loran (redirected from Group Repetition Interval)

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.

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loran

 abbreviation of long-range navigation

A land-based system of radio navigation in common use over the continental United States and in its coastal waters. It was developed during World War II for the U.S. military. A civilian version, Loran-C, was developed in the 1950s. Loran-C can be used to determine position within about 30 ft (10 m) by comparing signals from multiple stations. Loran-like systems operate in many coastal waters around the world. However, the availability of the global positioning system (GPS), with a typical accuracy of 3 ft (1 m), has begun to relegate loran to backup status.