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

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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.