Optical-fiber-based groundwater sensor for monitoring landfill sites

摘要

Abstract: This paper describes an optical fiber based sensor for detecting groundwater and for monitoring the concentration of particulate material which may be entrained in that water. The sensing system uses white light from a multi-wavelength spectral source which is transmitted through a 200 micrometer diameter multimode fiber to a sensing head. The infra-red portion of the light acts as a reference while the visible part is transmitted through a sampling area and is reflected back in to a receiving fiber. The reference and modulated spectra are detected by a dual epitaxial diode. Electronic processing results in compression of the information from an intensity versus wavelength format to a single number called dominant wavelength. This number is different for air and water, and for water with and without particulates. The discrimination between air and water is possible because of differences in the absorption spectra and refractive indices, and between water with and without particulates through Mie scattering. !4