Abstract

The feasibility of using fiber-optic based laser-induced fluorescence (LIF) for real-time in situ subsurface screening of petroleum hydrocarbons was first demonstrated through a joint (Army, Navy, Air Force) development program. The Site Characterization and Analysis Penetrometer System (SCAPS) program integrated a fiberoptic based LIF sensor with an instrumented probe that could be pushed into the ground to depths of 50 m with a hydraulic ram in a cone penetrometer vehicle. The first cond penetrometer deployed LIF sensor used an optical fiber up to 100 m in length to deliver light from a pulsed nitrogen laser emitting at 337 nanometers to induce fluorescence in aromatic hydrocarbons through a sapphire window in the penetrometer probe. Fluorescence form polycyclic aromatic hydrocarbons is returned to the surface over a second optical fiber where it is spectrally quantified using a photodiode array detector. Validation studies where fluorescence data is compared directly against laboratory measurements on discrete soil samples show that the LIF sensor has a high utility as a real-time, semi-quantitative field screening method for petroleum hydrocarbons.

© 1996 Optical Society of America