Comparison of oil slick and drifter motion at OHMSETT wave tank

In the aftermath of the Deepwater Horizon oil spill, thousands of ocean drifters were deployed in order to better understand the pathways and dispersion processes that drive oil slicks from the deep ocean to the coastline. Most of the drogued drifters released had a 0.60 m draft, hundreds of undrogued drifters had a 0.05 m draft, and thousands of drifting bamboo plates had a draft of 0.017 m. But typical slick thickness is 0.01 m or less, which raised an important question to interpret the ocean datasets correctly: how drifters move compared to oil slicks? The experimental study presented here addresses this issue by quantifying the differences, in terms of advection and diffusion, between the motion of oil slicks and the three groups of drifters mentioned above. Oil and drifters were released side-by-side in a vertically sheared flow controlled by waves produced in the National Oil Spill Response Research and Renewable Energy Test Facility (OHMSETT) wave-tank in April 2016. Trajectories were recorded by an aerial camera with spatial accuracy of 1.5 cm. The trajectories of each material patch were analyzed in details to determine how fast they were advected, but also how fast they spread and in which direction.

在深水地平线（Deepwater Horizon）原油泄漏事件发生后，为更精准地解析将浮油从深海输送至海岸的输运路径与扩散过程，科研人员部署了数千套海洋漂流浮标（drifter）。本次投放的浮标中，多数带沉子的漂流浮标吃水深度为0.60米，数百套无沉子漂流浮标吃水深度为0.05米，另有数千套漂流竹板的吃水深度为0.017米。但常规浮油的厚度仅为0.01米甚至更薄，这一差异提出了一个关乎海洋数据集正确解读的关键问题：漂流浮标的运动与浮油的运动存在何种差异？本项实验研究通过量化浮油与上述三类漂流载体在平流输运（advection）与扩散（diffusion）过程中的运动差异，解答了上述问题。2016年4月，研究团队在国家溢油响应研究与可再生能源试验设施（National Oil Spill Response Research and Renewable Energy Test Facility, OHMSETT）的波浪水槽中，于波浪驱动的垂直剪切流环境内同步投放浮油与漂流浮标。研究采用空间精度达1.5厘米的航空相机记录各载体的运动轨迹，并针对每个物质团簇的运动轨迹展开详细分析，以明确其平流输运速率、扩散速率及扩散方向。