A Scaled, Machine Learning Approach to Cleaning up Floating Plastics in
the Ocean
Abstract
It took less than two decades for plastics to become notable marine
contaminants following their initial commercial introductions. In the
ensuing five decades, global plastics production has increased 500%
each year. Currently, 300 million metric tons of plastic are produced
every year much of this ends up in the ocean. In the mid-1970s it was
thought that most of this plastic derived from discarded trash by
ocean-going vessels. Now, we know that plastic debris in the oceans is
exported by nearly all the major rivers of the world, as well as from
shing, aquaculture, petrochemical, and shipping industrial sources.
These plastics are long-chain polymers that are extremely durable in the
environment, which is in part, why they become troublesome pollution.
One practical difficulty is that in addition to the massive geographic
extent of the plastic debris, the distribution is patchy in 4 dimensions
(i.e., length, width, depth, time). Our approach takes advantage of the
unique spectral signatures of floating plastic that can be identified in
freely available Sentinel-2 imagery from the European Space Agency
(ESA). Recent analytical developments identified a floating plastic
index (FPI; Biermann et al. 2020) that takes a ratio of red, red edge,
NIR, and SWIR bands (4, 6, 8, and 11 respectively) to discriminate
between floating plastic and other floating materials such as foam, wood
and vegetation. Here we present a scaled approach to identify patches of
floating plastic and generate coordinates to guide cleanup efforts. The
initial area of interest is 100 km on a side and is passed through
hierarchical loops that 1.) separate land from water; 2.) interrogate
the image files for pixels with reflectance values consistent with FPI;
and, 3.) generate pixel centroid coordinates for image pixels that
contain suspected floating plastic pollution. To overcome the coarse
spatial (20m, bands 6 and 11) and temporal (ca. 5 days) resolution, and
dynamic nearshore environment, remotely piloted aerial systems (RPAS)
navigate to pixel centroids to confirm plastic accumulations. Once
identified and located, updated coordinates guide navigation via
autopilot in autonomous sweeper drone vessels. These sweeper drones are
equipped with stereo bow-mounted hyperspectral cameras that scan the
proximal waters to identify precise locations of floating plastic, plot
a navigation solution, and engage the drone’s sweeper apparatus to
collect the plastic. The approach integrates, distributed processing of
satellite imagery in the cloud, RPAS verification of plastic locations,
communication with navigation software and hardware of cleanup vessels
to plot navigation solutions at the 10m scale. Finally, onboard
hyperspectral cameras collect and process stereo imagery to identify
precise targets which are layered on the navigation software and
hardware system to direct cleanup actions. The approach is comprised of
five hierarchically integrated modules that include: Coarse Location Map