In marine seismic one or an <b>array of airguns</b> is used to produce sound waves by releasing air under a pressure of 200 bar about every minute. The waves are reflected by the various sediment and rock layers in the ground. The echo is recorded by a streamer which is a some hundred to thousand meter long hose, filled with hundreds of hydrophones in oil, towed to the research vessel.
<a href="//commons.wikimedia.org/wiki/User:Hgrobe" title="User:Hgrobe">Hannes Grobe</a>, Alfred Wegener Institute
CC BY-SA 2.5
<span class="int-own-work" lang="en">Own work</span>