Sandy shoals in certain near shore areas shift continuously and present a danger to navigation. It is logistically impossible to keep nautical charts current using the traditional survey methods when the bottom contours change so rapidly. NOAA’s Office of Coast Survey leverages remote sensing data in new ways to derive bathymetry for the purposes of updating nautical charts in dynamic coastal areas. An exciting new method Coast Survey is exploring is X-band radar wave imaging. Marine radar is not a new technology, however, there are advantages to exploring old technology for new purposes. Many NOAA vessels and other coastal installations are already equipped with the hardware to facilitate this type of data acquisition.
Radar wave imaging uses backscattered radar intensity to create remotely sensed images of waves. So how do we derive bathymetry from wave images? The shape and depth of the seafloor—whether rocky or sandy, shoal or deep—influences surface currents, as well as the character and speed of waves, and swell. Radar backscatter processing over time yields a series of coherent images of the wave field. By simply averaging the images of waves over a period, it is possible to depict the general shape of the seafloor bathymetry. Additional processing of the coherent wave-speed images produces derived depths.
To determine the value of using radar as a method for deriving water depths in near shore areas, NOAA teamed up with the Korean Hydrographic and Oceanographic Agency (KHOA), Oregon State University, and the private company Areté Associates. NOAA contracts awarded through the Small Business Innovation Research (SBIR) program funded Areté Associates for the research and development of X-band radar bathymetery technology. SBIR is a competitive program that enables domestic small businesses to engage in federal research and development that has the potential for commercialization.
NOAA conducted radar bathymetry activities in two locations, the Oregon coast using Oregon State University’s X-band radar installed atop the U.S. Coast Guard Station Yaquina Bay tower; and Beaufort, North Carolina, using a temporary X-band radar installation at the U.S. Coast Guard Station Fort Macon near the Beaufort Inlet.
To explore the potential for wide-use and commercialization of the radar data, Areté created a real-time cloud service to automatically process regular uploads of nonproprietary radar data to produce raw and time-averaged radar images and movies, bathymetry and uncertainty grids, and water levels. This method presents potential for planning with regional navigation services field teams because they can easily collect radar data and process it in the cloud, eliminating the need for extra software, a technician, or even training requirements. Further, using the cloud service makes subsequent commercialization of the data easier for third-party developers.
The following is a video of time averaged X-band radar of Beaufort Inlet, North Carolina. This video is a product of Areté’s cloud-based processing service. Each frame of the movie represents a 15-minute average of the radar backscatter (or images of waves). Notice the evidence of shoaling just outside the entrance to the inlet. Additional processing of the coherent wave-speed images produces derived depths.