REMOTE SENSING


Te hyperspectral view from space


Abigail Williams speaks to scientists tracking marine plastic using satellite spectral imagery


H


yperspectral imaging and remote sensing are emerging as key tools for tracking plastic pollution in


the world’s oceans. Tere’s a lot of scientific research using satellite images, and the European Space Agency is supporting a number of remote sensing projects in this area. Projects like Trace, which uses


hyperspectral data from the Italian Space Agency’s Prisma satellite (see the glossary for a list of satellites mentioned in this piece), along with other satellite imagery, to develop a system to track large marine litter and accumulation zones in oceans. Mathias Bochow, environmental scientist


at the Helmholtz Centre, Potsdam, part of the GFZ German Research Centre for Geosciences, is working on the project. He said: ‘While high-resolution, multispectral data enables tracking of floating objects, only hyperspectral data enables material identification. We need to capture a hyperspectral image of a location that allows us to assume where floating litter will be over the next few days to be able to say it is really marine litter and not drifting algae or wood.’ In addition to the Prisma images – and


EnMap images once launched – data from multispectral satellites in the PlanetScope constellation were used, alongside the Tiresias oceanographic forecasting model developed by CNR-ISMAR. Bochow noted the ability to track floating


objects has only become possible following the launch of the PlanetScope satellite fleet, which captures images from locations around the Earth every day. Although the fleet is typically only used to obtain images over land and coastal zones, images were recorded over the Adriatic Sea for this project.


Mathias Bochow, GFZ Helmholtz Centre, Potsdam, is working on the Trace project to track marine plastic ‘High frequent imaging over time enables


tracking of floating objects when linked with an oceanographic forecasting system. We are about to find out how well this works over the next month,’ said Bochow. Spectral capabilities in the shortwave


infrared (SWIR), between around 1,000nm and 2,500nm, are important for identifying plastics, because of the material’s spectral fingerprint at these wavelengths. According to András Jung, co-founder of spectral camera firm Cubert, hyperspectral imaging can be used to sort plastic at a macroscopic level, such as everyday waste products from household or industry. He said there are many successful applications between 400nm and 1,000nm for this. But hyperspectral imaging can also be used to detect microplastics in water, and in this case the SWIR region is more useful. Professor Jonathan Chan, ETRO


guest professor at the Vrije Universiteit Brussel, noted that the ideal sensor to detect marine plastic should possess more spectral measurement


16 IMAGING AND MACHINE VISION EUROPE APRIL/MAY 2022


capabilities at SWIR wavelengths. Chan is working on the Muss2 project,


which is using spectral and spatial enhancement methods to generate simulated Earth orbit hyperspectral shortwave infrared images and data from the Copernicus Sentinel 2 satellite using spectral response function modelling. Hyperspectral images taken from Earth


orbit are not always available and their coverage is not as large as conventional missions, such as Landsat and Sentinel. To overcome these limitations, Chan said the Muss2 team will apply a sparse theory- based method to enhance multispectral images from the Sentinel 2 satellite. Te expected results are what he described as synthetic Sentinel 2 hyperspectral images at a spatial resolution of 10m, with the same coverage as Sentinel 2 multispectral images. ‘So far, we have been able to generate


such images based on Hyperion and Prisma spectral configurations, [and] quantitative assessments are promising,’ he said. ‘In addition, we apply a deep learning-based


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Mathias Bochow/GFZ


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