UXO Surveys – The best innovative UXO detecting technology methods

Decades of military operations have left a legacy of unexploded ordnance (UXO) across the world, including our own countries. These weapons, which were thrown at the ground during battles and other military operations, are still present on the ground, in the subsurface and underwater, and remain a threat to our communities and our infrastructure.

The threat of UXO is a global and serious issue. It is estimated that around 15,000-25,000 people are killed or maimed by land mines and UXO each year. Unexploded ordnance is a hazard that can be found in any war or conflict area either on land or underwater. They can be dangerous and cause significant disruption to a land or sea construction sites, from urban centres to rural areas. These include munitions like bombs, bullets and mines that were dropped during the maintenance or 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.

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.

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 can make it easier for project stakeholders to understand how a survey will be conducted, and what data quality thresholds are expected from the sensors used in order to detect a given reference object. It also allows the team to spend more time on data analysis, interpretation and reporting.

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. These potential UXO hazards are then risk assessed against the planned project operations for their likelihood to cause harm to people, plant, environment and species of concern. Only those potential UXO that pose a risk need to be the subject of a UXO survey, if there are no risks identified, no survey is required. This ensures the UXO survey is specific to managing the actual project risks and that the “As Low As Reasonably Practicable” safety methodology, is a viable cost-effective solution that can be reached by all project developers.”

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.

“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.

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.

“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.

“Following a survey campaign and data assessment and anomalies characterised as probable UXO (pUXO), will be included in a target list to be further investigated to positively identify the anomaly. Typically, for water based projects, this is undertaken by specialist UXO ROVs or Explosive Ordnance Disposal (EOD) divers, or a mixture of both depending on water depth and tidal effects. If the UXO is considered ‘viable’ and it is not possible to avoid the identified UXO, then normally it should be destroyed in situ or removed 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.

“The world’s oceans are scattered with an estimated 1.3 million tonnes of unexploded ordnance (UXO) – hidden dangers that pose a serious threat to safety and marine pollution,” says Vincent van Santen, Business Development Manager Offshore Wind and UXO at Fugro.

On the other hand, expressing his opinion, Thomas, signifies that, Unexploded ordnance (UXO) in the marine environment presents a significant but varying risk depending on historical conflicts, military activities, and munitions disposal practices. For example during World War I and World War II in the years 1848 – 1946 approximately 150 000 mines and millions of aerial bombs were dropped only in the Baltic Sea. Mines are constructed to endure the water pressure. In waters where the salinity and oxygen levels in general are very low, such as the Baltic Sea, the munitions steel casing can be more or less intact at deeper water depths leaving the UXO inactive but potentially still well preserved.

Thomas further go into detail that, even though there has been significant mine hunting and clearance campaigns following the world wars and the fall of Soviet Union, UXO remains a risk to marine construction. The requirement for UXO surveys should be based on desktop studies and is recommended for any seabed-interacting projects taking the following into consideration:
• Historical Context: Assess the historical conflicts, military activities, and disposal campaigns in the area. This shall also include past practices of dumping munitions at specific sites. Where trawling is a fact there is a risk of UXOs being displaced randomly increasing the risk to encounter UXO in the vicinity and potentially outside what is considered a risk area.
• Geographical Location: Evaluate the specific characteristics of the marine environment. Factors such as water depth, seabed composition, currents, sediment movement, and tides can impact the distribution and potential exposure to UXO.

UXO consultants generate survey designs that are optimised for efficiency and high quality data acquisition in order to meet the client’s requirements. This is often achieved through the use of gradiometers; proton and caesium magnetometers in conjunction with high resolution side scan sonar.

Detection Methods from Broadband Electromagnetic Signals

UXO surveys are conducted to detect metallic objects that may have been buried in the ground or present on the seabed and that are believed to be related 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.

“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.

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. The purpose of UXO survey techniques is to produce a master target list of potential pUXO, which will need to be investigated prior to ALARP. It is imperative that we do not miss pUXO and that we do not unnecessarily add pUXO to the master target list, as investigation is a very expensive process,” observed Stephen.

During the initial phase of a technical UXO survey, a range of different sensor methods are deployed. 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.

Moreover, magnetometers are subject to systematic errors inherent to the sensor itself and the magnetic environment it is placed in. These errors are induced by hard and soft iron effects, zero bias errors, scale factors and non-orthogonality- which will show up as an orientation- and movement induced noise on 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.

“In late 2000s ROV based gradiometer systems were introduced which has advantages but also some challenges. The main reason why magnetometers measuring total field are very complicated to use on ROVs, is due to the noise induced by the motion of the ROV/vessel in relation to the magnetometer which will change the measured magnetic field,” he adds. Additionally, Thomas is certain that, “The main solution to this is the use of two or more magnetometers in a gradiometer configuration. In such a setup, the influence on the total field from the surface vessel is assumed to be equal on all sensors due to the relative distance between the ROV and the surface vessel, and the distance 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.”

“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.

“Once the fact that intervention into a UXO contaminated area, for survey or clearance, is determined, factors have to be taken into consideration for the best suited and most practicable technologies or techniques required. 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.

In recent decades, a number of new and innovative technologies have been developed to improve the detection of UXOs. 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.