Sound Speed Measurement Using Phase Estimation Method of Pulse Signal in Water

The sound speed is one of the indispensable parameters in underwater ranging, positioning, and navigation applications. The accurate measurement of the speed of sound can directly improve the performance of sonar. An accurate measurement method of sound speed in water based on phase estimation is proposed. An acoustic reflector with dual reflecting surfaces is designed, and the sound speed is obtained by measuring the distance between the dual reflecting surfaces and the arrival time delay of the echo signal from the reflecting surfaces. A quadrature phase detection method is proposed to accurately estimate the phase and time delay of the echo signal, and the dual-frequency transmission signal is used to solve the periodic wrapped of the phase estimation. A device for measuring the sound speed in seawater was developed to measure the sound speed of seawater at temperatures of -0.7 °C and 20 °C and a hydrostatic pressure range of 0 MPa to 30 MPa. The maximum standard deviation of the measurement results is 0.022 m/s. The measurement uncertainty of this device is evaluated, and its expanded uncertainty is 0.05 m/s.