Coherent marine radar measurements 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 allows direct measurement of the ocean wave spectrum by means of 3D-FFT processing of a sequence of coherent radar images of orbital wave patterns. Currently, with a 2.5-s rotation rate, 256 images cover a period of the order of ten minutes, with frequency alias at 0.2 Hz, with upgrade to 0.4 Hz planned with later units. Radial current maps are obtained by a superposition of all radial velocity images collected. This summing forces orbital wave patterns to blend to the mean, resulting in the map of mean radial current. A pair of such radars operated at a coastal site, separated by a few hundred meters along the coastline, may allow the combination of 2-site radial components to be combined into a mean current vector field. Results of first tests of the first prototype radar measurement of radial current and RMS wavehieght are presented for a field site at the U.S. Army Corps of Engineers Field Research Facility, Duck, N.C.