Abstract
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.
Highlights
In both oceanography and limnology, turbidity is of great importance in the study of the development conditions of the euphotic zone, where the passage of sunlight is crucial for the development of marine flora [1], study of the sediments transport phenomena [2,3] and study of water quality [4], those for human consumption
In-lab calibrations to suspend particulate matter, organic material and formazin turbidity standards were established to prepare the device for in-situ deployments, as well as for readings are strongly dependent on calibration methodology
In-lab calibrations to suspend particulate matter, organic material (phytoplankton) and formazin turbidity standards were established to prepare the device for in-situ deployments, as well as for readings are strongly dependent on calibration methodology
Summary
In both oceanography and limnology, turbidity is of great importance in the study of the development conditions of the euphotic zone, where the passage of sunlight is crucial for the development of marine flora [1], study of the sediments transport phenomena [2,3] and study of water quality [4], those for human consumption. Turbidity is a physical property of fluids that translates into reduced optical transparency due to the presence of suspended and dissolved materials that block the passage of light [5]. These materials can be of organic or inorganic origin, varying in colour, matter and size, ranging from macroscopic to colloidal particles [6]. The current optical turbidity sensors make use the lightvalue. Particulate attenuatesediments light through scattering correlation withhave the turbidity value.contribution. Particulate materials attenuate light substances through scattering but can a significant to total primarily absorption. Dissolved scatter but can have a significant contribution to total absorption
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