REMOTE SENSING


method for the spatial enhancement of Prisma images to assist in the detection of smaller objects.’ Chan added: ‘All the data inputs for the


project are from open sources, including Sentinel 2, Hyperion and Prisma. Te launch of Prisma in 2019 was a major milestone, and soon EnMap will be launched. Tese are full stretch hyperspectral images at 400- 2,500nm with hundreds of spectral bands and represent the most powerful Earth orbit data source for environmental monitoring. Te potential is not yet fully understood nor exploited, and scientific communities are just beginning to understand all the pre-processing protocols and data quality issues.’


Signed, sealed, delivered Another interesting initiative is the Spots project, which aims to study the hyperspectral signature of floating plastic debris under less-than-ideal circumstances. As Robin de Vries, geospatial analyst at Te Ocean Cleanup non-profit organisation, explained, hyperspectral satellite data has the potential to be a key component in the remote sensing of floating plastic debris. He said: ‘Te hyperspectral signature is


affected when plastic is submerged, or when it becomes covered by biological growth over time, known as biofouling. Te Spots project is important because many studies have only investigated the detection of floating plastic under ideal conditions.’ Te key objectives of the Spots project


are to gather a spectral library of different plastics under varying water depth and biofouling scenarios, and to explore predictive models to estimate depth of water, material type and degree of biofouling from the hyperspectral signature. According to de Vries, the project team


‘Te potential is not yet fully exploited; scientific communities are just beginning to understand all the pre-processing protocols’


has already collected most of the laboratory and field data and, although it is too early to share any definite results, he said the scientists are already finding that material thickness and water depth have profound and sometimes unexpected effects on the hyperspectral signature of plastics. Troughout the project the Spots team


will make use of a range of hyperspectral imaging technology, including a Bayspec OCI-F imager, a Spectral Evolution SR- 3501 spectrophotometer, and a Specim IQ snapshot hyperspectral camera. ‘Tis equipment is only suitable for


use in controlled environments,’ de Vries explained. ‘Tis means that we collect data of plastic in a controlled environment, to learn how we can best extrapolate it to applied remote sensing in the future.’ He added: ‘At this stage, it is challenging


to apply multispectral and hyperspectral sensors in the field for applied remote sensing for dispersed marine litter. Te main reasons for this are the relatively high cost of the equipment and the limited spatial resolution, as well as the long sensor integration times, compared with a dynamic environment such as flowing rivers or ocean waves.’


Polarised potential Elsewhere, the Ocean Plastics Polarisation Properties (OP3


) project is focused on


obtaining fully characterised polarisation signatures of plastic marine litter in relation to other natural seawater constituents. Tis is through a combination of laboratory experimentation, in situ measurements and existing polarisation data from satellite missions, such as Parasol. As Tristan Harmel, research scientist at


Géosciences Environnement Toulouse, explained, remote sensing of plastic marine litter can be challenging because of the very high water absorption in the NIR-SWIR range, and the signal being masked during atmospheric correction. Harmel said that complementary


optical information is needed to detect plastics in the oceans. Te polarisation state of light leaving water has been shown to be a significant tool to disentangle complex marine signals to retrieve water constituents. To sense the two important elements


of polarisation and directionality, Harmel explained that specific setups are needed in the laboratory, as well as in the field and from satellite platforms. For the latter, he said the historical French mission, Parasol, which contained the Polder instrument, was of particular interest because Polder sensors provided polarisation at three spectral bands (blue, red and near infrared) for up to 16 different viewing directions. Moving forward, he said the next


generation of satellite polarimeters will also provide a much more refined dataset encompassing the visible, NIR and SWIR bands. Tese include the 3MI instrument, to be launched on the Eumetsat Metop- SG series of satellites, which will provide multispectral (410-2,130nm), multi- polarised (-60°, 0°, and +60°) and multi- angular images of outgoing radiance at the top of the atmosphere. In addition,


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