Which factor is essential for determining the effective transmission of sound waves underwater?

The effective transmission of sound waves underwater is significantly influenced by the bottom composition, which is why this choice is correct. The characteristics of the seafloor, including its type and structure, can affect how sound waves reflect, refract, or are absorbed as they travel through water. For example, hard substrates like rock will reflect sound waves differently compared to softer materials like mud or sand, leading to variations in acoustic behavior.

The bottom composition plays a critical role in sonar operations and underwater acoustics, impacting the detection and navigation capabilities of submarines and other underwater vehicles. This is essential for understanding how sound interacts with the environment, which in turn affects communication and sensing technologies used in oceanography and marine operations.

While other factors such as water temperature, water depth, and salinity also play a role in sound transmission, they primarily influence the propagation speed and attenuation of sound in the water column, rather than the interaction at the seabed level, which is directly affected by bottom composition.