Beached Plastic Debris Index; a modern index for detecting plastics on beaches.

Plastic pollution on shorelines poses a significant threat to coastal ecosystems, underscoring the urgent need for scalable detection methods to facilitate debris removal. In this study, the Beached Plastic Debris Index (BPDI) was developed to detect plastic accumulation on beaches using shortwave infrared spectral features. To validate the BPDI, plastic targets with varying sub-pixel covers were placed on a sand spit and captured using WorldView-3 satellite imagery. The performance of the BPDI was analysed in comparison with the Normalized Difference Plastic Index (NDPI), the Plastic Index (PI), and two hydrocarbon indices (HI, HC). The BPDI successfully detected the plastic targets from sand, water, and vegetation, outperforming the other indices and identifying pixels with <30 % plastic cover. The robustness of the BPDI suggests its potential as an effective tool for mapping plastic debris accumulations along coastlines.