The Science of Magnetometry: Uncovering UXO with Precision

Unexploded ordnance (UXO) can have widespread social, economic, and environmental impacts on the areas it contaminates. These remnants of past conflicts are buried beneath the surface, lying in wait, and often in locations that are now peaceful and thriving communities.

Detecting and safely removing these hazardous items requires tried and tested technologies, and one of the most effective techniques for locating UXO is magnetometry.

In this blog, we are exploring the science of magnetometry and its crucial role in UXO detection.

What is Magnetometry?

Magnetometry is a fundamental technique that measures the Earth’s magnetic field, its strength, and variations caused by the presence of ferromagnetic materials. These variations, or anomalies, can indicate the presence of objects such as iron, steel, and other magnetic materials buried beneath the surface.

Magnetometry is used in a wide range of scientific and practical domains, including archaeology, aviation, oil and gas exploration, defence, pipeline monitoring and UXO detection.

In the context of UXO detection, we use magnetometry to identify the magnetic signatures of unexploded ordnance, allowing for the precise mapping and subsequent safe removal of items of ordnance hidden beneath the surface.

In the UK, UXO contamination can come from a range of sources including Allied munitions from military training, weapons manufacturing, defence activities and WWII airdropped munitions. It is estimated that 10% of WWII German bombs failed to detonate, resulting in widespread UXO contamination across the country, particularly in and around UK cities and industrial areas.

The Science Behind Magnetometry

The Earth’s Magnetic Field

The Earth acts like a giant magnet, with its magnetic field generated by the movement of molten iron within its outer core. This magnetic field is relatively uniform, but local variations occur due to the presence of magnetic minerals in the Earth’s crust. When ferromagnetic objects, such as UXO, are present, they create distinct anomalies in the magnetic field that can be detected and analysed.

Magnetometer Instruments

Magnetometers are instruments designed to measure the strength and direction of the magnetic field at a specific location.

These devices have been around for a long time, with the first magnetometer being produced in 1833. One of the most obvious examples of a magnetometer is a compass.

At Brimstone we use magnetometry in a range of applications:

• Intrusive UXO Surveys – Our Intrusive UXO Surveys are undertaken using a CPT Rig. These rigs use hydraulic pressure to push a magnetometer probe into the ground to survey a column of soil. The probe can identify if there are fluctuations caused by ferrous metals, which could be unexploded ordnance.
• Non-Intrusive Surveys – Our Non-Intrusive UXO Surveys involve us passing magnetometer sensors over the ground in either a pushed, towed or aerial format to detect ferrous materials and map magnetic signatures. This methodology allows us to pinpoint potential items of ordnance without having to disturb the ground.
• Borehole Support – When clearing borehole positions, our teams will use a down-hole magnetometer probe to clear the positions as they get progressively deeper. The engineer will lower the probe to the bottom of the borehole and test for any magnetic signatures within a 1 metre radius. Once cleared, the drilling team are free to advance the next metre. We continue this process, scanning and drilling at 1 metre intervals until we reach the calculated maximum bomb penetration depth of 12 metres.

The Process of Detecting UXO

Picking the Best Methodology

The first step in using magnetometry for UXO detection is carefully selecting the correct methodology. Our team will look at the site in question and enquire about the proposed ground intrusion activities to understand if an Intrusive Survey, Non-Intrusive Survey or Borehole Support is required. The goal is to ensure comprehensive coverage and high-resolution data collection in the most suitable and cost-effective way.

Data Collection

The next step is deploying our engineers to site to carry out the required service. This could mean moving our CPT Rigs to site to conduct an Intrusive Survey, deploying an engineer with a down-hole kit, or having one of our engineers conduct a Non-Intrusive Survey by either pushing, towing or flying the magnetometry sensors over the survey area.

Data Processing and Interpretation

Some of the data collected from our magnetometry kits is monitored in real time so that if an anomaly is identified, the engineer can abort the position for their safety, and the safety of everyone on site. This is particularly important when providing borehole support or conducting an Intrusive UXO Survey, as the last thing you ever want is our kit, a drill or piling rig striking an item of ordnance!

The data that is collected and sent back to our geophysics team undergoes rigorous processing to remove noise and improve data quality. The advanced software that our team uses will analyse the magnetic anomalies and compare them against a bank of known UXO signals. The software algorithms can also make estimations of the depths and mass for any suspect items that model like UXO, along with their location in coordinates accurate to 5 centimetres.

Verification and Excavation

The final step involves our engineering team investigating any anomalies that have been identified as potential UXO (if they are going to pose a hazard to ground intrusions). This process is called a Target Investigation and involves uploading the coordinates for the anomaly to a GPS system to pinpoint the identified target on site. Our team then use hand tools to unearth the targets, leaning on the resources of excavators for significantly deeper targets.

Advantages of Magnetometry in UXO Detection

Non-Invasive

One of the primary advantages of magnetometry is that thanks to our Non-Intrusive Survey capabilities we can detect potential UXO hidden below the surface without having to penetrate the ground. This methodology is ideal for areas that require minimal ground disturbance, for example on crop fields or sites that have high water tables.

Efficiency

Our magnetometry equipment enables efficient UXO detection, keeping project timelines moving along swiftly. For example, our UAV system can capture approximately 10 to 15 hectares of data per day depending on the terrain, compared with traditional systems which are only able to capture around 2 hectares per day.

Some of our equipment can also provide data in real time, ensuring maximum safety and efficiency on site.

High Sensitivity

Magnetometers are capable of detecting very small changes in the magnetic field, allowing them to identify even small UXO items buried beneath the surface. This high sensitivity ensures that even the most elusive ordnance can be detected and removed.

Challenges and Limitations

While magnetometry is a powerful tool for UXO detection, it does have some limitations. The presence of non-ferrous ordnance, such as those made from aluminium or plastic, cannot be detected using magnetometry alone.

Additionally, highly magnetic environments, such as those with a lot of ferrous debris, can create background noise that makes it difficult to identify specific UXO anomalies. To overcome these challenges, other UXO services might be recommended for certain construction and development sites.

UXO Detection at Brimstone UXO

Magnetometry stands at the forefront of UXO detection technology, offering a precise, efficient means of uncovering hidden dangers beneath the surface.

By understanding and leveraging the science of magnetometry, we at Brimstone UXO are committed to keeping projects safe from the dangers of UXO.

Keep up to date with Brimstone by following us on Facebook, Instagram, X (formerly known as Twitter), LinkedIn and YouTube.