Comparisons of ADCP and Wave Buoy Collected Wave Measurements.

The purpose of this submission is to examine whether Acoustic Doppler Profilers (ADCPs) can be used as reliable wave gauges by comparing two ADCPs (Workhorse Monitor, 600 Hz) and a surface following buoy (SeaWhatch mini II), deployed during 9 month, in depths from 34 to 40 meters. Despite the distance between them, about 10 km, made difficult an accurate comparison, discrepancies and similitudes found between the ADCPs helped to detect the location influence in the results.

The buoy time series of particles displacement were directly processed for computing the wave spectrums, whereas the wave spectrums based on ADCPs time series of beam velocities were computed by means of the RDI program ‘Wavesmon’. Both procedures used the Iterative Maximum Likelihood Method (IMLM). The same spectral analysis was then applied to the wave spectrums and the outcomes were compared. In addition, the wave spectrums were classified and compared according to specific values of peak period (Tp), peak direction (Dp) and spectral significant wave height (Hm0).

Results of the whole data analysis provided a good agreement between the 3 devices, particularly for the mean period and Hm0, whereas discrepancies for Tp and Dp were significant. Deeper analysis of the classified spectrums and some particular discrepancies showed that differences between peak values were partially dependent on location. However, these analysis together with the high agreement between the two ADCPs for mean frequency direction and normalized frequency spectrum, also described that discrepancies between ADCPs and buoy estimations have a heavily dependence on the wave frequency and the sea state. Indeed these findings corroborate previous studies where it is described that buoys underestimate the wave height at low frequencies, and are unable of discerning peak parameters during simultaneous wave systems with similar peak periods and different peak directions.