Chad Whelan

The Integrated Ocean Observing System High-Frequency Radar Network: Status and Local, Regional, and National Applications

A national high-frequency radar network has been created over the past 20 years that provides hourly 2-D ocean surface current velocity fields in near real time from a few km offshore out to approximately 200 km. This preoperational network is made up of more than 100 radars from 30 different institutions. The Integrated Ocean Observing System efforts have supported the standards-based ingest and delivery of these velocity fields to a number of applications such as coastal search and rescue, oil spill response, water quality monitoring, and safe and efficient marine navigation. Thus, regardless of the operating institution or location of the radar systems, emergency response managers, and other users, can rely on a common source and means of obtaining and using the data. Details of the history, the physics, and the application of high-frequency radar are discussed with successes of the integrated network highlighted.

A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network

In order to address the need for surface trajectory forecasts following deployment of coastal HF radar systems during emergency-response situations (e.g., search and rescue, oil spill), a short-term predictive system (STPS) based on only a few hours data background is presented. First, open-modal analysis (OMA) coefficients are fitted to 1-D surface currents from all available radar stations at each time interval. OMA has the effect of applying a spatial low-pass filter to the data, fills gaps, and can extend coverage to areas where radial vectors are available from a single radar only. Then, a set of temporal modes is fitted to the time series of OMA coefficients, typically over a short 12-h trailing period. These modes include tidal and inertial harmonics, as well as constant and linear trends. This temporal model is the STPS basis for producing up to a 12-h current vector forecast from which a trajectory forecast can be derived. We show results of this method applied to data gathered during the September 2010 rapid-response demonstration in northern Norway. Forecasted coefficients, currents, and trajectories are compared with the same measured quantities, and statistics of skill are assessed employing 16 24-h data sets. Forecasted and measured kinetic variances of the OMA coefficients typically agreed to within 10–15%. In one case where errors were larger, strong wind changes are suspected and examined as the cause. Sudden wind variability is not included properly within the STPS attack we presently employ and will be a subject for future improvement.

Expanding maritime domain awareness capabilities in the arctic: High Frequency radar vessel-tracking

The arctic could be ice free during the summer by as early as 2040 [1]. This could alter the dominant shipping routes between Europe and Asia. The ability to monitor this traffic is hindered by lack of sensors, communication and power for the sensors. SeaSonde High Frequency radars were installed along the northwest corner of Alaska from July to December 2012. These radars were able to make simultaneous measurements of ocean surface currents as well as measure the position and velocity of vessels passing by the radar. This successful demonstration proves that High Frequency radar can be a valuable tool for providing maritime domain awareness and persistent surveillance capabilities in the arctic.

Measuring Antenna Patterns for Ocean Surface Current HF Radars with Ships of Opportunity

AbstractHF radars measure ocean surface currents near coastlines with a spatial and temporal resolution that remains unmatched by other approaches. Most HF radars employ direction-finding techniques, which obtain the most accurate ocean surface current data when using measured, rather than idealized, antenna patterns. Simplifying and automating the antenna pattern measurement (APM) process would improve the utility of HF radar data, since idealized patterns are widely used. A method is presented for obtaining antenna pattern measurements for direction-finding HF radars from ships of opportunity. Positions obtained from the Automatic Identification System (AIS) are used to identify signals backscattered from ships in ocean current radar data. These signals and ship position data are then combined to determine the HF radar APM. Data screening methods are developed and shown to produce APMs with low error when compared with APMs obtained with shipboard transponder-based approaches. The analysis indicates tha...

Automatic calibrations for improved quality assurance of coastal HF radar currents

CODAR Ocean Sensors, Ltd. and the University of California, Santa Barbara are developing a method by which HF radar antenna response patterns can be calibrated automatically over time. Currently, over 130 HF radar units are providing coastal surface current maps to the public via the U.S. Integrated Ocean Observing System (USIOOS): http://www.ioos.gov/hfradar/. These real-time data are used for Coast Guard Search and Rescue, Hazardous Materials Spills Response, Water Quality Monitoring, Monitoring Harmful Algal Blooms, Fisheries Management, Modeling, Marine Navigation, Ocean Energy Production. Techniques for improved, automated quality assurance of the data provided by coastal radar stations, such as the one discussed here, will improve the efficacy of efforts in these areas. Passing vessels provide a steady supply of targets for which the echoes in the HF Doppler spectra can be used as source signals. The Automatic Identification System (AIS) transmissions from these vessels provide the position and, therefore, bearing to the vessel. By associating the known AIS positions with HF Doppler echoes, a low-cost calibration procedure can be implemented which can reduce or eliminate more labor-intensive alternatives. This method is demonstrated using data from mid-range systems in the Santa Barbara channel that are operating in the 13 MHz band. A prototype package has been deployed on a system monitoring the Gulf of Farallones and the shipping lanes approaching the San Francisco Bay. Performance and data quality metrics for this prototype will be discussed.

High Frequency radar measurement resiliency with bistatics

Increasing the resiliency of High Frequency radar measurements has been a priority within the community for the past several years. One method to increase resiliency is through the use of a bistatic radar configuration, which is unique to the SeaSonde HF radar. This is achieved by separating the transmit and receive stations and then linking them through the Global Positioning System (GPS) reference time signal. A study was undertaken to determine the impact of bistatic data on the surface current measurements of the Mid Atlantic Bight. Simulation software was used to model different permutations of transmit and receive stations to determine if there was an optimal configuration. The software modeled the Geometric Dilution of Statistical Accuracy (GDOSA) of the HF radar coverage area. GDOSA describes regions where combination from radials to totals is of high accuracy because the crossing angle between measurements from two different radars is orthogonal. The converse to this are regions where the total vector measurement are of low accuracy because the measurements from two different radars are nearly parallel. The scenarios tested included the bistatic measurements from the adjacent two, three and four stations on either side of a receive station. The simulation was applied to the 5, 13 and 25 MHz networks that are operated as part of the Mid Atlantic Regional Association Coastal Ocean Observing System (MARACOOS). We also simulated radars being offline to determine if any were more critical than others. Initial findings indicate that the area of highest data quality can be increased by a factor of five when the network is fully bistatic. The use of three or four adjacent radars did not increase the coverage compared to the adjacent two radars. The results of the site outage tests indicated that the loss of certain sites could reduce the coverage of the network by as much as 55%. The results found here have implications for the approximately 300 High Frequency radars that are in operation around the globe. With the addition of a hardware and software to make the network bistatic the coverage area with the highest accuracy can be increased by a dramatic amount.

Rapid deployable HF RADAR for Norwegian emergency spill operations

The Norwegian company CodarNor A/S, with funding from the Norwegian Clean Seas Association for Operating Companies (NOFO) and from Innovation Norway through an industrial research and development contract, is developing a self-contained rapid deployment HF radar which can be deployed by helicopter or other means to remote and rugged locations along the Norwegian coast and operate autonomously, communicating surface current data in real time back to operators, the Norwegian Coastal Administration and drift modelers. Large-scale 2-D current maps collected from these rapid-deployable systems will be used to improve spill response efforts by blending data with drift model currents for improved drift predictions and cleanup vessel management.

Benefits of multi-static on HF Radar networks

Multi-static surface current vector data was processed for two different HF Radar networks, one measuring currents off the East Coast of the U.S. and the other measuring currents in the Malta Channel. Some effects of adding multistatic data are shown, including decreases in 2-D total vector uncertainties, increase in percent coverage within the network grid and increases in HF radar coverage area.