A compact, ruggedized fiber optic IR reflectance probe for remote, in-situ screening of underground waste sites has been developed. Using cabled chalcogenide optical fibers and a FTIR system, remote spectroscopy has been performed over distances of 20 meters. This paper discusses the design and performance of this system.
Infrared fiber optic reflectance spectroscopy is a powerful tool for identifying various organic compounds in soils. Using this technique a mixture of benzene and TCE on sand was measured; peaks due to both compounds are readily evident and correspond to the peaks in the pure liquid. At low concentrations of diesel fuel marine (DFM) on sand the band depths scale linearly with respect to DFM concentration. As the DFM concentration increases, the plot of DFM band depth versus concentration becomes nonlinear.
A novel fiber optic Raman probe for determination of organic vapors is described. The probe utilizes an absorbent resin, C-18, to concentrate the organic vapors in the optical path of the Raman probe. The probe exhibits a fully reversible response to organic vapors such as carbon tetrachloride or benzene.
The acquisition of fiber optic reflectance spectra of diesel fuel marine (DFM) dispersed on sea sand is described. Reflectance spectra are acquired by collection of the diffusely scattered light from a black body source imaged onto a specially designed sample cell. Samples of DFM were prepared by diluting a stock standard containing 10 wt% DFM on sea sand. Interactive band analysis is used to remove the background absorption due to residual water on the sand. Results indicate a linear relationship between the band depth at 3.68 microns and the concentration of DFM. Statistical analysis of ten replicate measurements of a 0.02 wt% DFM on sea sand gives the average band depth and 95% confidence interval of 0.02875 +/- 0.000654. An instrumental detection limit of 0.0033 percent reflectance is calculated from the standard deviation of the replicate measurements.
Currently there is a great deal of interest in the development and use of fiber optic chemical sensors for characterization of contaminated waste sites. Development of remote, in-situ sensors for rapid determination of the presence, and concentration of hazardous materials will significantly reduce site remediation costs. The state-of-the-art technology for assessing site contamination is the cone penetrometer system. This system consists of a 2-1/2 ton truck, a hydraulic ram, and a steel tube. The steel tube, which is generally 1-3/4 inches OD and 1 inch ID, has a sharp tip on one end. To begin site characterization the penetrometer tube is placed into the hydraulic ram then the tube is pushed into the ground. Sensors are mounted in the penetrometer tube to measure contaminants in the surrounding soil and ground water. This system has several distinct advantages over conventional drilling techniques. Additionally, site characterization can be performed much quicker than standard drilling techniques. Fiber optic chemical sensors are readily applicable towards use in cone penetrometer systems since they are small in size and can report real time, in-situ results. Some fiber optic chemical sensors have been deployed and tested in the cone penetrometer system.
Chlorinated hydrocarbons such as trichloroethylene and methylene chloride are common contaminants in soils at polluted sites. The chemical characterization of contaminated soils as a precursor to remediation is important. Raman spectroscopy is especially useful for the selective determination of a broad range of compounds. A fiber-optic Raman probe suitable for use in a soil environment has been constructed and tested. The intensity of the Raman signal of the chlorinated hydrocarbons trichloroethylene and methylene chloride has been measured in a variety of standard and nonstandard soil and sand samples. The effect of the soil parameters (opacity, particle size, etc.) on the intensity of the Raman signal has been investigated. The general implications for spectroscopic fiber optic chemical sensors used in a cone penetrometer system are discussed.
Surface mounted optical fiber strain sensors have been extensively used in smart structure sensing and actuator applications in the recent past. The performance of such sensors depends strongly on the conditions of bonding. Optimum static strain sensitivity of an extrinsic fiber optic interferometric strain gauge surface mounted on a cantilever beam was obtained by comparing several bonding techniques to each other, by comparing the outputs of the fiber sensors and resistance foil gauges, and by comparing the strain calculated from applied end displacements and elastic beam theory. The extrinsic fiber interferometer was formed between the ends of a single mode fiber (SMF) and a multimode fiber (MMF) inserted into a hollow core fiber (HCF) from opposite ends. Resistance foil and optical interferometric measurements were consistently lower than theoretical values. The closest agreement with theoretical values was realized by a configuration in which the SMF end was free to move within the HCF. For a sensor completely embedded in epoxy, optical strain measurements were 12.2% below theoretical values while the foil gauge readout was 18.1% lower.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.