Seeing light over contaminated soil
Jul 9, 1998
The awareness of how much damage oil-spills, solvents and heavy metals can do in the environment has led to an explosive growth in new monitoring sensors. Now Rosario Sausa from the US Army Research Laboratory, Adelphi, Maryland, US, has developed a rugged reliable sensor (Patent 5759859) that can provide an almost instantaneous analysis of soil contamination.
The device works by utilizing a small hydraulic ram attached on the back of a truck. When the vehicle is parked in the sample area, the ram fires a metal rod 30 m into the soil. At the top of the rod, two pulse delay lasers - one operating in the infrared, the other near 452 nm in the visible region - pump light down a fibre optic cable to a transparent sapphire window at the base of the rod.
The pulse of infrared light heats the soil to over 400 oC in 1 microsecond, decomposing the soil and its contaminants to nitrogen oxide (NO) compounds. The visible wavelength beam then ionizes these NO molecules. Two electrodes placed near the window collect the charged particles. This 'ion' current is then converted into an amplified voltage signal and sent to an analysis unit on board the truck. Repeating the procedure at a number of depths and locations in the area can allow scientists to create a three-dimensional map of the contaminants in the region.