Decades of military operations have left a legacy of unexploded ordnance (UXO) across the world, including our own countries. These weapons, thrown at the ground during battles and other military operations, remain on the surface, in the subsurface, and underwater, posing a continuing threat to our communities and infrastructure.
UXO presents a serious global threat. Each year, land mines and unexploded ordnance kill or maim an estimated 15,000–25,000 people. Surveyors and construction teams encounter unexploded ordnance in war or conflict zones on land and underwater. These hazards endanger lives and disrupt construction projects, from urban centers to rural areas. They include munitions such as bombs, bullets, and mines dropped during military operations or maintenance and demolition works.
“Modern weapons are estimated to have a failure rate of 5%. Depending on various factors, the failure rate can be up to 40%. Any armed conflict in the world has created, creates, and will create the same problem,” perceive Alexey Dobrovolskiy, Chief Technology Officer at SPH Engineering.
Advancements in UXO Detection Technologies
Although UXO threat is increasing globally, however, survey technologies and clearance methodologies are also improving in line with this threat, allowing for faster, more accurate target identification, environmentally conscientious clearance and the reduction of overall risk to land-based and water-based site projects. Detecting land or underwater UXO is complex and can require well designed surveys with high sensitivity sensors.
“Unexploded ordnance pose significant risks to both human lives and infrastructure development. Ground penetrating radar (GPR) can be an effective tool for locating land-based UXO. GPR can detect objects at various depths, ranging from a few centimeters to several meters, depending on the specific equipment and soil conditions. GPR enables survey teams to detect subsurface anomalies, such as munitions or buried objects, in real-time without the need for excavation, enabling faster and informed decision-making,” comments Allison Annan-Bujold, GPR Product Management Director at Sensors & Software Inc.
Importance of Workflow and Data Quality in UXO Surveys
Managing the process of UXO surveys is important and often involves multiple stakeholders. It can be a costly and time-consuming task. This is where a good workflow and commonly agreed data quality factors are important. This helps project stakeholders understand how the survey will be conducted and what data quality thresholds the sensors must meet to detect a given reference object. It also allows the team to spend more time on data analysis, interpretation and reporting.
UXO Risk Assessment and Survey Planning
With reference to Stephen Wilson, Director of Business Development & UXO Manager at EPI Group, “We always start with a UXO Threat & Hazard Assessment. Covering the project site boundaries and surrounding areas of influence, this is a desk-based study of the UXO history in the area, describing the types, possible condition, and density of UXO that may be present within an area of investigation, where, and why.
“Surveyors assess potential UXO hazards against the planned project operations to determine their likelihood of causing harm to people, equipment, the environment, and species of concern. They conduct a UXO survey only for hazards that pose a risk; if no risks exist, they do not perform a survey. This approach ensures the UXO survey targets actual project risks and allows all project developers to achieve the “As Low As Reasonably Practicable” safety standard in a cost-effective way.”
Data Transparency and Survey Accuracy
As multi-sensor datasets become increasingly large, a well-defined workflow with commonly agreed data quality factors is essential to improve the transparency of both land or water-based UXO surveys and trust in their results. This will help to avoid miscommunications between survey teams, clients and project managers that could lead to expensive delays or even cancellation of a project.
“GPR systems can collect data over a large land area and map the results,” says Allison. “The software enables detailed data visualization, interpretation, and integration with geospatial information systems (GIS), aiding in the creation of UXO hazard maps that accurately represent the land locations, depths, and sizes of potential UXO targets. The mapping capability enables UXO detection teams to prioritize and plan their clearance operations,” she adds.
Importance of UXO Surveys
UXO is a major concern for a wide range of projects, from construction and excavation to wind farm installations, oil exploration, offshore oil & gas platforms and capital dredging. As a result, it is necessary to plan and execute the survey to ensure that any potential hazards are identified prior to any land or sea activities. Detection is the most important aspect of any UXO survey. The aim is to locate, identify and then remove any items that are a threat to any property or people within an area. To achieve this, an expert survey team will need to understand the local environment and the likely threats. This will enable them to recommend the best possible detection method for the site.
Types of UXO Surveys and Methodologies
“UXO surveys are a key part of the management of UXO contamination, management meaning normally to remove the contamination for land release. There are different types of UXO surveys, and the process would depend on the specific situation at different geographic levels. Arguably the most important UXO survey is the Non-Technical Survey (NTS) or desk top survey, normally conducted prior to any planned encounter with UXO contamination, consisting of research and interviews. This would determine areas of priority, non or less contaminated areas, and the type of contamination, which in turn would determine the type of detection equipment needed for ‘on-site’ survey to further confirm the findings of the NTS, and further clearance techniques and technologies required,” remarks Steve Marner, Senior Technical Delivery Manager at Artios Global Ltd.
Environmental and Economic Impact of UXO
According to Wolfgang Suess, Managing Director at SENSYS, the importance of UXO surveys is manifold as buried UXOs in the ground that are leaking over time.
“Chemicals are a threat to our environment and intact ammunition will lead to a lot of collateral damages and injuries or deaths. In order to release mined or contaminated areas to vitalize an economy especially in the areas of agriculture and civil engineering, UXO surveys have to be done addressing 100% of an area.”
“For this kind of survey, an assigned expert will provide (aerial) remote operated or man operated detection systems with Magnetometers or electromagnetic sensors to detect all kind of bombs and ammunition in that particular land area. Additionally, metal and iron free plastic mines have to be detected by more specific devices or in labor intensive man based ground surveys – which by far are the most dangerous processes in demining,” expresses Wolfgang.
“The problem of UXO is not only a problem on land, but in the water as well. Here again, leaking ammunition is harming our marine environment such that, TNT (Trinitrotoluene) and other elements are found in water, fishes and plants,” he adds.
Marine UXO Survey Techniques and Challenges
“There are four general methods for performing a sea based UXO survey. The two most common solutions are towed magnetometer/gradiometer or ROV based gradiometer. In certain scenarios and regions ROV based electromagnetic systems or 3D chirp systems could also be used, however, this is a more uncommon approach. The industry standard towed solution for large scale UXO campaigns today uses one or several remotely operated towed vehicles (ROTV), with an array of magnetometers or gradiometer,” acclaims Thomas Mennerdahl, Technology Director Subsea at Reach Subsea AS.
After a survey campaign and data assessment, surveyors include anomalies characterized as probable UXO (pUXO) in a target list for further investigation to confirm the anomaly. For water-based projects, specialists investigate these targets using UXO ROVs, Explosive Ordnance Disposal (EOD) divers, or a combination of both, depending on water depth and tidal conditions. If specialists deem the UXO ‘viable’ and cannot avoid it, they destroy it in situ or remove it to a suitable disposal site.
“It is best practice for higher risk projects to embark UXO Specialists on site to verify anomalies or not. However, logistical and geographical practicalities, or in lower risk water sites, a remote explosive ordnance identification process can be available. Doing the right UXO survey, looking for the right potential targets based upon the threat assessment, is the most pragmatic way to make your project safe and allow an ALARP (As Low As Reasonably Practicable) certification,” counsels Stephen.
Global Scale of Marine UXO Threat
Vincent van Santen, Business Development Manager Offshore Wind and UXO at Fugro, says, “An estimated 1.3 million tonnes of unexploded ordnance (UXO) scatter the world’s oceans, posing serious threats to safety and marine pollution.”
Historical Context and Risk Factors in Marine Environments
Thomas emphasizes that unexploded ordnance (UXO) in the marine environment poses a significant but variable risk, depending on historical conflicts, military activities, and munitions disposal practices. For example, during World War I and World War II (1848–1946), military forces dropped approximately 150,000 mines and millions of aerial bombs in the Baltic Sea alone. Mines withstand water pressure, and in low-salinity, low-oxygen areas like the Baltic Sea, the steel casings of munitions remain largely intact at deeper depths, leaving UXO inactive but potentially well preserved.
Thomas further explains that, despite extensive mine-hunting and clearance campaigns following the world wars and the fall of the Soviet Union, UXO still presents a risk to marine construction. He recommends that UXO surveys should be based on desktop studies and applied to any seabed-interacting projects, considering the following:
-
Historical Context: Assess historical conflicts, military activities, and disposal campaigns in the area, including past munitions dumping practices. Areas affected by trawling may have UXO displaced randomly, increasing the risk of encountering UXO both within and outside known risk zones.
-
Geographical Location: Evaluate marine environment characteristics such as water depth, seabed composition, currents, sediment movement, and tides, as these factors affect UXO distribution and potential exposure.
Survey Design and Sensor Integration
UXO consultants design surveys that optimize efficiency and ensure high-quality data acquisition to meet the client’s requirements. They often use gradiometers, proton and caesium magnetometers, and high-resolution side scan sonar to achieve this.
Detection Methods from Broadband Electromagnetic Signals
Surveyors conduct UXO surveys to detect metallic objects buried in the ground or lying on the seabed that may relate to unexploded ordnance (UXO) or explosive remnants of war (ERW). The purpose of this study is to introduce an automated anomaly-picking method for detecting metallic objects from broadband electromagnetic signals.
UAV and Electromagnetic Detection Technologies
“Unmanned Aerial Vehicle (UAV) technology allows for the use of broadband frequency domain electromagnetic system for shallow subsurface target detection. The technology allows for determining the range to an object and may be of benefit to detect objects remotely,” articulates Stephen. “Existing ranging technologies can be: susceptible to mutual interference (e.g. traditional sonars on the same frequency band operating at the same time may cause cross interference); not operating continuously (e.g. pulsed), therefore detection of obstacles between pulses is not possible; and operate on a narrow band, which may lead to lack of detections at certain frequencies,” adds Stephen.
Multi-Sensor Data Integration and Processing
This technique combines multibeam Echosounder (MBES) and acoustic survey data with towed magnetometer arrays to produce detailed bathymetry and target localization results. This approach has the advantage of providing a high spatial resolution and the benefit of using only one platform for survey operations.
“UXO survey campaigns are complex with many variables. They frequently combine a variety of different techniques, depending on the site’s particular conditions, the target’s features, and the survey’s goals,” says Vincent. “To achieve reliable and accurate identification of UXO artefacts, automated detection approaches are often combined with human experience and visual confirmation. Multiple detection techniques to identify potential UXO objects can be applies in the seabed, electromagnetic signals being one of them. The latest developments in data processing algorithms can also be used to improve processing time and ensure methods are objective, repeatable and auditable,” he adds.
“The utilisation of this emerging broadband electromagnetic technology could allow for superior detections when compared to most technologies currently available. Stephen observed, “UXO survey techniques aim to produce a master target list of potential pUXO, which surveyors must investigate before ALARP. We must identify all pUXO without adding unnecessary targets to the master list, as investigations are very costly.”
During the initial phase of a technical UXO survey, surveyors deploy a range of sensor methods. This phase requires a deep understanding of the type of munitions, geophysical survey methods, data processing and management skills.
Innovative technologies for UXO surveys
When it comes to best technologies for land-based UXO surveys, Allison affirms that Ground Penetrating Radar is complementary to other detection methods. “GPR uses low energy, high frequency radio waves to image metallic and non-metallic objects in the subsurface, making it a natural technology to use for locating buried UXO. There is a wide selection of GPR systems and configurations available, making GPR adaptable to different terrains for UXO applications”, she adds.
Magnetometer Challenges and Solutions
Moreover, magnetometers experience systematic errors caused by the sensor itself and the magnetic environment in which they operate. Hard and soft iron effects, zero bias errors, scale factors, and non-orthogonality induce these errors, which appear as orientation- and movement-induced noise in the measured total magnetic field. The sources of these magnetic influences are the sensor, the sensor platform and the surface vessel (in shallow water); this is with regards to Thomas.
ROV-Based Detection Systems
“In the late 2000s, researchers introduced ROV-based gradiometer systems, which offer advantages but also pose some challenges. Magnetometers that measure the total field become complicated to use on ROVs because the motion of the ROV or vessel induces noise, which alters the measured magnetic field,” he adds.
Thomas also notes, “The main solution involves using two or more magnetometers in a gradiometer configuration. In this setup, the surface vessel affects all sensors equally due to the relative distance between the ROV and the vessel and the spacing between the magnetometers in the array. As this is not the case for the targets located on the seabed, this method does not suppress any data of interest in an archaeological or sea based UXO survey.”
Advanced Detection Solutions for Complex Environments
“When there is a risk for non-ferrous UXOs or there are subsea structures and/or geology/boulders that could mask the magnetic signature of a possible UXO target a ROV based electromagnetic system or 3D chirp system can be an appropriate solution. In shallow water the 3D chirp could be fitted to the surface vessel without requirement for ROV or towed solutions,” adds Thomas.
Selecting the Right UXO Technology
“Once authorities determine the need to enter a UXO-contaminated area for survey or clearance, they consider factors to select the most suitable and practical technologies or techniques. For example, the most up to date third generation detection equipment may not be suitable for very simple small-scale contamination; or time and speed of clearance may be the precedence over cost of such high-end technologies (and techniques such as mechanical clearance with armoured earth moving machines)” clinches Steve.
Future of UXO Detection Technologies
In recent decades, developers have created numerous new and innovative technologies to improve UXO detection. These include digital geophysics and a combination of electromagnetic sensors. Combined with data analysis workflows, these technologies can greatly improve the accuracy of locating UXOs.
Read More:
