"SDN:P07::CFV8N70" . . . "2008-04-15 14:00:00.0" . "SDN:P07::CFV8N70" . . . . "accepted"@en . . . "1" . . "false" . . "2008-04-15 14:00:00.0" . "The swell wave directional spectrum can be written as a five dimensional function S(t,x,y,f,theta) where t is time, x and y are horizontal coordinates (such as longitude and latitude), f is frequency and theta is direction. S can be integrated over direction to give S1= integral(S dtheta). Frequency moments, M(n) of S1 can then be calculated as follows: M(n) = integral(S1 f^n df), where f^n is f to the power of n. The first wave period, T(m1), is calculated as the ratio M(0)/M(1)."@en . "" . "SDN:P07::CFV8N70" . . . "1" . "sea_surface_swell_wave_mean_period_from_variance_spectral_density_first_frequency_moment"@en .