Unexploded Ordnance Detection
For the detection of unexploded ordnance or metal-cased mines in large depths, Vallon offers two technologies:
1. The active Pulse Induction method
The active pulse induction system offers great advantages in terms of UXO detection in mineralised soils in which magnetometers are giving too many false alarms. Likewise, for quick search of sub munitions and shells, the large search head, combined with a special UXO signal processing in the metal detector, offers high efficiency.
The large search head of a Vallon metal detector continuously emits electromagnetic pulses. Between each magnetic pulse is a short pause. During these pauses the electromagnetic reaction from metal objects, influenced by the search head, is detected by the detector.
The reaction time is depending on the size of the metallic objects and their distance to the search head. The receiver of the detectors processes this response and converts it to an alarm signal.
Search head sizes of 30 cm and 60 cm diameter are used, depending on surface conditions.
2. The Gradient Magnetometer Method
The magnetic field of the earth is homogeneous with regards to the field strength and the direction of the field strength. If a ferromagnetic object is brought into this homogeneous field, the own field of the object is superposing the local magnetic field of the earth, hence creating a distortion.
With increasing distance from the object the field distortion is decreasing.
The extent of the distortion depends on several factors. The most important ones are the size of the object to be detected and its permeability. The larger the object to be detected is the larger will be the detection distance.
If the buried object is magnetized, i.e. it has an own magnetic field, the field lines are reacting according to the polarity of the object. In general, the total disturbance of magnetized objects is larger than the disturbance of objects having no own field. But very rarely the total disturbance might even be smaller depending on the object orientation towards the terrestrial magnetic field.
UXO detectors are differential magnetometers, i.e. two sensors are arranged in geometrically true alignment at a certain distance and are connected in a way that they measure the value zero in a homogeneous field. Each sensor passing a ferrous object is differently affected. The indication of the gauge is in nT with ± 20 degrees and deflects to plus or minus depending on the orientation of the object in the ground.
This method can be used for detection on the surface, in boreholes and under water. For more than 10 years now, computerised detection with automatic calculation of object location, size and depth with VALLON EVA 2000® software has been available.
More detailed information can be given upon request.