An embodiment provides a method for measuring velocity of fluid flow in a channel, including: transmitting, using a transmitter, directed energy carrying a signal toward a surface of a fluid in a fluid channel so as to produce a plurality reflections from locations substantially spanning the entire width of the fluid channel; detecting, using a plurality of measurement beams, received signals from the plurality of reflections so produced; determining, based upon differences between transmitted and received signals, a plurality of localized velocities; and computing, from the plurality of localized velocities, a cross-sectional average velocity of fluid in the channel. Other embodiments are described and claimed.