Hyperbolic navigation

Hyperbolic navigation refers to a class of navigation systems based on the difference in timing between the reception of two signals, without reference to a common clock. This timing reveals the difference in distance from the receiver to the two stations. Plotting all of the potential locations of the receiver for the measured delay produces a series of hyperbolic lines on a chart. Taking two such measurements and looking for the intersections of the hyperbolic lines reveals the receiver's location to be in one of two locations. Any other form of navigation information can be used to eliminate this ambiguity and determine a fix.

The earliest known hyperbolic system was used during World War I as an acoustic location system for locating enemy artillery. The sound of a shell being fired was received by several microphones, and the time of reception sent to a computing center to plot the location. These systems were used well into World War II. By that time, however, radio techniques were becoming much more capable, and most hyperbolic systems are based on radio means.

The first such system to be used was the World War II-era Gee, introduced by the Royal Air Force for use by RAF Bomber Command. This was followed by the Decca Navigator System in 1944 by the Royal Navy, along with LORAN by the US Navy for long-range navigation at sea. Post war examples including the well-known US Coast Guard LORAN-C, the international Omega system, and the Soviet Alpha and CHAYKA. All of these systems saw use until their wholesale replacement by satellite navigation systems like the Global Positioning System (GPS).

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