DEVELOPMENT OF ACCURATE, RELIABLE AND ROBUST ESTIMATION METHOD OF DIRECTIONAL SPECTRUM FROM FIELD DATA OBSERVED WITH ULTRASONIC DOPPLER-TYPE DIRECTIONAL WAVE METER

There are several methods for the observation and analysis of directional spectra. Regarding observations, independent wave quantities have been measured using buoys or PUV instruments, and the directional spectrum has been estimated. However, estimating an accurate directional spectrum solely from these three wave quantities is challenging. Therefore, since the 1990s, observations using ultrasonic Doppler-type directional Wave Meters (DWM) have been conducted in Japan (Hashimoto, et al., 1996). DWM can increase the amount of information necessary for estimating the directional spectrum by increasing the number of layers of water particle velocity observations. Unfortunately, increasing the number of observation layers in DWM does not necessarily lead to better accuracy or stability of the directional spectrum. In other words, as the amount of information increases, there can be an unexpected increase in the concentration of directional energy, suggesting the need for further improvements (Hashimoto, et al., 2019).