Spatial variability of ocean waves, from in-situ measurements

This paper describes the analysis of the spatial properties of ocean waves using measurements from an array of four directional wave buoys installed in a square formation, with side 500 m, in the Celtic Sea, UK. Wave measurements in this area have been installed to support resource assessment and design for wave energy devices at the Wave Hub site off the North Cornwall coast. This unique deployment of multiple directional sensors provides high quality direct measurements of the spatial properties of the wave field. Spectral parameters measured simultaneously by all four buoys within the array are compared and it is demonstrated that wave conditions cannot be considered stationary across the measurement area. Differences in the measured wave fields were observed primarily in the low frequencies and are observed to be of a level sufficient to impact the assessment of site characteristics. Theoretical estimations of refraction and bottom friction indicate that these physical processes contribute to the observed measurements. The results demonstrate the potential effect of spatial variability in wave fields on the monitoring of wave energy sites, and highlight the requirement for accurate evaluation of physical processes.

► Detailed statistical analysis of unique concurrent wave measurements. ► Physical processes distort natural homogeneity of waves at typical wave energy site. ► Physical processes can have a significant effect on wave energy assessments. ► Differences greatest for low freq's, 8.6% difference in Mean incident wave power. ► Short-term spatial variability was largest for high-frequencies, and parameter Tm02.