What device is specifically designed for detecting underwater sounds?

The device designed specifically for detecting underwater sounds is the hydrophone. A hydrophone is an underwater microphone that converts underwater acoustic signals into electrical signals, allowing for the detection and analysis of sounds beneath the surface of water. This makes it particularly useful for various applications such as marine biology, underwater exploration, and naval operations.

Sonobuoys, while also used in underwater sound detection, are specialized buoys that can be deployed from aircraft or ships to detect submarine activity. They carry hydrophones but also include additional technology to enhance their functionality, such as signal processing capabilities. The main emphasis of a sonobuoy is on its ability to transmit data to surface vessels or aircraft, rather than solely for sound detection.

Passive sonar, on the other hand, refers to the technology that listens to sounds in the ocean without emitting its own signals. It often utilizes hydrophones but is a broader term that encompasses various systems and devices that operate in this manner.

Echo sounders are used for measuring water depth by emitting sound waves and analyzing their return. They do not specifically focus on detecting sounds made by creatures or objects in the water but rather on navigation and mapping.

Therefore, the hydrophone is the most direct answer to the question, as it is specifically designed to detect sounds