Fiber optic sensing system for in-situ simultaneous monitoring of water stage, quality, and temperature

Abstract

To accurately track the water stage changes and environmental influences on water quality and have sufficient follow-ups to prevent potential flood and environmental hazards, an in-situ continuous monitoring system for water stage and quality is helpful. Traditional in-situ water-stage monitoring system has relative low accuracy and require separate sensors for water quality and temperature which complex the evaluation. Advanced optical fiber sensors, with unique features of real-time and multiparameter sensing capacity, could provide potential simultaneous evaluation of flooding, water-quality deterioration, and science-based decision support. In this study, an in-situ monitoring system for water stage, overall water quality, and temperature is developed using long-period fiber grating (LPFG) sensors. When part of the LPFG sensor is submerged in water, the resonant wavelength of each cladding mode of the LPFG sensor varies linearly with the submerged length (refer to water stage) and temperature, and nonlinearly with refractive index changes (referred to the water quality). Two resonant wavelengths were used to relate the water stage and overall water quality to the change in resonant wavelengths of the LPFG sensor. Sharing the same fiber line, one sequential glass packaged LPFG was used to monitor the temperature changes at the same location. The algorithm for simultaneous determination of the water stage, overall water quality, and temperature was analytically formulated and experimentally validated. Benefit from the multi-parameter sensing using one single fiber line, the developed optical sensing network can potentially provide a low-cost, real-time, and high resolution solution for the in-situ water quality monitoring.