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Long Range Navigation(LORAN)

Research Paper

Long Range Navigation (LORAN) is a land-based navigationalsystem developed by the U.S for the purposes of providing anavigation system that covers large distances. LORAN uses theconic section the hyperbola to determine the position of thereceiver via the transmission of pulse radio waves from aminimum of three ground-based stations based on the timedifference between the pulses. This allows for the precisedetermination of the time difference between signals fromground stations within a range of 1000 nautical mile radius (W.

J. Ecker, 2012).

The main application of LORAN-C is navigation. It is a reliablesource of both aerial and nautical navigation since it isunaffected by weather conditions and has a large area ofcoverage, which makes it particularly advantageous in remotelocations. It can also be used as a system for synchronizing

long range time distribution, determining the location ofthunderstorms and nuclear detonations, researchingastronomical phenomena, location and navigation of vehiclesin space and wave propagation studies are some uses amongmany others (Bailey & Jansky, 1962). LORAN is also importantin establishing a precise reference frame for time, and is usedextensively for this reason by telecommunication companies,power companies and the like (W. J. Ecker, 2012). This reportfocuses on the use of LORAN as a hyperbolic land-basednavigation system.

The U.S. National Defense Research Committee wascommissioned to create a long-range navigation system ofhigh precision in 1940 for aircraft navigation. They usedsynchronized pulses of radio waves from ground-basedtransmitting stations. In 1942, the first practical navigationalsystem based on hyperbolic radio transmissions wasimplemented in England. This system was call GEE, and it wasin frequent use by the Air Forces of the Allies in World War II.Radio pulses were transmitted periodically by ground stations,

which were intercepted by receiving units in the air (Bailey &Janskey, 1962).

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After multiple accuracy tests and field trials, GEE evolved intoa new program, called LORAN-A (LOng RAnge Navagation-A),which became fully operational under the responsibility of theU.S Coast Guard and the Royal Canadian Navy in 1943 to beused in marine navigation (W.J. Ecker, 2012). The expediencyof LORAN resulted in the creation and installment of severalvariations of the program during World War II, the mostsuccessful called Skywave Synchoronized LORAN (SS LORAN).

The single successor of these adaptations of LORAN still in usetoday is LORAN-C, which has been used by over 48 continentalstates in a period of over 52 years, although the use of LORANis in steep decline as a result of the introduction of satellitenavigation systems, such as the Global Positioning System

(GPS).

LORAN uses a minimum of 3 stations, one of which is called themaster station and the rest are called slave stations. Eachslave station forms a pair with the master station and theybecome the foci of the hyperbolas formed between them. Thedefinition of a hyperbola formed by a pair of stations is thelocus of points such that the difference in time of arrival of thesignals from the master and slave stations is a constant. Thislocus is called a LOP (Line of Position) and is a reference for

latitude and longitude. Since the receiver could be anywhereon this locus, the second pair of stations is needed to find anintersection which would indicate the actual location of theLORAN receiver. All that the receiver needs to do to work outhis location is find the corresponding LOPs on a LORAN chart,which is a map with the LOPs superimposed, and find wherethey intersect. The intersection of the lines will determine thelatitude and longitude of the receiver (W.J. Ecker, 2012).

The use of periodic pulses of radio emissions is what separates

LORAN from other hyperbolic radio navigation systems. Themaster station sends groups of signals out consisting of 8pulses in 1000 microsecond intervals and a 9th pulse with a2000 microsecond interval whereas the slave stations onlysend out 8 pulses with a 1000 microsecond interval. Themaster station sends out the first group of signals which arereceived by the receiver and the slave station. When the slavestation receives the signal from the master station, a period oftime will have elapsed called the emission delay, and the slavestation will wait a short period of time, termed the coding

delay before sending its own group of pulses out. Thedifference in time of arrival between the signals is then the

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absolute value of the time of arrival of the slave signal, whichconsists of the emission delay plus the coding delay, minus thetime of arrival of the master signal. The receiver uses thisdifference in pulse pattern to determine which signal belongsto which station and from that, calculates the Time Difference(W.J. Ecker, 2012).

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Bibliography

Bailey & Jansky, 1962. The LORAN-C system of navigation(report prepared for the U.S. Coast Guard). A-Division of

Atlantic Research Corporation, Washington, D.C.

Encyclopedia Britannica, 2013. LORAN. Accessed online: 16March 2013.< http://www.britannica.com/EBchecked/topic/347964/loran>

U.S. Coast Guard Navigation Center, 2012. LORAN-C generalinformation. Accessed online: 16 March 2013.< http://www.navcen.uscg.gov/?pageName=loranMain>

W.J. Ecker, 2012. The LORAN-C user handbook(CommandmentPublication P1652.5). Accessed online: 16 March 2013.< http://www.navcen.uscg.gov/?pageName=loranHandBook>