A coherent marine radar for decameter-scale current mapping and direct measurements of directional ocean wave spectra

A coherent marine radar with 6-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. Such a system allows the direct measurement of the ocean wave spectrum by means of 3D-FFT processing of a sequence of coherent radar images collected at a 0.4 Hz image rate. Typically, 256 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 in the scene. A pair of such radars operated at a coastal site, separated by a few hundred meters along the coastline, allows the combination of radial components to be combined into a mean current vector field. Results of first testing of the radar are presented for a field site at the U.S. Army Corps of Engineers Field Research Facility, Duck, N.C.