Variability of directional spectra of wind-generated waves, studied by means of wave staff arrays

Parameterization of the directional distribution of the wave energy obtained by means of arrays of wave probes is suggested. The parameterization encompasses a wide frequency band both above and below the peak frequency as well as a broad range of wave ages. The parameterization is developed for the integral width of the directional spectrum, which does not depend on a specific form of the approximating function. The width of the directional distribution depends on the stage of wave development and relative frequency. The narrowest directional spectra are observable, on average, 5% below the peak frequency. Above that frequency, the width of the directional spectrum increases as the frequency rises, and the rate of widening does not depend on the wave age. On the forward face of the spectrum, the rate of widening of the directional distributions towards low frequencies depends strongly on the stage of wave development and, at early stages, the directional spectra in this range are unchangeable. In general, the directional distributions of wave energy become narrower as the waves develop.