Improved analytical signal (IAS): a new phase-based-filter for detection of unexploded ordnance. (English)
Unexploded ordnance, such as bombs, mines, and projectiles, represent a serious worldwide problem, especially in places where armed conflicts has occurred. Most UXOs in Europe came from the First and Second World Wars. The wars in Syria, Libya, Iraq, and Yemen represent examples of more recent military conflicts where dangerous ordnance, such as grenades, mortars, landmines, projectiles, and bombs, remain unexploded and buried beneath under the earth’s surface, at risk of detonation. This study aimed to develop a more precise, rapid and cost-effective approach to locating unexploded ordnance in near real-time using geophysical methods. It adopted an edge-detection method significantly increasing accuracy and inherent noise reduction in the process of interpreting magnetic anomalies, as compared to the most common magnetic methods that ‘spread’ the ordinance footprint relative to its actual size. The study team developed and tested a new phase-based filter:improved analytical signal (IAS) using the first-order derivatives of the analytical signal of the magnetic field through a normalisation process. The main advantage of the IAS filter was that it was less influenced by the background signal than other filters and provided a clear image of the subsurface magnetic structures with good equalisation of anomalies from shallow- and deep-seated sources bodies. The magnetic surveying was carried out close to a former army shooting range in Rohoznik, Slovakia where several UXO objects are buried. The IAS filter was tested on noise-free and noisy synthetic magnetic data, as well as on magnetic data collected in the field. The efficiency of the new filter was validated by comparison to other known edge detectors using these synthetic and real magnetic data. The IAS edge detector showed better results in detecting buried UXOs for both weak and strong anomalies and also for shallow and deep targets. It also demonstrated an ability to discriminate UXOs from other metallic bodies.