A compact representation of ocean wave directionality

The spectrum of the longshore component of shoreward directed momentum flux ($\text{S}{}_{\mathrm{xy}}$) due to ocean waves, taken with the energy spectrum for the same wave field, is shown to provide a compact and useful representation of ocean wave directionality. Records of orthogonal surface slope components are demonstrated to yield an unbiased estimate of $\text{S}{}_{\mathrm{xy}}$. One method for estimation of $\text{S}{}_{\mathrm{xy}}$ using this relationship is investigated. Error analysis provides means for optimal selection of measurement parameters. Experimental verification is provided from laboratory tests and from field comparison with a five-element linear array.