Remote Sensing Monitoring of Marine Plastic Litter: From macroplastics to microplastics

Marine plastic litter presents a pervasive and escalating threat to global marine ecosystems, which urgently requires effective monitoring techniques. Remote sensing offers significant potential for large-scale and repetitive monitoring. While remote sensing of macroplastics has demonstrated feasibility through direct detection, the monitoring of microplastics is constrained by the spatial resolution and radiometric sensitivity of remote sensors. Since direct detection of microplastics remains highly challenging, current approaches primarily rely on indirect environmental proxies. However, these proxy-based methods face key challenges arising from signal-background confusion, uncertain proxy origins, inconsistent proxy-plastic correspondence, and spatiotemporal scale inconsistencies. Consequently, we propose that future research should pivot toward proxy-background discrimination, proxy source discrimination, physics-informed proxy modeling, and spatiotemporal matching. The ultimate goal is to build a more robust and reliable monitoring framework, effectively bridging the gap 'from macroplastics to microplastics.'