| 摘要 |
A system adapted for the measurement of ship's speed by utilizing the doppler shift imparted to sonic energy reflected from the bottom of a body of water or from sources of reflection within the water itself. Pulsed sonic transmissions are directed from the ship at an angle to the vertical to provide a forward or aft component to the received doppler frequency signal. The received signal is translated to an intermediate frequency lower than the received frequency and the elapsed time of a predetermined number of cycles at the intermediate frequency in each of a succession of received pulse signals is measured. After ascertaining the equality of successive ones of these measurements, the system provides for the storing of successive ones of these measurements and the generation of a periodic pulse train signal having a frequency dependent on these measurements. The pulses of the pulse train wave are then counted during fixed time intervals to provide a number representing the doppler frequency shift and the corresponding speed of the ship. |
