INTERACTIVE:
The ship Rude, equipped with a special sonar, searches an area investigators believe may be the site where an emergency beacon emitted a brief signal

July 18, 1999
Web posted at: 8:33 p.m. EDT (0033 GMT)

From Correspondent Ann Kellan

(CNN) -- Searchers looking for the missing plane of John F. Kennedy Jr. have brought in the Rude (pronounced Roo-dee), a research ship operated by the National Oceanic and Atmospheric Administration that is equipped with what's called "side-scan sonar."

The sonar is attached to a device known as a "fish," which is towed by a boat or submarine. The objective is to get a profile of the ocean floor.

The sonar sends out a pulse of sound. When that pulse hits the sea floor, it echoes or reflects back to the surface and is recorded by the equipment, giving searchers a picture of the size and shape of objects.

Because crash debris usually has sharp lines and corners that aren't found in nature, the sonar can tell the difference between the debris and natural features of the ocean floor such as rocks.

Unlike other kinds of sonar that send out pulses in one direction to determine how far away something is, side-scan sonar sweeps out below and to the sides of the ship, giving a much broader picture.

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