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In situ spectral analysis of sea ice contaminated with multiple substances in Liaodong Bay, Bohai Sea
Summary
Researchers measured the optical reflectance of sea ice in China's Bohai Sea contaminated with five different substances and found that microplastic fragments uniquely increased visible-band reflectance above that of clean ice, while coal and oil produced distinct spectral signatures that could enable remote sensing identification of different contaminant types.
The Bohai Sea is under considerable environmental stress due to the significant discharge of inland contaminants. Understanding the optical properties of contaminated sea ice in this region is essential for improving large-scale remote sensing of sea ice contamination. This study investigated the in situ spectral properties of sea ice contaminated with five contaminants, including sediment, motor oil, pulverized coal, charcoal powder, and secondary microplastic fragments, along the eastern coast of Liaodong Bay in the Bohai Sea. The results revealed that most contaminated sea ice exhibited lower reflectance than clean sea ice in the ultraviolet, visible, and near-infrared bands. Specifically, sea ice contaminated with pulverized coal (0.28) and charcoal powder (0.23) showed the lowest reflectance in the visible band. However, sea ice contaminated with secondary microplastic fragments (0.88) had a higher reflectance in the visible band compared to clean sea ice (0.75). Motor oil-contaminated sea ice displayed distinct absorption features between 500 and 550 nm, with the 560 nm wavelength offering a potential band for distinguishing this contaminant from others. In the shortwave infrared region (beyond 1400 nm), all contaminants exhibited higher reflectance than clean sea ice. Sediment-covered sea ice was most recognizable by its high reflectance difference at 1725 nm. Correlation analyses showed strong negative correlations between contaminant mass and reflectance in sea ice contaminated with pulverized coal and charcoal powder across the 350-1350 nm range, while beyond 1430 nm, sediment, secondary microplastic fragments, and charcoal powder exhibited strong positive correlations with contaminant mass.