Studies toward the development of accurate directional spectrum estimation method using field observation data

An upgraded submerged Doppler-Type directional Wave Meter (DWM) can measure 31 wave quantities related to directional wave motions, i.e., water surface elevation, 3 components of water particle velocities at each layer of 10 different water depths ranging from shallow to deep. In this study, accuracy of directional spectrum estimation is investigated for various cases where directional spectra are estimated with various sets of different number of wave quantities measured with DWM. As a result, accuracy improvement is confirmed in some wave conditions when more quantities are applied to the estimations, compared with the cases where a few wave quantities are applied to the estimations. On the other hand, it was found that when the directional spectra are estimated by adding the water particle velocity components at the deep water depths, the energy concentration of the direction function tends to be estimated higher in proportion to the number of observation layers of the deeper water particle velocity components. Since this feature should be clarified in investigating characteristics of directional spectra observed with DWM, we will continue further investigation for more accurate and reliable directional spectrum estimation.