Detecting plastic pollution in the ocean with advanced remote sensing technologies

In a large-scale hydrodynamic testing facility at Deltares (the Delta Basin), different microwave and optical methods were investigated to determine the most effective ways to spot plastic waste.

Collecting data with satellites

Satellites allow us to cover large areas and collect data on a regular basis. This makes it possible to monitor changes in plastic pollution over long periods of time and identify hotspots of plastic waste.

Satellites can carry both microwave and optical sensors to detect plastic. Microwave sensors are particularly useful because they can see through clouds and rain, which often hinders optical sensors. This allows satellites to collect data continuously and in different weather conditions. With microwave sensors, we collect data on the roughness of the water surface. With optical sensors we look at the colour and infrared properties of plastic items. In that way we get a picture of what is floating in the waste. In short, both techniques have different properties that can help better map the plastic problem at sea.

First step taken towards application

The study with the test facility showed that microwave sensors, especially those with X- and Ku-bands, were very effective in detecting plastic items when there was at least one item per square metre. In addition, optical sensors, which use light to identify objects, could distinguish plastics based on their unique optical propperties.

The study's findings show which techniques are interesting to test further in open water conditions, such as in rivers and seas. Key research questions for follow-up and possible application concern the detectability of plastics when overgrown with pollution, and to what extent capillary waves can be used to better locate plastics. Once we can better track plastic hotspots via space, it will make for more effective clean-up operations and will help policymakers worldwide to protect surface waters.

This research is of outermost importance for the European Space Agency (ESA) to understand and develop space-based technologies for global monitoring of the ocean to study the evolution of the plastic litter problem and to trigger interventions in severely affected areas.

Erio Gandini, Antenna Engineer ESA

The scientific article is open access available at Nature

Video about the research in the Delta Basin