Operational use of multispectral images for macro-litter mapping and categorization by Unmanned Aerial Vehicle.

The use of Unmanned Aerial Systems (UAS, aka drones) has shown to be feasible to perform marine litter surveys. We operationally tested the use of multispectral images (5 bands) to classify litter type and material on a beach-dune system. For litter categorization by their multispectral characteristics, the Spectral Angle Mapping (SAM) technique was adopted. The SAM-based categorization of litter agreed with the visual classification, thus multispectral images can be used to fasten and/or making more robust the manual RGB image screening. Fully automated detection returned an F-score of 0.64, and a reasonable categorization of litter. Overall, the image-based litter density maps were in line with the manual detection. Assessments were promising given the complexity of the study area, where different dunes plants and partially-buried items challenged the UAS-based litter detection. The method can be easily implemented for both floating and beached litter, to advance litter survey in the environment. • Multispectral images from drone to categorize stranded litter materials and type • Sample Angle Mapper classifier adopted to process multispectral orthophoto • 42 litter items collected among the litter bulk and used as spectral references • Adequate litter materials and types categorization, despite the complex background • Multispectral images from drone can improve and advance litter survey in the environment. [ABSTRACT FROM AUTHOR]