What is a sound velocity profile?

Before the physics was known to use sound waves as a tool for measuring water depths, the practice was to take soundings with lead weights attached to ropes marked with depths. This process was very time consuming and since it was completely mathematical, the error and uncertainty was not easy to calculate. Thankfully, being able to obtain an accurate sound velocity profile is possible because of Physics!

A sound velocity profile is a graphical representation of the sound speed versus depth. An accurate sound velocity profle of the water column is important when using underwater acoustics to explore the unkonwn depths of the ocean. Underwater acoustics is the study of propogation of sound in water where propogation is defined to be the movement of a wave through a medium. So the sound velocity of water is the speed of the propogation of a sound wave through water. The sound velocity is the measurement of the direction and speed of sound rays as they move through the water column. The speed of sound in seawater is most affected by the following three factors:

Water temperature

Salinity of the water

Water pressure.

The sound velocity of water is measured using sonar with special equipment called sound velocity probes. A sound velocity probe measures these three factors along with the dpeth of the probe and calculates an accurate sound velocity based on depth.

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  Sound Velocity Profile

  A sound speed versus time graph. Notice that the minimum speed is at 1000 meters. Photo copyright University of Rhode Island.