An upgraded submerged Doppler-type directional wave meter can measure 10wave quantities related to directional wave motions, i.e. water surface elevation, 3 components of water particle velocities at each layer of 3different water depth ranging from shallow to deep. In this study, accuracy of directional spectrum estimation is comprehensively investigated for various cases where directional spectra are estimated with various sets of different number of wave quantities. As a result, accuracy

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... ovement is generally confirmed in various wave conditions when all the quantities are applied to the estimations, compared with the cases where conventional 4 wave quantities are applied to the estimations. G