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Mapping ocean litter from space with existing satellites

Aerial drone image of a litter in the Bay of Biscay, Spain.  Swath width: 1-2 meters.  (Credit: ESA)
Aerial drone image of a litter in the Bay of Biscay, Spain. Swath width: 1-2 meters. (Credit: ESA)

Recently, ESA published the results of a proof-of-concept study on monitoring marine litter using existing satellites, with promising results for the Mediterranean study area. The study used six years of historical data from the Sentinel-2 satellite multispectral imaging cameras, with 300,000 images at a resolution of 10 meters. The emphasis was on litter. These are common collections of litter such as plastic, wood and other types of marine debris that float on the surface and form clearly visible lines that can be meters wide and many times as long.

These have been processed as explained in the open access document Nature communication by (Andrés Cózar) and colleagues. Because marine litter is usually overwhelmingly plastic, this facilitates detection, as it can generally be assumed that all litter visible from space is mainly plastic litter. This was combined with the spectral profile of common plastics so that other types of floating materials (algae, driftwood, sea foam, etc.) could be filtered out, leaving only the litter.

This revealed many of these short-lived swaths of litter, confirming the presence of ships in the area. Some swaths were many kilometers long, with an average of about 1 km.

Although it is only a PoC, it still shows that monitoring such plastic waste from space is very possible, even without special satellites. With tons more plastic entering the oceans every day, this gives us the means to at least map the scale of the problem. Even though solving it and the associated microplastics problem is still a distant dream.

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