Abstract: The invention provides navigational aid for use on board remotely operated r autonomous underwater vehicles. A pulsed laser light signal is directed to the ocean bottom where it is reflected back to a tracking camera located on board the vehicle. The time required for the pulsed light signal to be detected by the camera provides the information from which an on board computer can compute the vehicle's altitude. The camera is range gated and synchronized with the laser. Successive images provided by the reflected laser light are correlated by an image processing program. A correlation function applied to the output of the image processing program provides data from which the computer can calculate the vehicle's movement. An electronic clock provides a time base that is input to the computer in order to derive the vehicle's velocity. Velocity and position data may then be made available for navigation and vehicle control.