Sonobuoy

The sonobuoy, sometimes called sonobuoy is a special buoy with hydrophones ( underwater microphones ) is equipped to detect submarines or other sound sources underwater. They are mostly used by maritime patrol aircraft for anti-submarine detection. For this task, they are dropped from the aircraft; by the impact of the hydrophone is released and drops to a wire to a predetermined depth. A piece of wire is carried off by a stretchable rubber band, thereby decoupling the movements of the hydrophone is accessed from the sea. The signal received from the buoy signal is sent to the aircraft in the VHF range. They are usually equipped with a sealed by a salt tablet flood hole, so that they sink after a predetermined period of several hours when the tablet is dissolved.

The data transmitted from the buoys are evaluated on the plane with special analysis equipment. The sounds are subjected to, for example, a frequency analysis. And the other from the observed spectral characteristics of the noise is closed to the source. If the observed noise with reasonable probability is classified as a submarine, an attempt is made in specific geometric arrangements to close by the dropping of multiple sonobuoys on the position of the submarine. Because they only listen, distances to a target can be detected only indirectly. One uses the volume of the target and sets in relation to the distance from the hydrophone (according to = close, quietly = remote). With several buoys can be as the approximate position and after prolonged observation and course and speed of the target can be determined. The commonly used today DIFAR buoys provide in addition a bearing of the target.

Sonobuoys were used during the cold war for maritime reconnaissance from the air in particular by the U.S. Navy in quantities of several 100,000 per year.

Special forms of sonobuoy

In addition to the described standard buoys, there are also more expensive specialty types: DIFAR buoys (Directional Frequency Analysis and Recording), which, through sound pressure gradient formation or by a horizontal array of hydrophones, a horizontal direction determination. The VLAD buoys (Vertical Line Array Directional ) buoys beyond to solve vertically.

Active sonobuoy work as an active sonar system and deliver next distance and bearing to a target. Today consistently are DICASS (Directional Command Activated Sonobuoy ) or CAMBS ( Command Avtivated Multibeam Sonobuoy ).

For the measurement of environmental parameters BT ( Bathythermographic ) buoys are used to measure the background noise ( ambient noise ) and the temperature stratification.

Occasionally the AXBTs ( Airborne Expendable Bathythermograph ) are counted among the sonobuoy, because they are used by the same ejector device on the aircraft and therefore the sonobuoy look similar. With them, the sound velocity profile is measured in the water.

Some helicopters use sonobuoys as a complement to sonar systems that are lowered with a winch on the cable into the water and then inserted again. This normally results in an active sonar is used. Helicopters generate directly below them disturbing noise in the water, which considerably complicates the passive tracking.

On ships special seawater-resistant sonar buoys in accordance with SAE AS 8045 are used. The sonar buoys are attached to Privacy capsules ( Voyage Data Recorder VDR / S -VDR ) and have the task, in the case of activation ( immersion in water) for at least 30 days a locating signal in the range 25-50 kHz (DIN EN 61996, Maritime ), with a sound pressure level of 160.5 dB, leave.