Collaborative Research: Resolving complex coastal flows via advances in high-frequency radar

沿海海洋学旨在了解和量化复杂的沿海流动，这些流动在沿着和跨越大陆架传递动量、热量、盐、营养物质和其他水生物质，如浮游生物和沉积物。 近地表沿海洋流是由风、潮汐和浮力输入的组合驱动的，浮力输入是由于海气热通量和来自河流和河口的淡水流入。不断变化的风应力、压力梯度和浮力迫使导致高度可变的、空间复杂的海岸流，这对观测是一个挑战。高频（HF）雷达是一种广泛使用的海洋学方法，用于研究大空间尺度的海岸流，但在复杂性较高的地区，这种方法并不总是准确的。该项目旨在通过改进高频雷达的表面电流观测来增进对复杂海岸动态的了解。定向雷达是沿海海洋学中使用最广泛的雷达类型，因为它的天线配置比波束形成雷达更简单。然而，目前的测向算法的局限性，导致覆盖间隙和速度误差的输出。四个现有的算法，已在其他科学领域的发展将被检查和测试，以减少在高频雷达误差的能力。更精确的高频雷达观测可以改善对污染物、石油和鱼苗的跟踪，这对生态系统监测和人类健康至关重要。海岸警卫队的搜索和救援行动将通过改进高频雷达衍生的表面电流而变得更加有效。该项目支持跨学科合作，将工程师和海洋学家聚集在一起，并培训本科生和研究生。此外，研究结果还将与在美国沿海地区运营和使用高频雷达的政府机构、利益相关者和社区领导人分享。这一项目所作的改进将提高高频雷达观测的价值，用于沿海海洋的基础研究和直接造福社会的业务应用。陆基高频雷达是唯一能够以成本效益高的方式解决时间和空间尺度对了解沿海环流的运动学和动力学至关重要的仪器。高频雷达可以在所有天气条件下以低于每小时的时间尺度测量沿海海流，空间分辨率为1-6公里，离岸达200公里。高频雷达的空间分辨率和作用距离取决于发射频率和带宽。传统的测向雷达数据解译算法在复杂的沿海地区效果不佳。该研究项目将评估其他学科开发的先进信号处理技术，以通过雷达模拟和高分辨率海洋环流模型的输出来减少误差。将使用以前验证的雷达数据集进行进一步评估，包括固定的3单元CODAR海洋探测器型系统以及新开发的具有灵活天线配置的8单元系统。由于这一项目，海洋学雷达对表层海流的观测将得到改进，从而增进对沿海动态的了解。由于测向雷达是最广泛使用的海洋雷达类型，提高高频雷达的空间和时间分辨率并减少误差将产生广泛的影响。

Coastal oceanography aims to understand and quantify the complex coastal flows that transfer momentum, heat, salt, nutrients and other waterborne materials, such as plankton and sediment, along and across the continental shelf. Near-surface coastal ocean currents are driven by a combination of winds, tides, and buoyancy inputs due to air-sea heat fluxes and freshwater inflows from rivers and estuaries. Changing wind stress, pressure gradients, and buoyancy forcing lead to highly variable, spatially complex coastal currents that are challenging to observe. High frequency (HF) radar is a widely used oceanographic approach to study coastal flows across large spatial scales but in areas of higher complexity, this method is not always accurate. This project seeks to advance knowledge of complex coastal dynamics by improving surface current observations from HF radars. The direction-finding radar is the most widely used type of radar used in coastal oceanography due to its simpler antenna configuration compared to bean-forming radars. However, the limitations of the current direction-finding algorithms used lead to coverage gaps and velocity errors in the output. Four existing algorithms that have been developed in other fields of science will be examined and tested for their ability to reduce error in HF radar. More accurate HF radar observations can improve tracking of pollutants, oil, and fish larvae which are important for ecosystem monitoring and human health. Search and rescue operations by the Coast Guard will be made more efficient through improved HF radar-derived surface currents. This project supports interdisciplinary collaboration bringing engineers and oceanographers together and training of undergraduate and graduate students. In addition, the results will be shared with government agencies, stakeholders and community leaders operating and using HF radars around the U.S. coasts. The improvements made from this project will increase the value of HF radar observations for both basic research in the coastal ocean and operational applications directly benefiting society. Land-based HF radar is the only instrument capable of resolving both the temporal and spatial scales essential for understanding the kinematics and dynamics of coastal circulation in a cost effective manner. HF radars can measure coastal currents in all weather conditions on sub-hourly time scales with spatial resolution of 1-6 km up to 200 km to offshore. The spatial resolution and range of HF radar depend on transmit frequency and bandwidth. The traditional algorithm for interpreting direction-finding radar data does not perform well in complex coastal areas. This research project will evaluate advanced signal processing techniques, developed in other disciplines, for their potential in reducing errors via radar simulations and outputs from a high-resolution ocean circulation model. Further evaluation will be made using previously validated radar data sets including fixed 3-element CODAR SeaSonde-type systems as well as newly developed 8-element systems with a flexible antenna configuration. As a result of this project, surface current observations from oceanographic radar will be improved, thus enhancing understanding of coastal dynamics. Since direction-finding radars are the most widely used type of oceanographic radar, improving the spatial and temporal resolution of HF radars and reducing errors will have a wide impact.