A system and method of non-intrusive anemometry. The system comprises an acoustic transmitter disposed at a boundary of fluid flow and first and second acoustic receivers adapted to receive transmissions from the acoustic transmitter. A processor is coupled to the acoustic receivers to determine the time of arrival of the transmission at the acoustic receivers. The acoustic transmitter and acoustic receivers are arranged such that the acoustic transmitter is upstream from the first acoustic receiver which is in turn upstream from the second acoustic receiver.