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

沿海海洋学旨在了解和量化沿大陆架和跨大陆架转移动量、热量、盐分、营养物质和其他水媒物质(如浮游生物和沉积物)的复杂沿岸流。近地表沿海洋流是由风、潮汐和浮力输入的组合驱动的，这些输入来自海-气热通量以及来自河流和河口的淡水流入。不断变化的风应力、压力梯度和浮力强迫导致高度多变的、空间上复杂的沿岸流，观测起来很有挑战性。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上的海岸流动，但在复杂性较高的地区，这种方法并不总是准确的。该项目寻求通过改进高频雷达的表面流观测来增进对复杂海岸动力学的了解。测向雷达是沿海海洋学中使用最广泛的雷达类型，因为与豆形雷达相比，它的天线结构更简单。然而，当前使用的测向算法的局限性导致了输出中的覆盖间隙和速度误差。在其他科学领域开发的四种现有算法将被检验和测试它们在高频雷达中减少误差的能力。更准确的高频雷达观测可以改进对污染物、油类和鱼苗的跟踪，这些对生态系统监测和人类健康非常重要。海岸警卫队的搜救行动将通过改进高频雷达得出的表面海流而变得更有效率。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。该项目所作的改进将增加高频雷达观测对沿海海洋的基础研究和业务应用的价值，直接造福社会。陆基高频雷达是唯一能够同时分辨时间和空间尺度的仪器，对于以具有成本效益的方式了解沿海环流的运动学和动力学至关重要。高频雷达可以在所有天气条件下以每小时为单位测量沿岸洋流，空间分辨率可达1-6公里至近海200公里。高频雷达的空间分辨率和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表现不佳。这一研究项目将评估在其他学科开发的先进信号处理技术，看其通过雷达模拟和高分辨率海洋环流模型的输出减少误差的潜力。将使用以前经过验证的雷达数据集进行进一步评估，包括固定的3单元CODAR SeaSonde类型系统以及新开发的具有灵活天线配置的8单元系统。作为这一项目的结果，海洋雷达对表层海流的观测将得到改善，从而增进对海岸动力学的了解。由于测向雷达是海洋雷达中应用最广泛的一种类型，提高高频雷达的空间和时间分辨率，减小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.