Particle Simulation of Floating Marine Debris with Statistical Debris Estimation in Coastal Areas of Japan

Marine pollution in coastal areas is a serious threat to the local ecosystem and human activities.

Marine debris is mainly advected by ocean currents and localized winds, making it difficult to forecast the accumulation of debris in advance. Since the long-term exposure to the natural environment results in the degradation of the debris into environmentally harmful components, the marine debris should be removed as soon as possible.

This paper presents validation methods of the particle simulation in the coastal ocean with a rough estimation of debris accumulation using satellite images. Our process divides into two steps; 1. A rough estimate of debris accumulation on a large scale, and 2. Particle simulation of floating marine debris.

We proposed an image processing pipeline for debris density estimation [1]. This model is established from the obtained satellite images coinciding with the ground truth data, which are clean-up records. This processing pipeline is based on a semantic segmentation model and estimates the presence of the debris by computing Shannon's entropy and basing the debris level on this value.

We selected contaminated regions based on the results of this estimation method. Then, we performed particle simulations near the selected areas. This simulation is based on the Lagrangian framework to look at debris transportation along the fluid motion. We used the local reanalysis ocean currents product provided by Japan Meteorological Agency (JMA) and defined field sets that are similar to the actual local situations based on our ground truth data. We, then, compared the floating particle densities with the estimated debris density inferred by satellite observations.

We confirmed that our statistical approach coincides with the trends by the physical modeling, which enables us to predict the rough discharged areas of marine debris.

[1] K. Sasaki, T. Sekine, L. -J. Burtz and W. Emery, "Coastal Marine Debris Detection and Density Mapping with Very High Resolution Satellite Imagery," in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2022, doi: 10.1109/JSTARS.2022.3193993.