Prospects of remote sensing for monitoring plastic litter in freshwater environments: A systematic review

Abstract

Mismanaged plastics have been persistent in the natural environment for extended periods of time, threatening the health of aquatic and terrestrial ecosystems. Milestones have been achieved in exploratory efforts to use remote sensing for monitoring plastics in marine environments, but little has been done in freshwater systems. We present a systematic assessment of the various remote sensing platforms, sensor characteristics, and detection algorithms for plastic litter monitoring in freshwater environments. The literature search yielded twenty-eight studies published between January 2010 and March 2024. These studies were largely conducted on rivers in Asia, Europe, and North America, showing a lack of research in Africa, Australia, and South America. This underscores the need for region-specific research to support monitoring of plastic litter in freshwater environments. Drones and multispectral satellites were observed as the most frequently used imaging platforms, accounting for 48.3 % and 17.2 %, respectively of the platforms used in the studies. These helped to demonstrate the capabilities of data captured mainly in visible and near-infrared regions. Variations in Ground Sampling Distance (GSD) were also observed, indicating a lack of standardized protocols for drone surveys. Although lower flight altitudes are essential for acquiring high spatial resolution data (lower GSD), this review shows that reduced flying height does not always result in higher spatial resolution, demonstrating the influence of other parameters like camera sensor specifications. Similarly, although conducted in freshwater environments, these studies relied on plastic spectral characteristics derived from marine environment experiments, which may be insufficient for complex freshwater bodies.

Keywords

• Plastic litter
• Remote sensing
• Freshwater environments