To predict whether detection potential is above or below detection benchmarks for different equipment (including dogs and rats), we must understand the relationship between flux rate, target scent at surface level, and the effects of weather and soil properties on migration of vapour through the soil. Defining the limits of detection will assist in understanding the optimal deployment of animal detector systems, and productivity and safety should also be improved.
In order to fully evaluate field performance results, simulation modelling should be performed to estimate the landmine chemical vapour emanations and surface soil residues that might be expected in various daily and seasonal time periods. The simulation model requires appropriate input data including mine source emission rates, soil-water-air partitioning, and the full compliment of weather data. Model improvements may depend on geographical location of the mine dog performance tests (for inclusion of plants), whether surface rainfall runoff is important and whether vapour plume definition is desired (surface soil-atmosphere interface).
Since 1997, work supported by the United States Defence Advanced Research Projects Agency, Electronic Dog's Nose Project, investigated many aspects of environmental processes, including laboratory and field results of chemical transport in soils from buried landmines. As part of this effort, the computer code T2TNT (Webb et al., 1999) was developed to simulate the chemical movement from landmines including the impact of environmental conditions such as wind, rain, and temperature. The effect of weather cycles on the surface flux of various chemicals has been demonstrated by Webb and Phelan (2000), which indicated orders of magnitude variation in short time periods due to wetting and drying cycles. The GICHD has funded application of T2TNT to landmine scenarios in Afghanistan and Bosnia. The effect of weather cycles on the chemical signatures for these two locales has been documented.
The GICHD has expanded the project to involve additional T2TNT simulations. There are two separate tasks. The first task is analysis of environmental factors for three different locales. In addition, Sandia used the mine flux data for three different mine types being obtained at Sandia in order to assess the difference in chemical signature between different mine types. The second task is further evaluation of the predictive capability of T2TNT.
The T2TNT model is being developed for use in support of humanitarian demining worldwide. However, users of this tool require special training to understand data input requirements and interpretation of results. While T2TNT is not currently available for widespread use, it is intended for a broader users group when desired. This would provide dual benefit in increasing the analysis capability worldwide for chemical sensing for buried landmines, and to provide feedback for improvements needed in this simulation tool.
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Guy Rhodes
