FEATURE HYPERSPECTRAL IMAGING
Plastic not fantastic
Greg Blackman looks at how SWIR spectral imaging can help reduce plastic pollution, both through environmental surveys and by improving sorting in recycling plants
O
ur reliance on plastic is putting enormous strain on our oceans and rivers. And it’s incredibly hard to get rid of once it’s there – 12 million
tonnes of plastic a year enters the marine environment, according to a Eunomia report in 2016.
On Henderson Island, an uninhabited
atoll in the South Pacific, plastic has been found from Russia, the USA, Europe, South America, Japan and China. Despite no people, plastic was washed up on the shores of this 14-square-mile island at a rate of 3,500 pieces a day, reported National Geographic in 2017, carried by the South Pacific gyre ocean current. What’s more worrying is that Henderson is a Unesco World Heritage site due to its biological diversity. Unesco describe it as ‘one
26 Electro Optics March 2021
of the world’s best remaining examples of an elevated coral atoll ecosystem’. Cleaning the oceans remains a difficult
proposition, but one that groups are working on, notably the Ocean Cleanup project, which caught its first plastic in the Great Pacific Garbage Patch in 2019. More than a ‘patch’, it is the largest accumulation of ocean plastic in the world. It is between Hawaii and California and covers 1.6 million square kilometres, roughly three times the size of France, where it’s estimated that 1.8 trillion pieces of plastic, weighing about 80,000 tonnes are churning about.
The Ocean Cleanup team has built a floating
structure that creates an artificial shoreline. By applying drag so that the parachute-shaped structure moves slower than the current,
plastic washes up and accumulates over time. The floating system can catch pieces of rubbish millimetres in size up to large items like abandoned fishing nets. The team’s models have suggested that a full-scale rollout could catch half of the plastic in the patch in five years. Hyperspectral imaging, especially
working in the shortwave infrared (SWIR), has an important role to play in reducing plastic pollution, thanks to its ability to distinguish between different types of plastic. The technology is being investigated as a potential way to identify plastics in natural ecosystems, while also showing promise for use in recycling plants to sort plastics. A lot of emphasis is put on preventing plastics from entering rivers and oceans in the first place, through better product and packaging design, avoiding single-use plastics, and improved waste handling and recycling, which is where vision technology comes in. Researchers at Texas A&M University- Corpus Christi are working on image processing algorithms to differentiate between different plastics based on SWIR hyperspectral data. The idea is to eventually use this technology to search for plastic pollution in the environment. Professor Ruby Mehrubeoglu, who is leading the work, said that, when combined with an effective classification algorithm, SWIR hyperspectral imaging has ‘the potential to assist with not only detection and identification of plastics, but also management of plastic pollution in the long run’.
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