LORAN(redirected from GRI (LORAN))
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loran(lôr`ăn'), long-range, accurate radio navigational system used by a ship or aircraft to confirm or to determine its geographical position. The term loran is derived from the words long-range navigaton. Loran, operating in the 1,700-kHz range, measures the time-of-arrival difference between two signals transmitted from two geographically separated ground stations. The pulse from the first station, called the master, triggers the second station, called the slave, into transmitting a similar pulse after a set time delay. Knowing the elapsed time difference, the navigator refers to a loran chart and selects his line of position. The chart contains groups of hyperbolic curves of constant time differences between particular station pairs. The position of the receiver (ship or airplane) will be somewhere along the curve that corresponds to the measured time difference. By taking a similar time-difference reading from a second pair of stations whose curves intersect those of the first pair, a definite geographic fix may be obtained.
The designation of a family of radio navigation systems by which hyperbolic lines of position are determined by measuring the difference in the times of reception of synchronized pulse signals from two or more fixed transmitters. Derived from long-range navigation.
LORAN (long-range navigation)
LORAN(LOng RAnge Navigation) A ground-based navigation system developed by the U.S. government during World War II. Modeled after the British GEE system, LORAN receivers pinpoint their location by triangulation with three LORAN transmitters, approximately 75 of which are located throughout the world. With 29 ground stations covering all of North America, LORAN's long-range signals provide an economical navigation system, although less precise than GPS with its correction systems (see GPS and GPS augmentation system).
LORAN-C is the surviving LORAN technology. Developed with great haste during World War II, LORAN-A was still used during the Vietnam war for aircraft navigation. LORAN-B was an improved version, which was abandoned in favor of LORAN-C. LORAN-D modified LORAN-C for short-range use, and LORAN-F was an alternate name for a Motorola navigation system for unmanned drones.
After China shot down its own communications satellite in 2007, there was renewed interest in LORAN as backup to the satellite-based GPS system, should it ever be compromised. eLORAN (an Enhanced LORAN) uses more advanced receivers and transmission modes, which improves LORAN accuracy to eight meters. eLORAN receivers accept all signals within range as well as a new set of correction signals.