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HF radar provides valuable ocean data
Technology can map ocean currents, wave heights and vessels over wide area, to help with spill response and SAR activities
Alan Bailey Petroleum News
Radar systems that use high frequency radio waves have established a crucial role in monitoring ocean surface conditions and are now considered a key component in the toolkit for responding to an offshore oil spill response, Hank Stascewich from the University of Alaska Fairbanks told the Alaska Oil Spill Technology Symposium on March 29. The technology can also be of significant help in an offshore search and rescue operation, Stascewich said.
Offshore monitoring HF coastal radar, commonly referred to as CODAR, or Coastal Oceanic Dynamics Applications Radar, uses radio frequencies somewhere between the frequencies of FM and AM radio and is positioned at a coastal site, from where it can monitor huge areas of the offshore. The distance from the radar site that can be monitored depends on the radio frequency used but can go out to more than 180 kilometers. Essentially the salt water of the ocean causes what is referred to as Bragg scattering from the transmitted signal, a phenomenon that results in a signal at half the wavelength of the transmitted signal being returned to the radar receiver. The returned signal enables a measurement of the rate of movement of ocean waves: Any difference between the wave velocity and the theoretical velocity of the waves then represents the speed of the ocean current. By triangulating the data from two different radar stations, it is possible to determine both the speed and direction of the currents across a wide area, Stascewich explained.
Extraction of part of the incoming data also enables accurate determinations of wave heights, and the monitoring of the locations of vessels operating in the area of the radar coverage.
Oil spill response The prime value of the radar in support of an oil spill response is in predicting the trajectory of an oil slick. In conjunction with meteorological wind data, the ocean current data can enable an estimation of the speed and direction for the spread and movement of a slick. In fact, HF radar sites around the U.S., including Alaska sites, feed data into the National Oceanic and Atmospheric Administration’s oil spill response computer system, Stascewich said.
In the event of an offshore search and rescue operation, the radar data can enable predictions of the drift movement of, say, a person overboard, thus enabling a significant reduction of the required search area.
HF radar data for Alaska’s Beaufort and Chukchi seas are gathered hourly, with statistical techniques then used to analyze the meaning of the vast amount of data collected. The data provides insights into phenomena such as the influence of winds on ocean mixing patterns, and the relative influence of water from the Arctic and Pacific oceans.
Vessel monitoring In an era when steadily increasing vessel traffic in the Arctic is a cause for concern, the HF radar data can be used to spot the presence of any vessels that are not transmitting marine identification information. For example, in 2014 an Alaska HF radar system picked up on the presence of an unidentified Russian naval vessel inside the U.S. exclusive economic zone, Stascewich said.
Although there are many HF radar installations around the coastline of the Lower 48, there are just three stations currently operating around the northwest coast of Alaska, Stascewich said. One challenge in Alaska is the general lack of a power supply at remote coastal locations - an HF radar system uses a lot of power and has to run continuously. Researchers at UAF developed a power module that uses renewable energy and has been powering an HF radar system at Point Barrow for eight years. The plan now is to design a more compact module that can be shipped by helicopter and can be operational within six hours, ready for deployment in the event of an oil spill, Stascewich said.
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