Mapping Windrows as Proxies for Marine Litter Monitoring from Space (WASP)

WASP (Windrows AS Proxies) is a data processor, developed in the frame of the European Space Agency (ESA) OSIP Campaign, exploiting Copernicus Sentinel-2 L1C images to detect and catalogue the presence of filaments of floating marine debris with high probability of containing man-made litter. WASP takes advantage of the prototype EO data processor developed in the frame of ESA project  “Earth Observation (EO) Track for Marine Litter (ML) in the Mediterranean Sea” that successfully proved for first time that Copernicus Sentinel-2 data can detect the presence of marine litter accumulations as proxies of plastic litter content.

WASP puts significant effort in masking unneeded data that has been source of false-positive detections, including sun glint and clouds. Also, a new spectral analysis technique has been employed to identify the most promising Copernicus Sentinel-2 bands to be used in the detection of such filaments, which has also led to the construction of a novel spectral index WASP Spectral Index (WSI). This index enables the detection of filaments of floating debris.

The images processed using WSI are transformed into binary masks to be analysed by a deterministic object classifier, which looks at the geometry and shapes of the detections to identify ML windrows within them and separate them from background noise and/or false positives. This enables automatic processing and classification of the images, which makes possible to generate regional and/or local databases of remote-sensed floating debris, which can be exploited by means of geostatistics to support research and monitoring of marine litter in the environment.

These implementations are also supported with the introduction of advanced super-resolution techniques that are downscaling the spatial resolution of the bands to 10m, well beyond the simple interpolation, yielding better quality on the results.

In a preliminary assessment, the implemented proposed algorithm has proven to be successful in identifying windrows even when those are too thin to be visible in True Colour images by the naked eye. Nevertheless, some drawbacks/limitations have been found, principally associated to residual limitations when removing bad data, and with the special case of the problematic wave glint, well known in the Sentinel-2 data but of difficult solution.

Once the entire Sentinel-2 archive over the Mediterranean Sea is processed and following an in-depth analysis, a database of the identified proxies, including spatial and temporal patterns will be created over this initial region. The final EO product will be a map of on sub-mesoscale marine debris concentrations in the Mediterranean Sea based on Copernicus Sentinel-2. The product will consist on a census of these structures for each processed tile for the Mediterranean Sea, with potential for global scalability. Scientific research, cleaning activities and policy making on marine litter are only a few of the activities that could benefit from such a product.

This activity collaborates on the “Remote Sensing of Marine Litter and Debris” IOCCG taskforce.