On errors in low frequency wave measurements from wave buoys

Floating wave buoys are widely considered as a global standard for wave data. Marine renewable energy presents a relatively new industry for wave measurements, requiring a high level of accuracy for applications including resource assessment, performance assessment and engineering design. This study draws on the unique deployment of four identical wave buoys in close proximity and a period of data from a free-floating buoy to classify spurious low frequency measurements as erroneous. The nature of the occurrence of these errors, and their effect on the validity of measurements are also examined. The work shows that the errors are directly related to the drag forces on the buoy, but with a correctly designed filter, the effect of the errors on the wave measurements can be mitigated. A variable filter process is described which improves the accuracy of measurements captured by these buoys. This is recommended for all interpretation of these data, and is essential for any detailed statistical analysis.