Remote detection of nitroaromatic explosives in soil using distributed sensor particles

Abstract

Environmental fate and transport studies of explosives in soil indicate that 2,4,6-trinitrotoluene (TNT) and similar products such as dinitrotoluene (DNT) are major contributors to the trace chemical signature emanating from buried landmines. Chemical analysis methods are under development that have great potential to detect mines, or to rapidly classify electromagnetically detected anomalies as mines vs. "mine-like objects". However, these chemical methods are currently confined to point sensors. In contrast, we have developed a method that can remotely determine the presence of nitroaromatic explosives in surface soil. This method utilizes a novel distributed granular sensor approach in combination with uv-visible fluorescence LIDAR (Light Detection and Ranging) technology. We have produced prototype sensor particles that combine sample preconcentration, explosives sensing, signal amplification, and optical signal output functions. These particles can be sprayed onto soil areas that are suspected of explosives contamination. By design, the fluorescence emission spectrum of the distributed particles is strongly affected by absorption of nitroaromatic explosives from the surrounding environment. Using ~1mg/cm 2 coverage of the sensor particles on natural soil, we have observed significant spectral changes due to TNT concentrations in the ppm range (µg TNT/g soil) on 2-inch diameter targets at a standoff distance of 0.5 km. These field measurements have also been used to validate calculations of fluorescent signal/noise for the granular sensor particles as a function of several variables, including particle and receiver characteristics, standoff range, pump laser characteristics, and particle coverage. Some implications of these measurements and calculations for field deployment of the sensor particles are discussed.