Research On Sound Velocity Measurement Approach In Seawater Based On Phase Difference Of Signal

The speed of sound in seawater is one of the important parameters during the measurement of the underwater ultrasonic ranging and positioning, testing and monitoring the marine environment and so on. The propagation speed with the water temperature, pressure and salinity varies. Accurately measure the speed of sound in seawater is important, can be effective for the depth sounder, sonar and other acoustic equipment to provide accurate speed of sound data measurement to correct measurement error.This paper mainly studies the speed of sound measurement in seawater based on phase difference. Critical study of the use of single-frequency signal phase difference estimation method for speed of sound measurement. For phase ambiguity problem of the single-frequency signal, proposed the use of dual-frequency signal phase difference estimation for speed of sound measurement method. The main paper work includes the following aspects:(1) This paper summarizes the distribution of speed of sound in seawater and characteristics, analysis and comparison the current international approach to speed of sound measurement of seawater and characteristics, on the basis of these, using the phase difference estimation for speed of sound measurement method in seawater is proposed in this paper.(2)Proposed a seawater velocity measurement method based on single-frequency signal phase difference estimation. Based on the principle of speed of sound measurement of time difference method, if the time measurement transformed to the phase difference estimate, in the conditions the distance measurement accuracy is high enough, the higher the frequency, the phase difference estimation accuracy requirements lower, the greater the speed of sound measurement accuracy high. In the conditions the signal frequency to determine, the key factor of the speed of sound measurement accuracy is the phase difference estimation accuracy. Therefore, the paper focuses on a variety of phase estimation methods, including zero comparison, digital correlation method and the FFT spectrum analysis. Through analysis and comparison, proposed the use of FFT spectrum analysis as the phase difference estimation method. Established a simplified model of speed of sound measurement system and using the model to analyze their impact on the estimated phase difference. We carried out simulation analysis of speed of sound measurements using single-frequency signal phase difference estimation.(3) Proposed a seawater speed of sound measurement method based on dual-frequency signal phase difference estimation. To solve the phase ambiguity problem for single-frequency signal, getting the higher speed of sound measurement accuracy, this paper proposes the speed of sound measurement methods using a small dual-frequency difference signal, analysis of the measuring principle and the impact of spectral leakage of FFT spectral analysis to the dual-frequency signal phase difference estimation. We carried out simulation analysis of speed of sound measurements using dual-frequency signals phase difference estimation.(4)Building a sound speed of sound measurement experimental system based on the estimated phase difference estimation, the design of signal transmission and signals acquisition hardware circuits, analysis of the impact the experimental platform for distance measurement accuracy to speed of sound measurement accuracy, echo and a variety of environmental factors on the phase difference estimation results. Using the experimental platform to carry out the speed of sound measurement experiment based on the single-frequency signal and the dual-frequency signal phase difference estimation. The experiment data were analyzed and processed to verify the speed of sound measured conclusions for use of signal phase difference estimation.