Multifunctional RF- and Radar-Systems (MFR)

Mines and explosive devices claim numerous lives. Radar can be used to detect them underground, but it often also mistakenly identifies harmless objects as mines. A radar system developed by Fraunhofer FHR aims to reduce these false-positive rates in the future.

Thousands of people lose their lives each year due to landmines – many of them civilians. In addition to military-laid landmines, improvised explosive devices (IEDs), such as canisters filled with explosive fertilizers, also claim victims. Ground-penetrating radar can assist in locating these deadly, buried weapons so they can be neutralized. The radar devices emit electromagnetic waves that are reflected back by the ground and buried objects to varying degrees. The problem is that the data often does not reveal whether an object is a landmine or something harmless, like screws or similar objects – the false-positive rate is particularly high in wet and heterogeneous soils. This results in longer clearance times and higher costs: Digging up an empty drink can wastes time and money, and in conflict zones, it also increases the risk of being shot at.

Improved Mine Detection Through Full Polarimetry and Multistatic Radar

Researchers at Fraunhofer FHR are working to enhance the quality of the data obtained and significantly reduce the false-positive rate. This is being achieved with the development of a full polarimetric and multistatic radar sensor. In conventional radar, linearly polarized radar waves are used – waves that oscillate in only one plane. When these waves encounter an object, such as a mine buried in the ground, the plane of oscillation changes depending on the geometry of the object. A full polarimetric radar can operate with two polarizations in both the transmission and reception paths. This allows for the determination of changes in polarization and the extraction of geometric features like edges and corners. Consequently, it may be possible to better differentiate between dangerous and non-dangerous objects in the future. The resolution of the full polarimetric radar is currently four to five centimeters.

Multistatic radar, on the other hand, uses a multitude of antennas: Whereas conventional radar systems use one antenna to emit a signal and another to receive the reflected signal, multistatic radar employs multiple receiving antennas. The advantage is that each antenna »views« the surroundings or ground from a slightly different angle, providing more data and thereby increasing the probability of detecting mines.

First Measurement Campaign Successful

At Fraunhofer FHR, a small antenna array consisting of six antennas, each with two polarization planes, was initially constructed. Even with this compact setup, 144 receiving channels were already achieved. In a measurement campaign, the radar system underwent its first test. In a hall, researchers set up a »sandbox« in the fall of 2023, where they buried a dummy of a person mine – 12 centimeters in diameter and without any metal content – as well as screws and cartridge casings. The mine was clearly visible in the radar images. As for the screws, they are barely distinguishable from the landmine with conventional radar, given that the resolution is four to five centimeters, which is larger than the size of a screw. However, polarimetry made a significant difference: Different geometries of objects alter the polarization plane in distinct ways, making a clear distinction between the angular screws and the flat mines observable – an additional piece of information that can be utilized in explosive detection. Another measurement campaign is planned for summer 2024 at a German Armed Forces test site.Mines and explosive devices claim numerous lives. Radar can be used to detect them underground, but it often also mistakenly identifies harmless objects as mines. A radar system developed by Fraunhofer FHR aims to reduce these false-positive rates in the future.

Thousands of people lose their lives each year due to landmines – many of them civilians. In addition to military-laid landmines, improvised explosive devices (IEDs), such as canisters filled with explosive fertilizers, also claim victims. Ground-penetrating radar can assist in locating these deadly, buried weapons so they can be neutralized. The radar devices emit electromagnetic waves that are reflected back by the ground and buried objects to varying degrees. The problem is that the data often does not reveal whether an object is a landmine or something harmless, like screws or similar objects – the false-positive rate is particularly high in wet and heterogeneous soils. This results in longer clearance times and higher costs: Digging up an empty drink can wastes time and money, and in conflict zones, it also increases the risk of being shot at.

Improved Mine Detection Through Full Polarimetry and Multistatic Radar

Researchers at Fraunhofer FHR are working to enhance the quality of the data obtained and significantly reduce the false-positive rate. This is being achieved with the development of a full polarimetric and multistatic radar sensor. In conventional radar, linearly polarized radar waves are used – waves that oscillate in only one plane. When these waves encounter an object, such as a mine buried in the ground, the plane of oscillation changes depending on the geometry of the object. A full polarimetric radar can operate with two polarizations in both the transmission and reception paths. This allows for the determination of changes in polarization and the extraction of geometric features like edges and corners. Consequently, it may be possible to better differentiate between dangerous and non-dangerous objects in the future. The resolution of the full polarimetric radar is currently four to five centimeters.

Multistatic radar, on the other hand, uses a multitude of antennas: Whereas conventional radar systems use one antenna to emit a signal and another to receive the reflected signal, multistatic radar employs multiple receiving antennas. The advantage is that each antenna »views« the surroundings or ground from a slightly different angle, providing more data and thereby increasing the probability of detecting mines.

First Measurement Campaign Successful

At Fraunhofer FHR, a small antenna array consisting of six antennas, each with two polarization planes, was initially constructed. Even with this compact setup, 144 receiving channels were already achieved. In a measurement campaign, the radar system underwent its first test. In a hall, researchers set up a »sandbox« in the fall of 2023, where they buried a dummy of a person mine – 12 centimeters in diameter and without any metal content – as well as screws and cartridge casings. The mine was clearly visible in the radar images. As for the screws, they are barely distinguishable from the landmine with conventional radar, given that the resolution is four to five centimeters, which is larger than the size of a screw. However, polarimetry made a significant difference: Different geometries of objects alter the polarization plane in distinct ways, making a clear distinction between the angular screws and the flat mines observable – an additional piece of information that can be utilized in explosive detection. Another measurement campaign is planned for summer 2024 at a German Armed Forces test site.