Advances and the future of remote sensing of floating litter 

Earth Observation (EO) technologies can provide large scale systematic monitoring capabilities of all floating marine matter composed mostly of plastic based items. The main monitoring capabilities that have been demonstrated using EO include detection, identification, quantification and tracking of floating marine matter. The detection of floating matter from EO technologies is achieved by understanding and leveraging  unique signal characteristics which can be observed remotely, and for which litter is different from the background or from other optically active materials. A broad range of different EO sensor technologies have been investigated with respect to floating matter including LiDAR, MiDAR, RADAR and multi-angle polarimetry. The vast majority of the work on detection of floating matter and marine plastics however is being performed using optical imaging, with passive sensors. The distinctive feature here is the reflectance of floating matter and plastics. Most types of floating matter have much higher reflectance than the reflectance of water, especially in the NIR and SWIR spectral range.  This offers a strong basis for straightforward detection of floating matter vs. water, although it does not necessarily indicate that different types (i.e., natural or anthropogenic) of floating matter can be distinguished. Here we will present a critical review of the capabilities and limitations of optical satellites to monitor floating matter and marine plastics. We further asses the requirements for a new satellite mission for the monitoring of marine plastic litter.