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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 60 



DEPARTURE AND DESTINATION ARE KNOWN IN EARTH COORDINATES (LATITUDE AND LONGITUDE). DESIRED TRACK IS ESTABLISHED FROM 

 KNOWLEDGE OF DEPARTURE AND DESTINATION IN EARTH COORDINATES. 



ACTUAL POSITION OF SHIP CAN BE DETERMINED BY MEANS OF LORAN. LORAN IS A HYPERBOLIC NAVIGATION SYSTEM IN WHICH THE NAVI- 

 GATING CRAFT RECEIVES SYNCHRONIZED PULSE SIGNALS FROM AT LEAST THREE KNOWN POINTS. TIME DIFFERENCE BETWEEN ARRIVAL 

 OF SIGNALS FROM ANY PAIR OF THESE TRANSMITTING STATIONS IS MEASURED AND DEI ERMINES A HYPERBOLA-SHAPED LINE OF POSITION 

 ON A LOKAN CHART. BY MEANS OF ANOTHER PAIR OF STATIONS A SECOND SET OF SIGNALS CAN BE USED TO DETERMINE A SECOND LINE 

 OF POSITION. THE CROSSING OF THE TWO LINES OF POSITION GIVES A POSITION FIX IN LORAN COORDINATES. • 



LORAN CHART SHOWS LORAN LINES OF POSITION SUPERIMPOSED ON GEOGRAPHIC PLOT. THEREFORE, LOCATION OF PRESENT POSITION IN 

 LORAN COORDINATES GIVES DIRECTLY THE LOCATION IN EARTH COORDINATES. 



Figure 4. — Navigation by means of loran. 



principles of loran, and similar radio-navigation systems, in ■wliicli the 

 navigating vehicle receives synchronized pulse signals from at least 

 three transmitting stations (fig. 4). The time difference between the 

 signals received from any two stations determines a hyperbola-shaped 

 line of position on the navigation chart. Use of at least one other 

 transmitting station determines a second such line of position. The 

 crossing of these two lines of position on the navigation chart estab- 

 lishes a highly accurate fix. With this navigation technique, the dif- 

 ficulties that beset visual observations of landmarks are substantially 

 eliminated. Navigation by such radio-navigation nets, which cover 

 wide areas of the earth's surface, is very useful for locating stationary 

 points and slow-moving vehicles, but is not well adapted to situations 

 that involve rapid maneuvers of fast vehicles. 



Radar, which uses wavelengths shorter than those of the radio- 

 navigation systems just described but longer than tliose of light, gives 

 direct indication of distance from a single landmark. It is an ex- 

 cellent means for navigation by direct-line-of -sight contacts, with the 

 restrictions associated with light substantially eliminated (fig. 5). 

 The landmarks for radar may be ordinary terrain features and arti- 

 ficial objects, such as lighthouses, buoys, or other vehicles. Radar 

 devices usually operate by comparing transmitted and reflected 

 pulses. The time between sending and receiving for a particular pulse 

 gives the distance to the reflecting surface in terms of the velocity of 

 liffht. 



