Hydroacoustic sensing involves "passive acoustics" (listening for sounds) or active acoustics making a sound and listening for the echo, hence the common name for the device, echo sounder or echosounder. There are a number of different causes of noise from shipping.

What does hydroacoustic search do in world of warships?

Hydroacoustic Research I/II

Increases detection capability of enemy torpedoes and ships.

What is hydrostatic search?

Hydrostatic testing is used to find leaks in pressurized systems. Pipelines, plumbing, boilers, fuel tanks, and gas cylinders are commonly tested with this method. ... A hydrostatic test involves filling a system with a liquid. Once the system is filled with liquid, it's pressurized to test the system's integrity.