GPR combined with a positioning system to detect anti-personnel landmines

Landmines and explosive remnants of war (ERW) are a serious problem in many countries around the world. In 2012, there were, on average, ten casualties per day globally [1]. Anti-Personnel (AP) landmines have been developed to have only a small amount of metal content, thus making them harder to find with metal detectors. Often there is less metal in a landmine than in “clutter” metallic objects, which are also found during the de-mining process. One reason landmine removal is a time-consuming task using the conventional metal detector is that it is not possible to classify the objects very accurately; consequently all positive signals must be investigated with equal caution. However, the dielectric material (e.g. main charge and plastic case) surrounding the metal detonator components generally occurs in landmines, and less so in clutter. Metal objects detected by a dual sensor without an associated detection of plastic objects can be ignored unless they are metal AP mines. One way to detect the plastic is to add a Ground Penetrating Radar system (GPR) to the conventional metal detector. Developments over the last decade combining GPR with traditional inductive metal detection have demonstrated the value of this approach [2]. GPR data is generally analysed by collating a series of reflection responses (A-Scans), collected over an evenly spaced series of positions in a single direction. This data set is termed a B-Scan. On conventional geotechnical GPR systems, a position encoder is attached to one of the wheels, in order to capture the data at regular intervals. Metal-detector type AP landmine detection systems are handheld devices without wheels, so some other way of detecting position needs to be found other than the operator's location. This paper describes an investigation into a positioning system for a handheld scanner. It describes how inertial measurements combined with a camera can determine the antenna position during the sensor sweep and how this information can be used to create the conventional B-Scan data sets. The paper compares the antenna-to-ground separation measurement extracted from both time and frequency domain GPR measurement systems to that given by an ultrasound distance sensor.