5:15 PM - 7:15 PM
[STT42-P04] High sensitivity simultaneous measurement of sea surface vector current and temperature based on polarization interference of Panda fiber
Keywords:sea surface vector flow, seawater temperature, Panda polarization-maintaining fiber, hollow cylindrical cantilever beam, optical vernier effect
Ocean currents represent one of the most common forms of seawater movement. Accurate and direct measurement of sea surface flow fields is essential for monitoring global climate change, studying ocean dynamics, and investigating air-sea interactions along with their physical and biochemical processes. Seawater temperature, as a fundamental hydrological parameter, is an indispensable physical variable in various marine science studies, and it also plays a critical role in driving horizontal and vertical seawater movements, thermohaline circulation, and ocean currents. Therefore, long-term monitoring of ocean currents and seawater temperature holds significant importance for fisheries, shipping, pollution discharge, marine economy, and military operations. Due to the problems such as the high cost, substantial maintenance requirements, and risks of water and electrical leakage associated with traditional electrical current meters and thermometers for simultaneous measurement of currents and temperature, as well as the absence of research reports on fiber optic sensing for multi-parameter measurement of seawater vector flow and temperature, and facing the urgent requirement of the integrated sensor of ocean current and temperature in the current Marine scientific research, it is urgent to develop a novel optical fiber sensing method with high sensitivity, simple structure and stable performance for the simultaneous measurement of seawater vector current and temperature.
A fiber optic sensing method for simultaneous measurement of seawater flow velocity, direction, and temperature is proposed by coupling three reflective Panda fiber optic polarization interferometers with a hollow cylindrical cantilever beam structure. The flow velocity measurement principle is based on the relationship between seawater velocity and the bending stress of the cantilever beam, as well as the strain sensing mechanism of the Panda fiber optic polarization interferometer. Two fiber optic sensing units are orthogonally coupled to the outer surface of the cantilever beam to measure two components of seawater flow velocity, and their results are used for vector synthesis of flow velocity and direction. The third sensing unit is wrapped around the underwater target to measure seawater temperature, and it forms an optical vernier effect with the fiber optic sensing units used for flow velocity component measurement, effectively amplifying the sensitivity of flow velocity and temperature. A wavelength division multiplexing (WDM) system was employed to redistribute the light source, and a flow direction measurement method based on a rotatable base was designed. Building on this, a laboratory system for measuring flow velocity, direction, and temperature was established, and experiments on three-parameter sensing and measurement were conducted. The experimental results indicate that the maximum flow velocity sensitivity of the fiber optic sensing unit used for flow velocity component measurement is expressed as Sv=152.6v(nm/(m/s)), with a relative error of 1.4% compared to the theoretical sensitivity. For the fiber optic sensing unit used for flow velocity component measurement combined with the optical vernier effect, the maximum flow velocity sensitivity is expressed as Sv=-425.8v(nm/(m/s)), with a relative error of 2.8%. Additionally, the maximum temperature sensitivity of the fiber optic sensing unit used for temperature measurement combined with the optical vernier effect is expressed as ST=-7.6nm/℃, with a relative error of -5.23% compared to the theoretical sensitivity.Finally, 24 sets of three-parameter measurement experiments were conducted, covering a temperature range of 17.6℃–28.1℃, a flow velocity range of 0.064m/s–0.466m/s, and a flow direction range of 0°–360°. The flow velocity measurement results of the fiber optic sensor were compared with ADV monitoring results, the temperature measurement results were compared with CTD monitoring results, and the flow direction measurement results were compared with the rotation angle of the rotatable base. The experimental results show that the average relative error of temperature measurement is -0.6%, and the average relative errors of flow velocity magnitude and direction measurement are -1.5% and -1.1%, respectively. These results further validate the measurement capabilities of the proposed fiber optic sensor in the fields of seawater flow velocity, direction, and temperature, demonstrating its potential for significant application in future field measurements of ocean currents and temperature.
A fiber optic sensing method for simultaneous measurement of seawater flow velocity, direction, and temperature is proposed by coupling three reflective Panda fiber optic polarization interferometers with a hollow cylindrical cantilever beam structure. The flow velocity measurement principle is based on the relationship between seawater velocity and the bending stress of the cantilever beam, as well as the strain sensing mechanism of the Panda fiber optic polarization interferometer. Two fiber optic sensing units are orthogonally coupled to the outer surface of the cantilever beam to measure two components of seawater flow velocity, and their results are used for vector synthesis of flow velocity and direction. The third sensing unit is wrapped around the underwater target to measure seawater temperature, and it forms an optical vernier effect with the fiber optic sensing units used for flow velocity component measurement, effectively amplifying the sensitivity of flow velocity and temperature. A wavelength division multiplexing (WDM) system was employed to redistribute the light source, and a flow direction measurement method based on a rotatable base was designed. Building on this, a laboratory system for measuring flow velocity, direction, and temperature was established, and experiments on three-parameter sensing and measurement were conducted. The experimental results indicate that the maximum flow velocity sensitivity of the fiber optic sensing unit used for flow velocity component measurement is expressed as Sv=152.6v(nm/(m/s)), with a relative error of 1.4% compared to the theoretical sensitivity. For the fiber optic sensing unit used for flow velocity component measurement combined with the optical vernier effect, the maximum flow velocity sensitivity is expressed as Sv=-425.8v(nm/(m/s)), with a relative error of 2.8%. Additionally, the maximum temperature sensitivity of the fiber optic sensing unit used for temperature measurement combined with the optical vernier effect is expressed as ST=-7.6nm/℃, with a relative error of -5.23% compared to the theoretical sensitivity.Finally, 24 sets of three-parameter measurement experiments were conducted, covering a temperature range of 17.6℃–28.1℃, a flow velocity range of 0.064m/s–0.466m/s, and a flow direction range of 0°–360°. The flow velocity measurement results of the fiber optic sensor were compared with ADV monitoring results, the temperature measurement results were compared with CTD monitoring results, and the flow direction measurement results were compared with the rotation angle of the rotatable base. The experimental results show that the average relative error of temperature measurement is -0.6%, and the average relative errors of flow velocity magnitude and direction measurement are -1.5% and -1.1%, respectively. These results further validate the measurement capabilities of the proposed fiber optic sensor in the fields of seawater flow velocity, direction, and temperature, demonstrating its potential for significant application in future field measurements of ocean currents and temperature.