Acoustic homing

Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target.

By listening to the sound it made when it hit the seafloor, they were able to estimate the water's depth and the nature of the seabed.

In the 18th century, foghorns[2] were developed to aid navigation for ships in low visibility conditions caused by fog.

In the early 19th century, scientists and inventors such as Charles Babbage[3] and Samuel Morse[4] experimented with underwater signaling systems.

In the early 20th century, a Canadian inventor Reginald Fessenden[5] developed what many believe to be the first practical underwater acoustic communication system.

Sonobuoys were small floating devices dropped by aircraft which detected underwater sounds and transmitted information back to the sender.

The system actively transmits sound waves and receives echoes from the target which it then processed.

Sensing method: Active acoustic homing systems use transducers or hydrophones which function as both sound transmitters and receivers.

Limitations: Active acoustic signals can be detected by the target, potentially giving away the position of the homing system.

Uses: Active acoustic homing is commonly used in anti-submarine warfare, where it is used to locate and engage submarines by pinging them with sound signals.

Sensing method: Passive acoustic homing systems use hydrophones or microphones to detect and analyze sounds emitted from the target.

Some examples of these distress signals include emergency beacons and devices carried by people stranded at sea or in remote areas.