The Ocean Cleanup, Batavierenstraat 15, 3014 JH Rotterdam, The Netherlands; Marine Sensor Systems Group, Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Schleusenstraße 1, 26382 Wilhelmshaven, Germany.
ARGANS Limited FR, 260 Route du Pin Montard - BP234, 06904 Sophia-Antipolis cedex, France.
J Hazard Mater. 2021 Mar 15;406:124290. doi: 10.1016/j.jhazmat.2020.124290. Epub 2020 Oct 16.
We present reflectance measurements collected from virgin and ocean-harvested plastics. Virgin plastics included high and low density polyethylene (HDPE, LDPE), polypropylene (PP) as well as polystyrene (PS). Ocean-harvested plastics were ropes, sheets, foam, pellets and fragmented items previously trawled from the North Pacific Garbage Patch. Nadir viewing angles and plastic pixel coverage were varied to advance our understanding of how reflectance shape and magnitude can be influenced by these parameters. We also investigated the effect of apparent colour of plastics on the measured reflectance from the ultraviolet (UV - 350 nm), visible, near to shortwave infrared (NIR, SWIR - 2500 nm). Statistical analyses indicated that the spectral reflectance of the plastics was significantly correlated to the percentage pixel coverage. There was no clear relationship between the reflectance observed and the viewing nadir angle but dampened materials seemed to be more isotropic (near-Lambertian) than their dry counterparts. A loss in reflectance was also determined between dry and wet plastics. Location of absorption features was not affected by the apparent colour of objects. In general, ocean-harvested plastics shared more identical absorption features (960, 1215, 1440, 1732, 1920 nm) and had lower reflectance intensity compared to the virgin plastics (980 nm). Prospects for satellite retrieval of plastic type and pixel plastic coverage are discussed based on Top-of-Atmosphere (TOA) signal simulated through radiative transfer computation using the documented plastic reflectances. Non-linear relationships between TOA reflectance and plastic coverage were observed depending on wavelength and plastic type. Most of the plastics analysed impact significantly the TOA signal but two plastic types did not produce strong signal at TOA (hard fragments, LDPE). Nevertheless, all plastic types produced detectable signals when observations were simulated within the sunglint direction. The measurements collected in this study are an extension to available high quality spectral reference libraries and can support further research in developing remote sensing algorithms for marine litter.
我们展示了从原始和海洋采集的塑料中收集的反射率测量结果。原始塑料包括高密度聚乙烯（HDPE，LDPE）、聚丙烯（PP）以及聚苯乙烯（PS）。海洋采集的塑料包括绳索、薄片、泡沫、颗粒和以前从北太平洋垃圾带拖网捕捞的碎片物品。我们改变了天顶角和塑料像素覆盖率，以深入了解这些参数如何影响反射率的形状和幅度。我们还研究了塑料表观颜色对从紫外线（UV-350nm）、可见光、近短波红外（NIR，SWIR-2500nm）测量的反射率的影响。统计分析表明，塑料的光谱反射率与像素覆盖率的百分比显著相关。观察到的反射率与视场天顶角之间没有明显的关系，但潮湿的材料似乎比干燥的材料更各向同性（接近朗伯）。还确定了干塑料和湿塑料之间的反射率损失。吸收特征的位置不受物体表观颜色的影响。一般来说，与原始塑料相比，海洋采集的塑料具有更多相同的吸收特征（960、1215、1440、1732、1920nm），反射率强度较低（980nm）。根据使用记录的塑料反射率通过辐射传输计算模拟的大气顶（TOA）信号，讨论了基于卫星检索塑料类型和像素塑料覆盖率的前景。观察到 TOA 反射率与塑料覆盖率之间存在非线性关系，这取决于波长和塑料类型。分析的大多数塑料对 TOA 信号有显著影响，但两种塑料类型在 TOA 处没有产生强信号（硬碎片、LDPE）。然而，当在日光反射方向模拟观测时，所有塑料类型都产生可检测的信号。本研究中收集的测量结果扩展了可用的高质量光谱参考库，可以支持开发用于海洋垃圾的遥感算法的进一步研究。
