Satellite remote sensing of marine litter floating in open ocean and coastal waters

Abstract

The remote sensing of marine litter is becoming increasingly important. Disasters such as floods cause large amounts of natural and man-made waste to enter coastal waters. Since such large-scale floating litter is an obstacle to safe operation of ships and recreation activities, it is necessary to issue an alert and remove it as quickly as possible. In addition, since man-made plastic litter adversely affects not only the aesthetics but also the marine ecosystem, interest in reducing plastic waste is higher than ever. Some of the plastic waste entered into the ocean and moves along the ocean current over a long period of time, threatening the life of marine animals. Numerous clean-up operations are being undertaken. Mapping areas of plastic litter accumulation in the ocean is certainly useful for efficient operations. However, it is still challenging to reliably detect marine litter from space. One of the key technique to do is to detect changes in reflectance to identify small patches floating on the ocean surface. The spatial anomaly in reflectance was calculated by subtracting the spatially varying reflectance of the surrounding background water from the satellite-measured reflectance, and it was used to detect reflectance changes due to presence of drifting litter patches. By applying this technique to high-resolution images of Worldview-3, we investigated the possibility of detecting plastic litter in Great Pacific Garbage Patch. Specifically, anomaly spectra were evaluated to detect plastic litter using the Ocean cleanup System 001 Wilson as a known target. While floating litter in the open ocean is found isolated, it is often observed accumulated along the water fronts. We applied the same technique to different-scale events in coastal waters using images from various satellite sensors including PlanetScope, MSI and GOCI. In addition to the change of reflectance due to the presence of litter, the reflectance spectrum of the target litter itself is very important information to identify the kind of litter, which will be discussed in this presentation.