Coherent marine radar measurements of directional wave spectra using vertically polarized antennas

A coherent marine radar has been developed for imaging ocean wave orbital wave velocity wave patterns. A NOPP program, Roadmap: Technologies for Cost Effective, Spatial Resource Assessments for Offshore Renewable Energy, has helped finance recent ISR studies. This new coherent radar provides a direct measurement of ocean wave orbital wave velocity without relying on a modulation transfer function (MTF) that has been used with previous systems that map radar echo intensity. The latter approach is prone to error due to environmental dependencies of the MTF, particularly when winds blow into incoming waves, which then produces an enhanced echo strength that is misinterpreted by the MTF scaling as due to larger wave slopes and heights. With this new direct measurement of orbital wave velocity, directional ocean wave spectra can be measured unambiguously, and deterministic ocean wave height fields that can be mapped for real-time input into wave forecasts for ship motion response applications. Results of experiments conducted at the USACE pier in Duck, NC, during the passage of Hurricane Irene are presented, showing the effect of using vertically polarized antennas, minimizing wave breaking effects for wave heights above 2.5 m.