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Classification of suspended particles in seawater using an in situ polarized light scattering prototype
Summary
This study developed and field-tested an underwater sensor that uses polarized light scattering to distinguish between microplastics, sediment particles, and phytoplankton in seawater in real time. Lab tests showed classification accuracy above 85%, and the device was successfully deployed in a Chinese coastal bay across two seasons. Such in-situ monitoring tools could greatly improve our ability to track microplastic concentrations in the ocean without the labor-intensive sample collection and lab analysis currently required.
Abstract Classification of suspended particles characterizes the composition of seawater, which helps the interpretation of remote sensing data and promotes the researches of the matter exchanges in ocean processes. In this article, an in situ prototype based on polarized light scattering is introduced, and its ability to classify the suspended particles is demonstrated. The experimental results show that the prototype can classify the sediments, microplastics, and phytoplankton in seawater with an accuracy larger than 85%, and further calculate their relative proportion in water. In the summer and winter of 2020, the prototype was deployed three times in Daya Bay and lasted for dozens of hours each time, along with the additional commercial sensors, that is, Environment X Observation (EXO) and Acoustic Doppler Current Profiler (ADCP). The chlorophyll content measured by EXO and the acoustic backscatter intensity measured by ADCP are respectively related to the number of algal cells and sediments in the water, which helps to interpret the data of the prototype. The results of field data show that the prototype can effectively classify phytoplankton and sediment particles in seawater and monitor their temporal variations. Besides, the retrieved information of the suspended particles is consistent with the analysis from the flow dynamics and season variations in Daya Bay. These results indicate the ability of this prototype to classify the suspended particles in seawater, which promises its potential contribution to particulate oceanography in the future.