Directional Hydrophone Records Whale Voices

"Trident" is probably the first research vessel in this country to have installed a directional hydrophone for listening to undersea sounds.

On two recent trips the instrument has proved its value in studying the sounds made by whales. The directional hydrophone eliminates back and side noises and makes it possible to determine the exact compass point from which sound is coming.

The research on whale sounds is one aspect of a study of sounds of biological origin that has been underway for a number of years directed by Marie- P. Fish of the URI marine laboratory and supported by the Office of Naval Research.

The hydrophone was installed in the bottom of the ship about a third of the way back from the bow while the ship was in drydock last winter. A standard submarine directional hydrophone is mounted on a steel shaft taken from a submarine periscope.

The hydrophone is up against the hull when the ship is moving and is lowered hydraulically four feet below the hull when it is in use.

The shaft extends through the, hull and up into the main labora tory of the ship where the electronic equipment that amplifies and records the sound is located. The direction and raising and lowering of the hydrophone is also controlled from the laboratory.

Once the direction from which the sound is coming is determined, the ship can close in on the marine animal making the noise.

In addition to the new directional hydrophone, "Trident" has another hydrophone attached to, the bow which is stationary and picks up sound from any direction.

When the ship is on a cruise, a whale watch is kept from the deck and the omnidirectional hydrophone can be used to pick up any sounds in the surrounding water. The tracking of the whale requires a combination of sound and sight and an intercom connects the laboratory with the watch. When a whale is sighted or heard, the ship slows down, the directional hydrophone is lowered, and the ship progresses in the direction of sound and sight until the whale can be identified and the sound recorded. During the recording all excess sound on the ship is reduced or cut off.

It is possible to see a whale for about three miles, and the distance they can be heard clearly is about one mile, although this is dependent on the calmness of the ocean and other conditions.

Since the installation of the new hydrophone Mrs. Fish and her assisiants have monitored and recorded three large schools of sperm whale, as well as humpback whale, minke whale, finbacks and porpoise.

The whales generally surface four to seven times in succession and spout and then dive deeply and remain submerged for some time. Except when it is at the surface the whale is audible. The sounds it makes differ with the situation and the species so that an entire whale "vocabularly" must be studied. Mrs. Fish's work attempts not only to identify the whale, but to determine the meaning of the various whale ''comments."

At the University the tape recordings are studied and vibralyzergrams (pictures of the frequency and pattern of sounds) are made for the various species. Hundreds of these are on file for each species and of whale. Over the years Mrs. Fish has assembled a file on many of the no less than 110 species of whale.

The gear has also been used for tracking Swallow floats (submerged aluminum floats that move with the current), and made it possible to hear them over longer distances than ever before.

The key man in operating and designing the equipment is a former Navy chief sonarman, Paul J. Perkins, who retired two years ago after 20 years in the Navy. He learned all the Navy could teach him about underwater sound at Navy sonar schools, at the electronic laboratory at San Diego and on submarine duty. During World War 11 he was on sub chasers, submarines and a seagoing tug operating sound gear detecting, identifying and tracking submarines, ships and biological sound sources.

Aside from the scientific values of this sound research, Mr. Perkins knows from experience the -importance of the Navy being able to identify unusual underwater sounds made by animals in the sea. Repeatedly, while he was on submarine duty, he heard the same loud unidentifiable, noise. When the submarine attempted to lose the sound it continued to follow the ship. When they finally surfaced it turned out to be not an enemy ship but a curious whale whose voice at that time had not been identified.

Mr. Perkins also explains that the directional hydrophone can be used as a substitute for radar bearing detection if for any reason the ship's radar is not functioning.

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