Using satellites to monitor plastics in the world’s oceans

Overview

The use of plastic based materials offers large societal benefits. However, a by-product of the production of 250 million tonnes of plastic a year is the contamination of natural ecosystems by fugitive plastics [1]. The world’s oceans are one natural ecosystem where it is estimated that between 15 and 51 trillion pieces of plastic (est. 270,000 tonnes) have accumulated in the world’s oceans [2]. Due to ocean currents, this plastic tends to accumulate within five major ocean gyres that are referred to as “Garbage Patches”. Plastic here represents a hazard to animals through entanglement and ingestion, as well as a threat to the food chain from the accumulation of persistent organic pollutants.

The first step in tackling this problem is to quantify it; a particularly challenging task however given the large extent and remoteness of the Garbage Patches. Currently, quantification is limited to extrapolating information from a relatively small number of ocean trawls covering a limited area. There is therefore a pressing need for an approach that can offer reliable maps of plastic contamination at a global scale. This project aims to address this requirement by using satellite data.

It was recently shown for the first time an association between high densities of micro-plastic and regions of low backscatter in Synthetic Aperture Radar (SAR) satellite images. Dark areas can be due to substances that dampen the capillary waves on the sea surface [3]. We are hypothesising that this is related to the generation of surfactants from microbial degradation of plastics [4]. These fascinating observations suggest it might be feasible to use SAR data to quantitatively map the distribution and behaviour of micro-plastics in the ocean. Figure 1 presents one of the several images showing the dark features we hypothesise are indicators of micro-plastic presence.

In this project, we want to have a definitive proof that the dark features we observe in radar images are due to plastic. We will therefore perform ground and lab experiments able to assess the nature of the dark stripes.

In order to reject dark areas due to other meteorological events, we will investigate a combination and fusion of several satellite sensors including passive optical data. For instance, in the table of Figure 1 we also investigate chlorophyll-a and wind speed.

The successful candidate will undertake exciting multi-disciplinary work that involves:
1. Fieldwork and Laboratory experiments investigating the hypothesis that satellite data acquired by Synthetic Aperture Radar (SAR) can reliably detect plastics due to biofilm formation and a dampening of waves over the ocean surface.

2. Fusion of satellite sensors to try to quantify the amount of micro-plastic pollution.

In summary, this project aims to prove that we can quantify plastic accumulation in the world’s oceans with unprecedented resolution and accuracy. The obtained maps will help optimise future clean-up activities.

Click on an image to expand

Image Captions

Figure 1: Sentinel-1A SAR image showing presence of surfactants. Date of acquisition 14/06/14. The values of wind speed and chlorophyll-a are also indicated. ESA.

Methodology

Project objective: We want to use SAR combined with other satellite products to monitor and eventually quantify plastic pollution.

Deliverables: In this project, we will validate a series of methodologies that starting from images acquired from space will be able to provide estimates of micro-plastic pollution.

Novelty: Plastic pollution is a very challenging problem for the planet and cleaning missions may be foreseen in the future. Due to the size of the areas methodologies able to specify high concentration regions would save a significant amount of money. There is no known way to monitor micro-plastic concentration.

Data (satellite): Archive Copernicus data: this includes freely available Sentinel-1, Sentinel-2, ECMWF analysed data.

Methods: This project includes a) field/lab work and b) data analysis.

a) The field/lab work: The candidate will be working with field experiments in specified locations along the Scottish coastline. We will securely submerge microplastics in the water and observe the effect of this. The equipment are such that the probability of escaping plastics is negligible. Samples of the water will be taken periodically and we will analyse them with the Stirling Faculty of Natural Sciences lab facilities. Additionally, we will monitor the formation of biofilm by taking photographic evidences of their effect on capillary waves. We will also evaluate how different plastics types, concentration and location can affect the formation of biofilms. This will try to assess the detectability of different types of plastics in different locations. All the experiments will be considering control settings, where all the conditions are replicated except for the presence of plastics.

b) Processing of satellite data: The candidate will download freely available ESA Sentinel-1 SAR and Sentinel-2 optical images to observe and quantify the extent of plastic accumulation in oceans. The images will be processed using freely available ESA software and Python/Matlab.

Collaborations: this project has strong links with several partners in the UK. We will collaborate with experts in optical remote sensing of the ocean from the Plymouth Marine Laboratory. We will also have interactions with experts in microbial activities on plastic from the Open University. Finally, we will be in contact with end users interested in marine protection, including the Solway Firth Partnership. We will freely distribute our methodologies and results to partners and the general public, with the aim of producing some tangible change in practices. We will be involved in outreach events in the Solway Firth.

Project Timeline

Year 1

Preparing a literature review on microwave scattering from ocean and microbial production of surfactants. Field and lab work monitoring biofilm formation.

Year 2

Analysis of experimental data will be tackled and further experiments undertaken. Fusion of Sentinel-1 data with data from other sensors. Expected submission of journal paper on lab experiments.

Year 3

The student will use the data collected in the two previous experiments. Starting to write the thesis chapters. Expected submission of journal paper on fusion of sensor data.

Year 3.5

Complete thesis and submission.

Training
& Skills

This is a multi-disciplinary project including topics related to (a) Earth observation; (b) radar; (c) biology lab; (d) data handling and programing.
The successful candidate will have the opportunity to gain valuable skills in the context of: (a) carrying out laboratory experiments; (b) controlling electronic measurement devices; (c) analysing and processing satellite data using Python.
This work is linked to another project with ESA and the successful candidate could have the opportunity to visit a top-rank Chinese Universities in a training exchange and research collaboration.

References & further reading

[1] Andrady, A. L. Microplastics in the marine environment. Marine Pollution Bulletin 62, 1596-1605, doi:10.1016/j.marpolbul.2011.05.030 (2011).[2] van Sebille, E., Wilcox, C., Lebreton, L., Maximenko, N., Hardesty, B.D., van Franeker, J.A., Eriksen, M., Siegel, D., Galgani, F. and Law K.L. (2015) A global inventory of small floating plastic debris Environmental Research Letters, 10 (12).[3] Apel, C. R. J. a. J. R. in Synthetic Aperture Radar Marine User’s Manual Ch. 11, (NOAA, 2004).[4] Davaasuren, Narangerel; Marino, Armando; Ackermann, Nicolas; Alparone, Matteo; Nunziata, Ferdinando and Boardman, Carl (2018), Detecting microplastics pollution in world oceans using SAR remote sensingâ In: IGARSS 2018: IEEE International Geoscience and Remote Sensing Symposium, 22-27 Jul 2018, Valencia, Spain.[5] Five Gyres Institute http://5gyres.org/ (2015).

Further Information

Please contact Dr. Armando Marino for further information (Armando.marino@stir.ac.uk).

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