The E(f, u) is often estimated (Kuik et al. 1988; Herbers et al. 2012; Thomson et al. 2018) by computing the phasing between the vertical and horizontal motion of surface waves in the cross-spectra. In this study, the unfiltered voltage measurements H in each window are used to derive the horizontal velocity of surface waves [u and y in Eq. (7)]. Combined with the processed vertical acceleration measurements a, the normalized directional moments a1 and b1 can be computed(Thomson et al. 2018) as