ESTIMATING THE DIRECTIONAL SPECTRUM OF WAVES NEAR A REFLECTOR

Near a reflector incident waves are phase-locked to reflected waves an d the wave field is spatially inhomogeneous, while far away from the r eflector such phase-locking is unimportant. In this paper the theoreti cal and practical regions of validity of phase-locked (PL) and non-pha se-locked (non-PL) methods of directional wave analysis methods are in vestigated for both a collocated and a spatially separated configurati on of instruments. A nondimensional framework is developed as a practi cal 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 reflec ted 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 z ones of validity. Equations are presented which predict regions of pot ential uncertainty and directional ambiguities in directional wave spe ctra. A numerical simulation method implemented in this contribution p rovides an effective means of testing the performance of different arr ay geometries.