Ocean Sound Speed Profile Measurement Using a Pulse–Echo Technique

This article presents an acoustic method for remotely measuring the ocean sound speed profile using a single directional transmitter and at least two receivers. By employing cross-correlation techniques to estimate the time of flight of echo-received signals, the proposed approach calculates both the average sound speeds and the depths of ocean reflectors, resulting in the estimation of the sound speed profile. To validate the method, simulations are conducted using a ray acoustic propagation model that includes both time-invariant conditions and time-varying statistical effects. Key system parameters, including pulse characteristics, transducer geometry, signal-to-noise ratio, and reflector density, are analyzed. The accuracy of the estimated sound speed profiles is assessed by comparing them with the input profiles used in the simulation model. Using the proposed approach, a nonuniform average sound speed profile is measured with a root-mean-square error of 0.67 m/s up to 125 m, using a 22 m transducer array, highlighting its practicality for ocean sound speed monitoring. Experimental evaluation was conducted with a 7.39-m array in the National Research Council of Canada towing tank (200 m × 12 m × 7 m). The tank results showed a standard deviation below 2.5 m/s up to 20-m range, increasing to 12 m/s at 40 m due to reduced signal-to-clutter ratio in the high-interference environment.