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Open AccessArticle

Development of a Cost-Effective Optical Sensor for Continuous Monitoring of Turbidity and Suspended Particulate Matter in Marine Environment

1
MEMS-UMinho, University of Minho, Campus de Azurém, 4800-471 Guimarães, Portugal
2
LARSyS, University of Algarve Campus de Gambelas, 8005-139 Faro, Portugal
3
Institute of Earth Sciences, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
4
Centre of Molecular and Environmental Biology (CBMA), University of Minho, 4710-057 Braga, Portugal
*
Authors to whom correspondence should be addressed.
Sensors 2019, 19(20), 4439; https://doi.org/10.3390/s19204439
Received: 16 September 2019 / Revised: 28 September 2019 / Accepted: 9 October 2019 / Published: 14 October 2019
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
A cost-effective optical sensor for continuous in-situ monitoring of turbidity and suspended particulate matter concentration (SPM), with a production cost in raw materials less than 20 €, is presented for marine or fluvial applications. The sensor uses an infrared LED and three photodetectors with three different positions related to the light source—135º, 90º and 0º—resulting in three different types of light detection: backscattering, nephelometry and transmitted light, respectively. This design allows monitoring in any type of environment, offering a wide dynamic range and accuracy for low and high turbidity or SPM values. An ultraviolet emitter–receiver pair is also used to differentiate organic and inorganic matter through the differences in absorption at different wavelengths. The optical transducers are built in a watertight structure with a radial configuration where a printed circuit board with the electronic signal coupling is assembled. An in-lab calibration of the sensor was made to establish a relation between suspended particulate matter (SPM) or the turbidity (NTU) to the photodetectors’ electrical output value in Volts. Two different sizes of seashore sand were used (180 µm and 350 µm) to evaluate the particle size susceptibility. The sensor was tested in a fluvial environment to evaluate SPM change during sediment transport caused by rain, and a real test of 22 days continuous in-situ monitoring was realized to evaluate its performance in a tidal area. The monitoring results were analysed, showing the SPM change during tidal cycles as well as the influence of the external light and biofouling problems. View Full-Text
Keywords: in-situ measurement; oceanography; suspended particulate matter; turbidity optical sensor in-situ measurement; oceanography; suspended particulate matter; turbidity optical sensor
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Matos, T.; Faria, C.L.; Martins, M.S.; Henriques, R.; Gomes, P.A.; Goncalves, L.M. Development of a Cost-Effective Optical Sensor for Continuous Monitoring of Turbidity and Suspended Particulate Matter in Marine Environment. Sensors 2019, 19, 4439.

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