Fisherman's Radar

As sound waves get shorter, their note rises in pitch. When the note is too high to be heard by human ears, its waves are called "supersonic."* Inaudible though they are, such vibrations have their uses.

The Bendix Corp. is exhibiting a device called "the fisherman's radar." From a ship's bottom, a supersonic wave strikes down to the bottom of the sea. The time it takes to be reflected back, measured electronically, gives the depth of the water, which is recorded continuously on a moving strip of paper.

The instrument can help locate fishy ledges. A trawler dragging a net along the bottom can swerve to dodge a rock which might cause costly damage. The character of the reflected wave distinguishes a soft from a rocky bottom, which is something a fisherman likes to know. Occasionally, fish themselves show up as objects above the bottom. Bendix does not claim that the idea is new. But its instrument is remarkable because it is cheap and simple--and thus within reach of well-heeled commercial fishermen.

*Not to be confused with "supersonic speed," i.e., speed above that of sound.

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