Measuring the space and time evolution of the geometric, kinematic and dynamic properties of oceanic breaking waves

本项目的总体目标是为海洋学、大气科学和工程学目的提供对海洋破碎波的更好理解和描述。海洋表面的破碎波代表了海洋-大气界面上发生的最极端的流动：它们产生高水平的上层海洋湍流，将空气带入水柱，这驱动气泡介导的气体和气溶胶颗粒的海-气交换，分散污染物和营养物，改变最大波高和波峰高度统计数据，并可对海洋环境中的结构物产生巨大的砰击力。因此，破碎波调制上层海洋和表面波场的能量，驱动海洋-大气界面交换，影响天气和气候动力学以及影响工程设计。由于破碎波在海洋表面的间歇性发生，伴随着高流体速度和高空气分数，海洋中破碎波的详细现场测量是非常罕见的。因此，人们对个别海洋破碎波的可能性、规模和严重程度知之甚少。此外，与破碎波相关的复杂流体动力学使得精确的数值模拟具有高度挑战性和计算成本。为了应对这些挑战，该项目寻求开发一种基于数字图像的遥感方法，通过测量单个破碎波产生的时空演变的白顶泡沫信号来描述海洋破碎波的特征。学生将有机会获得从Acqua阿尔塔海洋研究塔（AAT）在亚得里亚海由共同主管Benetazzo收集的立体视觉海面图像的多年数据集。这些图像提供了一个详细的测量的时间演变的3-D海面高程场在一个大面积的海洋表面，从中可以计算出方向波谱。在项目过程中，学生将通过在AAT上安装额外的摄像设备来获得更多的图像数据集。通过开发定制的数字图像处理算法，学生将分析单个破碎波的几何，运动学和动力学特性，并开发其相关能量耗散的新统计描述。这些结果将得到欧洲中期预报中心（ECMWF）共同主管Bidlot提供的最先进的数值谱波模型数据的补充。学生有机会在项目期间与ECMWF密切合作。ECMWF的建模部分代表了实地研究结果可以在全球范围内应用的途径，因此代表了工作的一个关键组成部分。学生将有机会应用破碎波的场分析产生的结果来估计破碎波驱动的气泡介导的空气-使用ECMWF波浪模式在全球尺度上的二氧化碳浓度和气溶胶产生通量的海洋通量。收集的破波数据将使学生能够开发破波描述，可以告知近海工程设计标准。因此，该项目为学生提供了一个独特的机会，与具有一系列专业知识的主管合作，并为与几个不同学科相关的破波描述做出重要的突破性贡献。

The overarching goal of this project is to provide a better understanding and description of oceanic breaking waves for oceanographic, atmospheric science and engineering purposes.Breaking waves at the ocean surface represent the most extreme flow occurring at the ocean-atmosphere interface: they generate high levels of upper ocean turbulence, entrain air into the water column which drives bubble-mediated air-sea exchange of gas and aerosol particles, disperse pollutants and nutrients, alter maximum wave height and crest height statistics and can generate large slamming forces on structures in the marine environment. Consequently breaking waves modulate the energy of the upper-ocean and surface wave field, drive ocean-atmosphere interfacial exchanges that influence weather and climate dynamics and impact engineering design.Due to their intermittent occurrence at the ocean surface, associated high fluid velocities and high air fractions, detailed in-situ measurements of breaking waves in the ocean are extremely rare. Consequently, relatively little is known about the likelihood, scale and severity of individual oceanic breaking waves. Moreover, the complex hydrodynamics associated with breaking waves make accurate numerical simulations highly challenging and computationally expensive. To address these challenges, this project seeks to develop a digital image-based remote sensing approach to describe the characteristics of oceanic breaking waves by measuring the space-time evolving whitecap foam signal generated by individual breaking waves. The student will have access to a multi-year dataset of stereovision sea surface images gathered from the Acqua Alta oceanographic research Tower (AAT) in the Adriatic Sea by co-supervisor Benetazzo. These images provide a detailed measurement of the time-evolving 3-D sea surface elevation field across a large area of ocean surface, from which directional wave spectra can be calculated. Further image datasets will be obtained by the student through the installation of additional camera equipment on the AAT during the course of the project. Through the development of bespoke digital image processing algorithms, the student will analyse the geometric, kinematic and dynamic properties of individual breaking waves and develop new statistical descriptions of their associated energy dissipation. These results will be complemented with data from a state-of-the-art numerical spectral wave model provided by co-supervisor Bidlot at the European Centre of Medium Range Forecasting (ECMWF). The student has the opportunity of working closely with the ECMWF during the project. The ECMWF modelling component represents the pathway by which the results from the field study can be applied in a global context, therefore representing a key component of the work.The student will have the opportunity to apply the results generated from the field analysis of breaking waves to estimate breaking-wave-driven bubble-mediated air-sea fluxes of carbon dioxide concentration and aerosol production fluxes on a global scale using the ECMWF wave model. The breaking wave data collected will enable the student to develop breaking wave descriptions that can inform offshore engineering design standards. As such, this project offers the student a unique opportunity to work with supervisors with a range of expertise and make important breakthrough contributions to the description of breaking waves relevant to several diverse disciplines.