Spectral and time-domain comparison of GNSS and accelerometer wave buoys

A comparison of spectral and time-domain wave observations collected by accelerometer-based Datawell Waverider and Global Navigation Satellite System (GNSS) based Sofar Spotter wave buoys is presented over nearly 24,000 hours at two sites in the Southern and Indian oceans. All buoy data were processed consistently using the raw displacement time series. Across integrated wave parameters derived from the spectrum, the observations show good agreement; however, based on the computed bias, the Spotter wave heights were slightly smaller at the Southern Ocean site (Datawell Waverider 4) and slightly larger at the Indian Ocean site (Datawell Waverider MkIII). The Waverider buoys showed more energy at frequencies higher than the peak and less at frequencies lower than the peak. The high and low-frequency ends of the spectrum also had different spectral shapes, reflecting the different band-pass filtering methods completed on-board each buoy. The Spotter buoys also consistently reported broader directional spreading. In the time domain, comparison of the significant wave height and mean period is similar to that of the spectral comparison. The Spotter buoys more frequently reported large (unphysical) zero-crossing individual wave heights. This behavior was able to be reproduced when the buoy was momentarily submerged, causing loss of the GNSS satellite signal. Similar to other studies, we also found that at both sites, the Waverider buoys recorded horizontal displacements larger than those recorded by the Spotter and expected by linear theory. Across our complete analysis, the two buoy types reported similar integrated statistics; however, differences emerged when assessing higher-order parameters.