Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor, USA.
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, USA.
Sci Rep. 2023 Feb 3;13(1):1978. doi: 10.1038/s41598-023-29088-9.
We study the flow physics underlying the recently developed remote sensing capability of detecting oceanic microplastics, which is based on the measurable surface roughness reduction induced by the presence of microplastics on the ocean surface. In particular, we are interested in whether this roughness reduction is caused by the microplastics as floating particles, or by surfactants which follow similar transport paths as microplastics. For this purpose, we experimentally test the effects of floating particles and surfactants on surface roughness, quantified by the mean square slope (MSS), with waves generated by a mechanical wave maker or by wind. For microplastics, we find that their effect on MSS critically depends on the surface area fraction of coverage. The damping by particles is observed only for fractions above O (5-10%), much higher than the realistic ocean condition. For surfactants, their damping effects on both mechanically generated waves and wind waves are quantified, which are shown to be much more significant than that by microplastics. Several new mechanisms/relations for roughness damping by surfactants are also identified. The implications of these experimental results to remote sensing are discussed.
我们研究了最近发展起来的海洋微塑料遥感能力的流动物理学基础，该能力基于海洋表面微塑料存在引起的可测量表面粗糙度降低。特别是，我们感兴趣的是这种粗糙度降低是由浮在水面上的微塑料引起的，还是由与微塑料具有相似传输路径的表面活性剂引起的。为此，我们通过机械造波机或风产生的波浪，实验测试了浮粒子和表面活性剂对表面粗糙度（用均方斜率 MSS 量化）的影响。对于微塑料，我们发现它们对 MSS 的影响取决于覆盖率的表面积分数。仅当分数高于 O（5-10%）时才观察到粒子的阻尼作用，这远高于现实海洋条件。对于表面活性剂，我们量化了它们对机械产生的波浪和风浪的阻尼效应，结果表明它们的阻尼作用远大于微塑料。还确定了几个用于表面活性剂粗糙度阻尼的新机制/关系。讨论了这些实验结果对遥感的意义。
