Adaptive Ground Penetrating Radar Systems to Visualize Antipersonnel Plastic Landmines Based on Local Texture in Scattering / Reflection Data in Space and Frequency Domains

Ground penetrating radars (GPRs) are widely used for buried object search, ruin investigation, groundwater assessment, and other various applications (Sato & Takeshita, 2000) (Moriyama et al., 1997). They are also expected to find nonmetallic landmines (Bourgeois & Smith, 1998) (Montoya & Smith, 1999) (Peters Jr. & Daniels, 1994) (Sato et al., 2004) (Sato, 2005) (Sato et al., 2006). Figure 1 shows the size and the structure of a plastic antipersonnel landmine. A near future target is to find or visualize antipersonnel landmines with a high distinction rate between landmines and other objects. The conventional metal detectors, based on electromagnetic induction, use so low frequency that the electromagnetic field penetrates through the soil very deep, and the false negative probability is very small. However, because of its long wavelength, the resolution is limited, and they can tell just whether inductive material exists or not. They cannot distinguish landmines from other metal fragments. GPRs employ much higher frequency. Then the resulting higher resolution will be helpful to discriminate landmines. Currently, there are two methods to remove the plastic landmines. One is a metal detector, and the other is a rotary cutter. The former detects a blasting cap made of metal in the landmine. Because the cap is very small, we must set the sensitivity at a high level. Then, the positive fault rate is as high as about 99.9% (specificity=0.1%), resulting in a lot of time to remove the landmines. The latter, rotary cutter, looks like a bulldozer, bores the ground and tries to clear the landmines by exploding them. The problems in this method are necessity of additional removal by human because of impossibility of perfect clearance, necessity of sufficient areas for the approach of the rotary cutter, and land pollution by the exploded powder. Accordingly, though these methods have certain merits, they have also demerits. Therefore, new landmine detection systems based on GPRs attract attention and are studied by a dozen of researcher groups/laboratories presently to solve the problem. Most of the proposed methods employ high-frequency and wide-band electromagnetic wave to visualize a plastic landmine itself instead of the metallic blasting cap. There are two types among the