions. These attributes are consistent with elements of complex system theory and the temporal evolution of otherwise unpredictable patterns of behavior that emerge from long range dependency on initial conditions. Here we show that vertical depth profile of self-potential (SP) time series measurements responds in a quantitative manner to variations in soil moisture, SOM concentrations, and relative rates of microbial activity. Application of detrended fluctuation analysis (DFA) of self potential time series data is shown additionally to reveal the presence of long-range dependence and emergence of anomalous electrochemical diffusion behavior, both of which diminish with depth as SOM specific energy densities decline.

Geophysical imaging of buried human remains in simulated mass and single graves: Experiment design and results from pre-burial to six months after burial.

In this study, we present an experiment design and assess the capability of multiple geophysical techniques to image buried human remains in mass and individual graves using human cadavers willingly donated for scientific research. The study is part of a novel, interdisciplinary mass grave experiment established in May 2021 which consists of a mass grave with 6 human remains, 3 individual graves and 2 empty control graves dug to the same size as the mass grave and individual graves. Prior to establishing the graves, we conducted background measurements of electrical resistivity tomography (ERT), electromagnetics (EM), and ground penetrating radar (GPR) while soil profiles were analyzed in situ after excavating the graves. All graves were also instrumented with soil sensors for monitoring temporal changes in soil moisture, temperature, and electrical conductivity in situ. Measurements of ERT, EM and GPR were repeated 3, 37, 71 and 185 days after burial with further repeated measurements planned for another twelve months. ERT results show an initial increase in resistivity in all graves including the control graves at 3 days after burial and a continuous decrease thereafter in the mass and individual graves with the strongest decrease in the mass grave. Conductivity distribution from the EM shows a similar trend to the ERT with an initial decrease in the first 3 days after burial. Distortion in linear reflectors, presence of small hyperbolas and isolated strong amplitude reflectors in the GPR profiles across the graves is associated with known locations of the graves. These initial results validate the capability of geoelectrical methods in detecting anomalies associated with disturbed ground and human decay while GPR though show some success is limited by the geology of the site.

Gradient magnetometer dataset and MATLAB numerical code for simulating buried firearms at a controlled field site.

Magnetic survey using multiple magnetometers to obtain gradiometric data can be used as a non-destructive method to search for buried firearms. We present magnetic dataset collected above a set of weapons buried at 0.6 m, 1.2 m, and 1.8 m depths. We provide three datafiles: two datafiles were collected on a coarse grid (1 m by 0.5 m) before and after burial of the weapons, and a third one collected on a fine grid (0.25 m by 0.1 m) after the burial of the weapons which concentrates on the area of buried firearms. We used a Gem Systems GSM-19GW Overhauser gradiometer consisting of two sensors with a relative vertical separation of 55 cm. Data acquisition was done via non-automated point measurements within a gridded measurement domain with data collection locations managed using measurement tape. Each field campaign resulted in about 3,000 data points. In addition, we developed a set of MATLAB scripts to model the magnetic anomalies (total field and gradient) for buried firearms, this set is also included here. The data and modeling scripts relate to a research article published in Forensic Science International (Deng et al., Suitability of magnetometry to detect clandestine buried firearms from a controlled field site and numerical modeling [1]). The dataset may be helpful for testing new algorithms for weapons detection while the numerical codes can be modified and applied for simulating magnetic anomalies resulting from similar buried objects with potential application in the sub-disciplines of forensic and archaeological geophysics.

Suitability of magnetometry to detect clandestine buried firearms from a controlled field site and numerical modeling.

The detection of buried firearms remains a critical issue in law enforcement. We assess the suitability of magnetic gradiometers to detect buried rifles and handguns at multiple depths using numerical modeling and field investigations. Our simulation is based on a simple approach to characterize handguns and rifles as long magnetic dipoles with the firearm characterized by its magnetization, length, centre, azimuth and plunge which allows us to calculate their total magnetic field and gradient anomalies. We compare these synthetic data to field gradiometer data collected with a Gem Systems GSM-19GW Overhauser magnetometer at a field site near Toronto, Canada, where six firearms are buried. Our field magnetometer consists of two sensors with a relative vertical sepration of 0.55 m. We measure the largest anomaly (+/-20 nT) for a rifle at 0.6 m depth, and the smallest anomaly (+/-2 nT) for a handgun buried at 1.8 m depth. The measured anomalies spatially coincide with the locations of weapons while dipole anomalies align along the orientation of the firearms. Our modeling results show that vertically buried weapons produce significantly stronger anomalies than horizontal ones, and even slight tilts enhance the anomalies. We recommend a 0.25 m grid spacing to search for weapons using magnetometry. Our study shows that a range of firearms buried up to 1.8 m can be detected, suggesting that gradient magnetometers are useful tools in forensic weapon searches.