average_absolute_wave_period (s) = Average absolute wave period = sea_surface_wave_period_from_variance_spectral_density_seconf_frequency_moment
average_wave_direction (degree) = Average wave direction = sea_surface_wave_from_direction
direction_of_the_peak_of_the_spectrum (degree) = direction of the peak of the spectrum = sea_surface_wave_from_direction_at_variance_spectral_density_maximum