Estimating the directional spectrum of waves near a reflector

Near a reflector incident waves are phase-locked to reflected waves and the wave field is spatially inhomogeneous, while far away from the reflector such phase-locking is unimportant. In this paper the theoretical and practical regions of validity of phase-locked (PL) and non-phase-locked (non-PL) methods of directional wave analysis methods are investigated for both a collocated and a spatially separated configuration of instruments. A nondimensional framework is developed as a practical guide for the application of these methods in terms of L/S and T/S. Here L is the nondispersive time lag between the incident and reflected time series, S is the segment length of the fast Fourier transform, and T is the wave period. Numerical tests reveal that it is possible to use both methods with acceptable errors beyond their theoretical zones of validity. Equations are presented which predict regions of potential uncertainty and directional ambiguities in directional wave spectra. A numerical simulation method implemented in this contribution provides an effective means of testing the performance of different array geometries.