Scattering characteristics of metal and plastic mines at 16 GHz

Abstract

Single-polarity, synthetic aperture radar (SAR) data collected in spotlight mode is examined as part of an effort to identify surface land mines in high-frequency radar imagery. A measurements program was recently conducted using a Ku-band (16 GHz) radar. In this experiment, metal and plastic mines were placed on smooth dirt lanes and in tall and short grass areas adjacent to these lanes. The collected data set consisted of magnitude-only data for several different passes over a common target area that included various reference reflectors as well as the landmines. The metal and plastic mines on the dirt lanes were clearly visible in the processed radar imager, while the mines in the grass areas were not observable - even after applying multi-look averaging. (Multi-look averaging exploits the circular symmetry of the mines to enhance the contrast between the mines and the background clutter). To investigate these effects, we used rigorous moment method-based electromagnetic solvers to compute the backscatter from the metal and plastic mines in a variety of backgrounds. The model results were shown to be consistent with the measurement data for metal mines on the dirt lanes. The plastic mines were not consistent with the data, however. We believe that the difference is due to uncertainty in the mine dielectric constant. The model results also showed that a significant focusing effect (or “glory wave”) could be seen in the plastic mines at low depression angles. Finally, the model demonstrated the highly absorptive nature of the grass, as shown by the significantly reduced radar cross section of mines placed in a three-layer grass model.