Non-invasive, opto-acoustic water current measurement system and method

The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. A method and system are provided for measuring water current. An acoustically-modulated beam of radiation is transmitted to a target location on the surface of a body of water. As the beam transits the water, acoustic radiation propagates away from the beam towards the surface and experiences a Doppler shift in frequency relative to the acoustic frequency used for modulation. The Doppler shift is caused by current in the water through which the acoustic radiation transits. The Doppler-shifted frequency is measured as an indication of water current.