What major factor negatively affects sound propagation in water when using an Acoustic Position Reference system?

When considering the major factors that negatively affect sound propagation in water, thruster activity is a significant element in the context of an Acoustic Position Reference system. Thrusters generate noise and turbulence in the water, which can interfere with the acoustic signals used for positioning. This noise can mask the return signals from the acoustic transducers, making it harder for the system to accurately determine its position. The increased turbulence caused by thruster operation can also lead to scattering and attenuation of the sound waves propagating through the water.

While wave action, temperature gradients, and water salinity can impact sound propagation as well, they typically do so in more predictable and controlled manners that may be mitigated or accounted for in various operational scenarios. For example, temperature gradients can affect sound speed but usually lead to refractive effects rather than complete interference. Water salinity influences sound speed but is relatively stable in a given operational area. Thus, while these factors are important, the disruptive impact of thruster activity during operations stands out in the context of acoustic positioning systems.