Monitoring marine plastic pollution using radar: from source to sea

Abstract

Marine plastic pollution poses a significant threat to ocean ecosystems worldwide, necessitating effective monitoring and management strategies. The use of remote sensing plays a vital role in providing large-scale, frequently-timed data for monitoring this issue. A multi-modal system has been deemed the most appropriate for tackling the monitoring of marine debris and pollution. Synthetic Aperture Radar (SAR) can provide a wealth of data by taking advantage of the systems ability to acquire in near all-weather conditions, night and daytime. However, research in radar and SARs capability in monitoring marine plastic pollution is lacking. This thesis aims to provide an insight into these capabilities. This is through a series of experiments and investigations into the responses of SAR / Radar to marine plastic litter. Chapter two presents a real-world scenario of plastic accumulation within a river environment. The use of SAR imagery is employed to identify plastic accumulations in two separate study locations. A hypothesis of SAR backscattering interactions with plastic debris is presented. A suite of detectors are subsequently implemented to understand how to best utilise the SAR signal for marine debris detection in these test cases, with the best detector used to create heatmaps of debris accumulation within our test sites. The following chapter provides the results of two rigorous measurement campaigns, where C- and X-band radar data are exploited in a lab experiment. Backscatter and statistical analysis are undertaken across multiple tests involving differing plastic items, concentrations, and wave conditions. From this, interactions between plastic size, shape, and wave conditions are explored. A new interaction for backscatter interactions with plastic debris is also presented. The final data chapter investigates the potential use of a proxy for plastic pollution. Two measurement campaigns are conducted which utilise plastisphere based surfactants, and their interactions for wave dampening, to understand if this is detectable in radar data. For the first time, detailed analysis of backscatter values from differing plastic items and concentrations are presented, as well as the utilisation of real-world test cases. The results obtained in this thesis provide novel insights and additions to recent literature that contributes to our understanding of the capabilities of radar for marine plastic pollution monitoring, as well as new information that can be used in the planning for future missions and studies on the remote sensing of marine plastic pollution.