Temperature-induced sound speed variability in a laboratory water tank

Abstract

Temperature variations in the ocean cause changes in the sound speed and, hence, sound propagation. This project quantified the sound speed variation achievable in a laboratory water tank. The rectangular tank has paneling that minimizes lateral reflections. Two temperature sensors measured the temperature changes over time while the water was cooled with ice, heated, and naturally warmed back to room temperature. Sound speed values were calculated using the freshwater Marczak equation. We found that while the temperature remains relatively uniform near the bottom of the tank during heating and cooling. Heating increases the sound speed at a rate of 3.5 m/s per hour, while adding ice in various quantities decreases the temperature rapidly. After rapid cooling, the water near the surface of the tank warms faster than the water near the bottom, creating a depth-dependent sound speed gradient. Eight hours after adding 380 pounds of pebble ice, the sound speed gradient was 10.7 m/s per meter. The water temperature variability in these tank measurements replicates a portion of the sound speed variability seen in the ocean. This sound speed variability can then be used to test the robustness of machine learning algorithms.