Mean Point Seawater Velocity refers to the velocity (speed and direction) of a single "point" of water (in this case, a volume of several square meters) averaged over time-scales associated with surface gravity waves. This instrument estimates water velocity by measuring the Doppler shift of acoustic signals reflected by particles suspended in the water. This data product is the northward component of mean point seawater velocity in earth coordinates relative to true north (accounted for magnetic variation).