Evolution of Sonobuoy through History & its Applications: A Survey

It's a well known fact that all the oceans and seas together cover more than 70% of the surface of the earth. Thus, exploration of the underwater world has always been the desire & curiosity of the human race. One of the most dramatic event of the twentieth century was destruction and sinking of “RMS Titanic” on April 15, 1912. This shocking incident compelled the desire for a particular device which can foresee hidden objects in the deep seas. In addition, with the advent of u-boats/submarines during both first (1914-1918) and second (1939-1945) world wars, it became even more compelling for scientists and engineers to come up with solutions for detection & neutralization these submerged threats. During early 1940's, a kind of sonar was developed which was deployable from ships and later from aircrafts as well. This special type of sonar was called sonobuoy, a portmanteau for “sonar” and “buoy”. This sonobuoy was capable of being deployed from blimps/aircrafts/helicopters/surface ships/submarines. Earliest sonobuoy deployed from a K-5 blimp detected sounds generated by the S-20 submarine being employed for experimentation. The submarine was detected up to a distance of 3-miles and radio transmission to blimp was in the range of 5 miles. Usually, for passive detection, a sonobuoy detects submarines by acquiring their propeller and machinery noise. In case of active detection, it detects by emitting a sonar “ping”, and then receives the reflections. For special-purpose sonobuoys, the detections are of and magnetic anomalies and electrical fields. In addition, they measure various environmental parameters just as water temperature along the depth, barometric pressure, and height of ocean waves. Generally, sonobuoys are deployed from aircrafts equipped with launchers for their deployment. In addition, these aircrafts have electronic equipment for the reception and subsequent processing of data transmitted by the sonobuoys. One of the challenges to detect submerged vessels is the harsh environment of the sea. The salinity and temperature variations in layers under the sea have profound effects on propagation of sound waves. Exploiting the effects of sea layers as we go deep in the ocean therefore, need a lot of exploring. At present, sonobuoy is the main source which is cheap and easily deployable from aircrafts, ships, or submarines to be employed for this particular purpose. Multidimensional research for multifarious applications/uses of sonobuoys has continued for over a period of last 08 decades. These efforts have resulted in the evolution of sonobuoy in its present form. With the passage of time, the sonobuoy started being employed in various commercial activities along with the Antisubmarine Warfare (ASW) operations within military. This particular study is structured to first introduce the underwater sound propagation, then goes on to discuss the historical perspective of sonobuoys for both during and post World War II eras. The study then goes on to discuss various types and their deployment patterns. Finally, the multifarious uses of sonobuoys are investigated from ASW to fish tracking, from coastal surveillance to environmental research, from earthquake monitoring to search & rescue operations of crashed aircrafts in sea, and so on.