Hyperspectral ultraviolet to shortwave infrared characteristics of marine-harvested, washed-ashore and virgin plastics
TL;DR: In this paper, the authors presented a dataset of Lambertian-equivalent spectralreflectance measurements from the ultraviolet (UV, 350 nm) to shortwave infrared (SWIR, 2500 nm) of synthetic hydrocarbons (plastics).
Abstract: . Combating the imminent environmental problems associated with plastic litter
requires a synergy of monitoring strategies, clean-up efforts, policymaking
and interdisciplinary scientific research. Lately, remote sensing
technologies have been evolving into a complementary monitoring strategy
that might have future applications in the operational detection and
tracking of plastic litter at repeated intervals covering wide geospatial
areas. We therefore present a dataset of Lambertian-equivalent spectral
reflectance measurements from the ultraviolet (UV, 350 nm) to shortwave
infrared (SWIR, 2500 nm) of synthetic hydrocarbons (plastics). Spectral
reflectance of wet and dry marine-harvested, washed-ashore, and virgin
plastics was measured outdoors with a hyperspectral spectroradiometer.
Samples were harvested from the major accumulation zones in the Atlantic and
Pacific oceans, suggesting a near representation of plastic litter in global
oceans. We determined a representative bulk average spectral reflectance for
the dry marine-harvested microplastics dataset available at https://doi.org/10.21232/jyxq-1m66 (Garaba and Dierssen,
2019c). Similar absorption features were identified in the dry samples of
washed-ashore plastics: dataset available at https://doi.org/10.21232/ex5j-0z25 (Garaba and Dierssen,
2019a). The virgin pellets samples consisted of 11 polymer types
typically found in floating aquatic plastic litter: dataset available at
https://doi.org/10.21232/C27H34 (Garaba and
Dierssen, 2017). Magnitude and shape features of the spectral reflectance
collected were also evaluated for two scenarios involving dry and wet
marine-harvested microplastics: dataset available at https://doi.org/10.21232/r7gg-yv83 (Garaba and Dierssen,
2019b). Reflectance of wet marine-harvested microplastics was noted to be
lower in magnitude but had similar spectral shape to that of dry
marine-harvested microplastics. Diagnostic absorption features common in the
marine-harvested microplastics and washed-ashore plastics were identified at
∼931 , 1215, 1417 and 1732 nm. In addition, we include metrics
for a subset of the marine-harvested microplastics related to particle
morphology, including sphericity and roundness. These datasets are also
expected to improve and expand the scientific evidence-based knowledge of
optical characteristics of common plastics found in aquatic litter.
Furthermore, these datasets have potential use in radiative transfer
simulations exploring the effects of plastics on ocean colour remote sensing
and developing algorithms applicable to remote detection of floating plastic
litter.
Citations
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TL;DR: The aquatic plastic litter detector and quantifier system (APLASTIC-Q) was developed and trained using very high geo-spatial resolution imagery (5 pixels/cm = 0.002 m/pixel) captured from aerial surveys in Cambodia as discussed by the authors.
Abstract: Large quantities of mismanaged plastic waste are polluting and threatening the health of the blue planet. Vast amounts of this plastic waste found in the oceans originates from land. It finds its way to the open ocean through rivers, waterways and estuarine systems. Here we present a novel machine learning algorithm based on convolutional neural networks (CNNs) that is capable of detecting and quantifying floating and washed ashore plastic litter. The aquatic plastic litter detector and quantifier system (APLASTIC–Q) was developed and trained using very high geo–spatial resolution imagery ~(5 pixels/cm = 0.002 m/pixel) captured from aerial surveys in Cambodia. APLASTIC–Q comprises two machine learning algorithms components (i) plastic litter detector (PLD–CNN) and (ii) plastic litter quantifier (PLQ–CNN). PLD–CNN managed to categorize targets as water, sand, vegetation and plastic litter with an 83 accuracy. It also provided a qualitative count of litter as low or high based on a thresholding approach. PLQ–CNN further distinguished and enumerated the litter items in each of the classes define as water bottles, Styrofoam, canisters, cartons, bowls, shoes, polystyrene packaging, cups, textile, carry bags small or large. The types and amounts of plastic litter provide benchmark information that is urgently needed for decision making by policymakers, citizens and stakeholders especially for developing plastic policies. Quasi–quantification was based on automated counts of items present in the imagery with caveats of underlying object in case of aggregated litter. Our scientific evidence–based algorithm based on machine learning complement net trawl surveys, field campaigns and clean–up activities for improved quantification of plastic litter. APLASTIC–Q will be an open–source smart algorithm that is easy to adapt for fast and automated detection as well as quantification of floating or washed ashore plastic litter from aerial, high–altitude pseudo satellites and space missions.
50 citations
TL;DR: The 2018 and 2019 Plastic Litter Projects are to date the only large-scale field experiments on the remote detection of floating marine litter in a near-real environment and can be used as a reference for more extensive validation/calibration campaigns.
Abstract: Remote sensing is a promising tool for the detection of floating marine plastics offering extensive area coverage and frequent observations While floating plastics are reported in high concentrations in many places around the globe, no referencing dataset exists either for understanding the spectral behavior of floating plastics in a real environment, or for calibrating remote sensing algorithms and validating their results To tackle this problem, we initiated the Plastic Litter Projects (PLPs), where large artificial plastic targets were constructed and deployed on the sea surface The first such experiment was realised in the summer of 2018 (PLP2018) with three large targets of 10 × 10 m Hereafter, we present the second Plastic Litter Project (PLP2019), where smaller 5 × 5 m targets were constructed to better simulate near-real conditions and examine the limitations of the detection with Sentinel-2 images The smaller targets and the multiple acquisition dates allowed for several observations, with the targets being connected in a modular way to create different configurations of various sizes, material composition and coverage A spectral signature for the PET (polyethylene terephthalate) targets was produced through modifying the US Geological Survey PET signature using an inverse spectral unmixing calculation, and the resulting signature was used to perform a matched filtering processing on the Sentinel-2 images The results provide evidence that under suitable conditions, pixels with a PET abundance fraction of at least as low as 25% can be successfully detected, while pinpointing several factors that significantly impact the detection capabilities To the best of our knowledge, the 2018 and 2019 Plastic Litter Projects are to date the only large-scale field experiments on the remote detection of floating marine litter in a near-real environment and can be used as a reference for more extensive validation/calibration campaigns
48 citations
TL;DR: In this paper, the authors used reflectance spectra of various types of floating matters to detect and discriminate marine microplastics from satellite observations in the visible and near infrared (NIR) spectral range.
39 citations
TL;DR: In this paper, the hyperspectral reflectances of virgin and naturally weathered polyethylene terephthalate (PET) submerged in water at varying suspended sediment concentrations and depth were studied.
Abstract: While at least 8 million tons of plastic litter are ending up in our oceans every year and research on marine litter detection is increasing, the spectral properties of wet as well as submerged plastics in natural marine environments are still largely unknown. Scientific evidence-based knowledge about these spectral characteristics has relevance especially to the research and development of future remote sensing technologies for plastic litter detection. In an effort to bridge this gap, we present one of the first studies about the hyperspectral reflectances of virgin and naturally weathered plastics submerged in water at varying suspended sediment concentrations and depth. We also conducted further analyses on the different polymer types such as Polyethylene terephthalate (PET), Polypropylene (PP), Polyester (PEST) and Low-density polyethylene (PE-LD) to better understand the effect of water absorption on their spectral reflectance. Results show the importance of using spectral wavebands in both the visible and shortwave infrared (SWIR) spectrum for litter detection, especially when plastics are wet or slightly submerged which is often the case in natural aquatic environments. Finally, we demonstrate in an example how to use the open access data set driven from this research as a reference for the development of marine litter detection algorithms.
32 citations
TL;DR: In this paper, a review of the challenges in microplastics analysis is presented, focusing on improving spatial resolution to detect smaller MP and development of robust models for data analysis, as well as reporting quality assurance and quality control measures.
Abstract: A central challenge in microplastics (MP, diameter 250 μm, with drastic improvements in analysis time as compared with the best available technology, such as Fourier transform infrared (FT-IR) and Raman spectroscopy. Primary challenges we identified through the review include improving spatial resolution to detect smaller MP and development of robust models for data analysis. Parameters and practices for reporting quality assurance and quality control measures are summarized and recommendations are made for future research. We conclude that HSI is a promising technology for MP analysis but requires adaptation for this new application.
24 citations
References
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TL;DR: This review of 68 studies compares the methodologies used for the identification and quantification of microplastics from the marine environment and suggests standardized sampling procedures which allow the spatiotemporal comparison ofmicroplastic abundance across marine environments.
Abstract: This review of 68 studies compares the methodologies used for the identification and quantification of microplastics from the marine environment. Three main sampling strategies were identified: selective, volume-reduced, and bulk sampling. Most sediment samples came from sandy beaches at the high tide line, and most seawater samples were taken at the sea surface using neuston nets. Four steps were distinguished during sample processing: density separation, filtration, sieving, and visual sorting of microplastics. Visual sorting was one of the most commonly used methods for the identification of microplastics (using type, shape, degradation stage, and color as criteria). Chemical and physical characteristics (e.g., specific density) were also used. The most reliable method to identify the chemical composition of microplastics is by infrared spectroscopy. Most studies reported that plastic fragments were polyethylene and polypropylene polymers. Units commonly used for abundance estimates are “items per m2” ...
3,119 citations
01 Oct 1977
TL;DR: This monograph presents a unified approach to the specification of reflectance in relation to the beam geometry of both the incident and the reflected flux in any reflectometer or in any application of measured reflectance data.
Abstract: Report presenting a unified approach to the specification of reflectance, in terms of both incident- and reflected- beam geometry. Nomenclature to facilitate this approach is proposed. Nomenclature for categorizing and specifying reflectance quantities for a variety of different beam configurations (both incident and reflected beams) is described, and all are defined and interrelated in terms of the bidirectional reflectance-distribution function. The conditions under which the formalism can be applied, including situations involving considerable sub-surface scattering, are carefully established. The entire treatment is limited to the domain of classical geometrical-optics radiometry and does not take into account interference and diffraction phenomena, such as are frequently encountered with highly coherent radiant flux.
1,757 citations
TL;DR: A new roundness scale is proposed defined by six roundness classes, defined by two sets of clay models prepared to characterize each roundness class and photographed to determine the roundness of a particle by comparison.
Abstract: A new roundness scale is proposed. This scale is defined by six roundness classes. Two sets of clay models were prepared to characterize each roundness class. One set shows a high sphericity, the other a low sphericity. Photographs of these models are used to determine the roundness of a particle by comparison.
1,406 citations
"Hyperspectral ultraviolet to shortw..." refers background in this paper
...I feel that the sphericity and roundness scale from Powers 1953 is outdated and inappropriate for use if the goal is radiative transfer simulation a simple aspect ratio would suffice....
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TL;DR: Results from 22 years of plankton tows in the North Atlantic showed the pattern of plastics accumulation was indeed as predicted by theories of ocean circulation, but, despite the steady increase in plastic production and disposal, the concentration of plastic debris had not increased and no trend in plastic concentration was observed in the region of highest accumulation.
Abstract: Plastic marine pollution is a major environmental concern, yet a quantitative description of the scope of this problem in the open ocean is lacking. Here, we present a time series of plastic content at the surface of the western North Atlantic Ocean and Caribbean Sea from 1986 to 2008. More than 60% of 6136 surface plankton net tows collected buoyant plastic pieces, typically millimeters in size. The highest concentration of plastic debris was observed in subtropical latitudes and associated with the observed large-scale convergence in surface currents predicted by Ekman dynamics. Despite a rapid increase in plastic production and disposal during this time period, no trend in plastic concentration was observed in the region of highest accumulation.
1,074 citations
TL;DR: A major ocean plastic accumulation zone formed in subtropical waters between California and Hawaii: The Great Pacific Garbage Patch is characterised and quantified, suggesting that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.
Abstract: Ocean plastic can persist in sea surface waters, eventually accumulating in remote areas of the world’s oceans. Here we characterise and quantify a major ocean plastic accumulation zone formed in subtropical waters between California and Hawaii: The Great Pacific Garbage Patch (GPGP). Our model, calibrated with data from multi-vessel and aircraft surveys, predicted at least 79 (45–129) thousand tonnes of ocean plastic are floating inside an area of 1.6 million km2; a figure four to sixteen times higher than previously reported. We explain this difference through the use of more robust methods to quantify larger debris. Over three-quarters of the GPGP mass was carried by debris larger than 5 cm and at least 46% was comprised of fishing nets. Microplastics accounted for 8% of the total mass but 94% of the estimated 1.8 (1.1–3.6) trillion pieces floating in the area. Plastic collected during our study has specific characteristics such as small surface-to-volume ratio, indicating that only certain types of debris have the capacity to persist and accumulate at the surface of the GPGP. Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.
959 citations