Ducted impeller wave meters used aboard a light station to observe particle motions in wind waves at various depths beneath the free surface are described. The motions recorded display quasisinusoidal oscillations having an approximate 90° phase shift between the horizontal and vertical velocity components that lie normal to the wave crests....
Shonting, David H.. 1967. "Measurements of particle motions in ocean waves." Journal of Marine Research 25, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1095