Variations in directional wave parameters obtained from data measured using a GNSS buoy

This study investigated variations in directional wave parameters by using various combinations of the GNSS buoy data, such as the displacements (enη) and the velocities (uvw) in the east, north, and upward directions. The investigated directional wave parameters included mean wave direction, directional spreading, directional wave spectrum, and dominant wave direction (DWD). The three combinations of GNSS buoy data for determining the directional wave parameters were ηuv, enη, and uvw. Our results revealed that when the significant wave height (H_S) values are ≥ 1 m, the signal-to-noise ratios (SNRs) for various measured items are sufficiently large, such that the directional wave parameters obtained from various data, such as enη, uvw, and ηuv, are identical. By contrast, under smooth to slight sea conditions with an H_S of <1 m, the SNRs for the displacements are small. The small SNRs of enη data tend to produce inaccurate directional wave parameters. The deviation in the mean wave direction and DWD obtained from the enη data compared with those obtained from the uvw and ηuv data decreases as the H_S increases. For small seas, the uvw and ηuv data are more appropriate than the enη data for use in determining directional wave parameters.