Which factor has the most effect on sound velocity down to 1,000 feet?

The most significant factor affecting sound velocity down to 1,000 feet is temperature. In seawater and other fluids, the speed of sound is influenced primarily by its temperature due to the relationship between temperature and the motion of molecules. As temperature increases, the kinetic energy of the molecules also increases, allowing sound waves to travel faster through the medium.

At depths less than 1,000 feet, the temperature gradient in the ocean plays a crucial role in determining sound speed. Warmer water has a higher velocity of sound because the increased molecular activity facilitates quicker transmission of the sound waves. This effect becomes more pronounced in warmer regions of the ocean compared to colder ones.

While factors such as humidity, altitude, and wind speed can influence sound propagation, their effects are generally less significant than that of temperature, particularly in the context of underwater acoustics at shallow depths. Humidity primarily affects sound in the air, while altitude is more relevant to atmospheric conditions rather than underwater. Wind speed can create surface currents that might affect sound transmission, but again, this influence is secondary to the direct impact of temperature on sound velocity.