The application of low-altitude near-infrared aerial photography for detecting clandestine burials using a UAV and low-cost unmodified digital camera

Monitoring of simulated clandestine graves of victims using UAVs, GPR, electrical tomography and conductivity over 4-8 years post-burial to aid forensic search investigators in Colombia, South America

In Colombia there are estimated to be over 121,000 missing people and victims of forced disappearances. Forensic investigators therefore need assistance in determining optimal detection techniques for buried victims, to give victims' families closure and for the wider community to see that justice is being served. Previous research has created 12 controlled simulated clandestine graves of typical Colombian murder victim scenarios at 0.5 m - 1.2 m depths in savannah and rainforest sites in Colombia. The 0-3 years of geophysical monitoring results of were published, with this paper reporting on 4-8 years monitoring of both UAV drone results and geophysical data. The UAV results from the year 8 survey, published for first time from Colombia, showed that the simulated graves could still be located using NDVI and NIR multi-spectral data, but not using optical or other multi-spectral data. The 0-3 years of geophysical data found the simulated clandestine graves could be detected with electrical resistivity and GPR methods, with the 4-8 year surveys evidencing that they could still be detected using bulk ground conductivity surveys, GPR horizontal time slice datasets and 2D ERT profiles. Research implications suggest initial use of UAV remote sensing technology to pinpoint likely search areas, before subsequent ground reconnaissance, geophysical surveys and their interpretation, before intrusive investigation methods are employed for detecting missing and disappeared persons in Colombia.

The suitability of using domestic pigs (Sus spp.) as human proxies in the geophysical detection of clandestine graves

Research in many forensic science fields commonly uses domestic pigs (Sus spp.) as proxies for human remains, due to their physiological and anatomical similarities, as well as being more readily available. Unfortunately, previous research, especially that which compares the decompositional process, has shown that pigs are not appropriate proxies for humans. To date, there has not been any published research that specifically addresses whether domestic pigs are adequate human proxies for the geophysical detection of clandestine graves. As such, the aim of this paper was to compare the geophysical responses of pig cadavers and human donor graves, in order to determine if pigs can indeed be used as adequate human proxies. To accomplish this, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) responses on single and multiple pig cadaver graves were compared to single and multiple human donor graves, all of which are in known locations within the same geological environment. The results showed that under field conditions, both GPR and ERT were successful at observing human and pig burials, with no obvious differences between the detected geophysical responses. The results also showed that there were no differences in the geophysical responses of those who were clothed and unclothed. The similarity of the responses may reflect that the geophysical techniques can detect graves despite what their contents are. The study implications suggest that experimental studies in other soil and climate conditions can be easily replicated, benefiting law enforcement with missing persons cases.

The second near-infrared fluorescence concealed imaging for identifying smuggled baggage

Smuggling methods are renovating with more diversified, complicated means, thereby developing concealed and non-sensitive luggage identification technology is of great significance. Herein, for the first time, the second near-infrared (NIR-II, 1000-2500 nm) concealed imaging for identifying smuggled baggage based on organic small molecule luminescent material was studied. A small molecule luminescent material (Y6) with the excitation in invisible near-infrared (NIR) light was used to generate fluorescence-emission in NIR-II region. The traceless Y6 sprayed on the surface of criminal luggage does not emit light under visible light irradiation, but shows hidden NIR-II signs under NIR excitation that can prevent the suspects to find abnormality and lose their luggage. The Y6 organic luminescent material has invisibility, low toxicity, long-term fluorescence stability and high transparency. This NIR-II fluorescence imaging technology can be used as a new type of concealed baggage marking, which is of great significance to help the customs combat smuggling crimes.

Design of Airborne Large Aperture Infrared Optical System Based on Monocentric Lens

Conventional reconnaissance camera systems have been flown on manned aircraft, where the weight, size, and power requirements are not stringent. However, today, these parameters are important for unmanned aerial vehicles (UAVs). This article provides a solution to the design of airborne large aperture infrared optical systems, based on a monocentric lens that can meet the strict criteria of aerial reconnaissance UAVs for a wide field of view (FOV) and lightness of airborne electro-optical pod cameras. A monocentric lens has a curved image plane, consisting of an array of microsensors, which can provide an image with 368 megapixels over a 100° FOV. We obtained the initial structure of a five-glass (5GS) asymmetric monocentric lens with an air gap, using ray-tracing and global optimization algorithms. According to the design results, the ground sampling distance (GSD) of the system is 0.33 m at 3000 m altitude. The full-field modulation transfer function (MTF) value of the system is more than 0.4 at a Nyquist frequency of 70 lp/mm. We present a primary thermal control method, and the image quality was steady throughout the operating temperature range. This compactness and simple structure fulfill the needs of uncrewed airborne lenses. This work may facilitate the practical application of monocentric lens in UAVs.

UAV-assisted real-time evidence detection in outdoor crime scene investigations

Nowadays, a plethora of unmanned aerial vehicles (UAVs) designs that significantly vary in size, shape, operating flight altitude, and flight range have been developed to provide multidimensional capabilities across a wide range of military and civil applications. In the field of forensic and police applications, drones are becoming increasingly used instead of helicopters to assist field officers to search for vulnerable missing persons or to target criminals in crime hotspots, and also to provide high‐quality data for the documentation and reconstruction of the forensic scene or to facilitate evidence detection. This paper aims to examine the contribution of UAVs in real‐time evidence detection in outdoor crime scene investigations. It should be highlighted that the project innovates by providing a quantitative comparative analysis of UAV‐based and traditional search methods through the simulation of a crime scene investigation for evidence detection. The first experimental phase tested the usefulness of UAVs as a forensic detection tool by posing the dilemma of humans or drones. The second phase examined the ability of the drone to reproduce the obtained performance results in different terrains, while the third phase tested the accuracy in detection by subjecting the drone‐recorded videos to computer vision techniques. The experimental results indicate that drone deployment in evidence detection can provide increased accuracy and speed of detection over a range of terrain types. Additionally, it was found that real‐time object detection based on computer vision techniques could be the key enabler of drone‐based investigations if interoperability between drones and these techniques is achieved.

Stray Light Analysis and Elimination of an Optical System Based on the Structural Optimization Design of an Airborne Camera

An aspherical airborne camera has excellent performance in the field of photoelectric reconnaissance equipment. However, the image plane contrast of the optical system will be reduced by stray light originating from inside or outside of the optical system. In the present work, the self-designed aspheric airborne camera is manufactured with a baffle and vanes to reduce the impact of stray light on the camera imaging quality. TracePro software is used to analyze the stray light and establish an ABg mathematical model based on the scattering intensity measurement. The incident angle of the light parallel to the optical axis is set, and ray tracing is performed on the optical machine model to verify whether it conforms to the optical system design. The results showed that when the incident angle of the light source is greater than 0.5°, the point source transmittance (PST) value drops rapidly, and when the incident angle is 30°, the PST value of the system is in the order of 10−8. Stray light analysis verifies that the self-designed aspheric surface-based camera optomechanical structure has the ability to suppress stray light. The design of the baffle and vanes further enhances the ability of the optical system to suppress stray light, which can provide a reference for the design of a stray light elimination structure.

Monitoring of simulated clandestine graves of dismembered victims using UAVs, electrical tomography, and GPR over one year to aid investigations of human rights violations in Colombia, South America

In most Latin American countries, there are significant numbers of missing people and forced disappearances, over 120,000 in Colombia alone. Successful detection of shallow buried human remains by forensic search teams is difficult in varying terrain and climates. Previous research has created controlled simulated clandestine graves of murder victims to optimize search techniques and methodologies. This paper reports on a study on controlled test site results over four simulated dismembered victims' clandestine graves as this is sadly a common scenario encountered in Latin America. Multispectral images were collected once post-burial, electrical resistivity surveys were collected 4 times, and ground penetrating radar (GPR) surveys were collected three times up to the end of the 371 day survey monitoring period. After data processing, results showed that the multispectral data set could detect the simulated clandestine and control graves, with electrical resistivity imaging relative high resistances over some of the simulated graves but not over the empty control graves. GPR results showed good imaging on the Day 8 surveys, medium imaging on the Day 294 surveys, and medium to good imaging on the Day 371 surveys. Study implications suggest that, while clandestine graves of dismembered homicide victims would likely result in smaller-sized graves when compared to graves containing intact bodies, these graves can still potentially be detected using remote sensing and geophysical methods.

Autonomous Service Drones for Multimodal Detection and Monitoring of Archaeological Sites

Constant detection and monitoring of archaeological sites and objects have always been an important national goal for many countries. The early identification of changes is crucial to preventive conservation. Archaeologists have always considered using service drones to automate collecting data on and below the ground surface of archaeological sites, with cost and technical barriers being the main hurdles against the wide-scale deployment. Advances in thermal imaging, depth imaging, drones, and artificial intelligence have driven the cost down and improved the quality and volume of data collected and processed. This paper proposes an end-to-end framework for archaeological sites detection and monitoring using autonomous service drones. We mount RGB, depth, and thermal cameras on an autonomous drone for low-altitude data acquisition. To align and aggregate collected images, we propose two-stage multimodal depth-to-RGB and thermal-to-RGB mosaicking algorithms. We then apply detection algorithms to the stitched images to identify change regions and design a user interface to monitor these regions over time. Our results show we can create overlays of aligned thermal and depth data on RGB mosaics of archaeological sites. We tested our change detection algorithm and found it has a root mean square error of 0.04. To validate the proposed framework, we tested our thermal image stitching pipeline against state-of-the-art commercial software. We cost-effectively replicated its functionality while adding a new depth-based modality and created a user interface for temporally monitoring changes in multimodal views of archaeological sites.

Assessing optical remote sensing for grave detection

The application of an effective and ready-to-use tool for discovering clandestine graves is crucial for solving a number of cases where disappearance of people is involved. This is the case in Mexico, where the government drug war has resulted in a large number of missing people that has been estimated to be over 40,000 since the year 2006. In this article, we report results from an experimental study on simulated animal graves detection using several techniques from optical remote sensing. Results showed that several spectral indices from hyperspectral and/or multispectral sensors may be used to detect N-enriched vegetation. Thermal imagery was also effective to detect underground voids through differential thermography, although this was only effective for detecting large graves with bare terrain. Lastly, while dense pointclouds reconstructed from oblique aerial photography was able to detect vegetation regrowth over the pits, the terrain subsidence was not sufficiently large to be detected with this technique, even in the case of mechanical removal of vegetation.

Application of viewshed analysis and probability mapping for search area determination based on the Moors murders on Saddleworth Moor, the United Kingdom

Geographical Information System (GIS) is underutilized within the forensic discipline, especially concerning the discovery of clandestine graves. GIS, viewshed analysis, and probability maps are being introduced into desk-based research both for archaeology and forensic purposes. This study aims to investigate how useful GIS can be to narrow down large search areas when locating clandestine graves. Combining GIS, viewshed analysis, and probability maps allows for the exploration of potential areas of concealment and diggability on Saddleworth Moor to find the remaining missing Moors victim, Keith Bennett. Methods included viewshed analysis consisting of what is visible and not visible from a certain location while the probability map registers the likelihood of penetrability across the Moors landscape. Using two GIS software programs, QGIS and ArcGIS Pro, maps were constructed examining the A635 on Saddleworth Moor and the potential location of Keith Bennett. This takes into consideration the geology, terrain, water networks, and road systems. Analysis of the GIS maps demonstrated that two possible areas were likely to be able to conceal Keith Bennett's body. It then aids to identify areas for further investigation. This study also indicates that GIS data analysis has the potential to aid in criminal and civil investigations and helps narrow down search areas to manageable sizes. Not only does it aid in cold case criminal investigations but it can also be utilized within everyday desk-based research on recent investigations.

3D Reconstruction and Geostatic Analysis of an Early Medieval Cemetery (Olonne-sur-Mer, France)

A preventive excavation performed in 2018 prior to development work led to the discovery of more than 213 subjects buried from the 4th to the 11th centuries in the 1850 m2 dug area. This is a cemetery located in Olonne-sur-Mer in France (46.53723, −1.77603). The complex is limited to the south by a ditch. To the north, no limits were observed during the excavation and, to the west, ancient archaeological surveys suggest an extension of the burial area. Biological analysis of the skeletons reveals a demographic characterizing a natural community, with an under-representation of children under 5 and with subjects under 20 appearing to be grouped together in the center of the area. The place where the youngest are buried often testifies to a strategic position in Christian contexts (near church doors, under sub stillicidio gutters, etc.). Funeral practices are characterized by numerous skeletal alterations, especially in the western area of the site where their concentrations are particularly significant. These are not ossuaries but rather supernumerary bones present in the fills of graves of subjects in place or old tombs where no skeletons in place are preserved. These alterations mark the areas where burials are most frequent. The 3D reconstruction is coupled with geostatistical analyses (heatmap and Moran’s index), considering the digging of the land, the concentration of residual artefacts found in the graves, but also the biological characteristics of the sample and the funeral practices uncovered. From 2D entities generated with GIS software, the process of the elevation and sculpture of the volumes is innovative, because even if it is carried out by precise but classical computer graphics techniques, it is led by advanced taphonomical and anthropological reflections. This makes it possible to propose empty spaces, a potential gathering area for the village community and circulation paths. These elements are essential in order to go beyond the storytelling often proposed in archaeology and propose a vision based on the coherence of the observed facts. Even when the archaeological remains are only sunken (no preserved elevation), the integration of multisource archaeological data (biological anthropology, funerary, artefacts and pit size) allows relevant 3D reconstructions as a formidable tool for discussing past occupations. Three-dimensional technologies make it possible to recreate a lost environment to allow a better understanding of the site. They are didactic and help to share data between researchers and/or the public, especially when they are invisible such as the presence of empty space.

Sensor Information Sharing Using a Producer-Consumer Algorithm on Small Vehicles

There are several tools, frameworks, and algorithms to solve information sharing from multiple tasks and robots. Some applications such as ROS, Kafka, and MAVLink cover most problems when using operating systems. However, they cannot be used for particular problems that demand optimization of resources. Therefore, the objective was to design a solution to fit the resources of small vehicles. The methodology consisted of defining the group of vehicles with low performance or are not compatible with high-level known applications; design a reduced, modular, and compatible architecture; design a producer-consumer algorithm that adjusts to the simultaneous localization and communication of multiple vehicles with UWB sensors; validate the operation with an interception task. The results showed the feasibility of performing architecture for embedded systems compatible with other applications managing information through the proposed algorithm allowed to complete the interception task between two vehicles. Another result was to determine the system’s efficiency by scaling the memory size and comparing its performance. The work’s contributions show the areas of opportunity to develop architectures focusing on the optimization of robot resources and complement existing ones.

Drone aerial imagery for the simulation of a neonate burial based on the geoforensic search strategy (GSS)

A woman reporting the homicide and burial of an infant in 2004 prompted the creation of an experimental simulated neonate grave shortly before the real search commenced. The real case, documented here, did not use aerial imagery, but used ground-penetrating radar (calibrated to the test site described here) to identify two locations that were probed for gas release and the deployment of victim recovery dogs. We suggest technological advances in remotely sensed aerial imagery that have developed since 2004 will demonstrate their use in focusing such searches by informing a Geoforensic Search Strategy (GSS) and suggesting locations accessible by a perpetrator to identify a burial location using the still-existent analogue site. To test this, in the spring of 2020 a DJI Mavic Pro drone was flown over the control site containing the simulated 2004 burial. Aerial image processing included the creation of orthomosaics, Normalised Difference Vegetation Index (NDVI), Visual Atmospheric Resistance Index (VARI), and photogrammetry. Conventional ground-based geophysical surveys using ground-penetrating radar, guided by this new type of information integrated into the GSS, confirmed that anomalies seen in drone data were the 16-year-old burial. We test this strategy using both the original simulated burial in Northern Ireland and further evaluate it in two recent simulated graves in the United States in more complex scenarios, but with successful results.

UAS-Based Archaeological Remote Sensing: Review, Meta-Analysis and State-of-the-Art

Over the last decade, we have witnessed momentous technological developments in unmanned aircraft systems (UAS) and in lightweight sensors operating at various wavelengths, at and beyond the visible spectrum, which can be integrated with unmanned aerial platforms. These innovations have made feasible close-range and high-resolution remote sensing for numerous archaeological applications, including documentation, prospection, and monitoring bridging the gap between satellite, high-altitude airborne, and terrestrial sensing of historical sites and landscapes. In this article, we track the progress made so far, by systematically reviewing the literature relevant to the combined use of UAS platforms with visible, infrared, multi-spectral, hyper-spectral, laser, and radar sensors to reveal archaeological features otherwise invisible to archaeologists with applied non-destructive techniques. We review, specific applications and their global distribution, as well as commonly used platforms, sensors, and data-processing workflows. Furthermore, we identify the contemporary state-of-the-art and discuss the challenges that have already been overcome, and those that have not, to propose suggestions for future research.

A Low Cost Approach to Disturbed Soil Detection Using Low Altitude Digital Imagery from an Unmanned Aerial Vehicle

Until recently, clandestine burial investigations relied upon witness statements to determine target search areas of soil and vegetation disturbance. Due to this, remote sensing technologies are increasingly used to detect fresh clandestine graves. However, despite the increased capabilities of remote sensing, clandestine burial searches remain resourcefully intensive as the police have little access to the technology when it is required. In contrast to this, Unmanned Aerial Vehicle (UAV) technology is increasingly popular amongst law enforcement worldwide. As such, this paper explores the use of digital imagery collected from a low cost UAV for the aided detection of disturbed soil sites indicative of fresh clandestine graves. This is done by assessing the unaltered UAV video output using image processing tools to detect sites of disturbance, therefore highlighting previously unrecognised capabilities of police UAVs. This preliminary investigation provides a low cost rapid approach to detecting fresh clandestine graves, further supporting the use of UAV technology by UK police.