Coherent marine radar mapping of ocean surface currents and directional wave spectra

A coherent marine radar with 3-m resolution has been developed that measures the radial component of the orbital wave velocity of ocean waves, as well as the mean radial ocean surface velocity. This radar provides a direct measure of the ocean wave spectrum by means of 3D-FFT processing of a sequence of radial velocity images collected at a 0.8 Hz image rate. Typically, 512 images are used, covering periods of the order of ten minutes, allowing a modest number of wave groups to be measured. The mean radial velocity map is obtained by a superposition of all radial velocity images collected, allowing wave patterns to blend to the mean, resulting in a map of mean currents. A pair of such radars operated at a coastal site, separated by a few hundred meters along the coastline, could allow the combination of radial components to be combined into a mean current vector field. Results of an experiment run during the offshore passage of Hurricane Ida in 2009 are presented, collected at the U.S. Army Corps of Engineers Field Research Facility, Duck, N.C.