Abstract
Abstract—Plastics have permeated almost every aspect of modern day life with its wide applicability. The tragic consequence is
millions of pieces of plastic polluting and harming sea life every day. The road towards a clean sea contains several legs and requires
mapping of the ocean water column to determine critical areas. Determining technologies and methods for the detection of
microplastics underwater are hence a necessity. Raman spectroscopy is such a technology, in principle able to extract the chemical
structure of the object to be viewed by collecting spectral signatures at the point illuminated. This creates the foundation for the
research presented in this paper, aiming to cover whether it is possible to classify specific types of microplastics underwater by
identifying their respective spectral signatures. Raman spectroscopy has been carried out on three different cases of samples. The first
case involves known plastic, ordered from CARAT AS, with the purpose of creating the foundation of a partial least squares
discriminant analysis (PLS-DA) model. The second case holds the same base but includes drops of water on top of the original
sample. This case provided data for testing the prediction of the PLS-DA model. The third case includes raw plastic pieces, collected
from the sea outside Svolvær, Lofoten. The measurements of these samples create the grounds for the last test-set. The results
suggest that the method can classify microplastic correctly, both in water and sea-influenced pieces. However, the specific spectra
cannot vary too much as a result of industrial and environmental changes altering the condition of the plastic, and thereby the
spectrum. This leaves the mapping and classification method best suited for plastics that recently entered the ocean.
millions of pieces of plastic polluting and harming sea life every day. The road towards a clean sea contains several legs and requires
mapping of the ocean water column to determine critical areas. Determining technologies and methods for the detection of
microplastics underwater are hence a necessity. Raman spectroscopy is such a technology, in principle able to extract the chemical
structure of the object to be viewed by collecting spectral signatures at the point illuminated. This creates the foundation for the
research presented in this paper, aiming to cover whether it is possible to classify specific types of microplastics underwater by
identifying their respective spectral signatures. Raman spectroscopy has been carried out on three different cases of samples. The first
case involves known plastic, ordered from CARAT AS, with the purpose of creating the foundation of a partial least squares
discriminant analysis (PLS-DA) model. The second case holds the same base but includes drops of water on top of the original
sample. This case provided data for testing the prediction of the PLS-DA model. The third case includes raw plastic pieces, collected
from the sea outside Svolvær, Lofoten. The measurements of these samples create the grounds for the last test-set. The results
suggest that the method can classify microplastic correctly, both in water and sea-influenced pieces. However, the specific spectra
cannot vary too much as a result of industrial and environmental changes altering the condition of the plastic, and thereby the
spectrum. This leaves the mapping and classification method best suited for plastics that recently entered the ocean.
