The directional spectrum S(k) [or S(f,θ)] measures the distribution of wave energy in wave number, k, (or frequency, f) and direction. Different contributions to local wave energy, e.g., swell from distant storms and locally wind-generated waves, can be identified in a measurement of the directional spectrum (see Fig. 1). The direction of propagation of wave energy and the period (l/f) of the most energetic waves are important for many practical applications, e.g., the design and operation of coastal and offshore structures and storm surge forecasts.

Wyatt, L.R. 1997. The ocean wave directional spectrum. Oceanography 10(2):85–89, https://doi.org/10.5670/oceanog.1997.31.

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