I. INTRODUCTION 



Familiarity with navigation and ship -positioning problems is a pre- 

 requisite for personnel concerned with ASW systems . Historically, celestial 

 techniques and dead -reckoning methods have been used for marine navigation. 

 During the past 20 years, however, various navigational aids and positional sys- 

 tems which permit the navigator to fix his position without regard to cloud or 

 weather conditions have become available. Since World War II, but particularly 

 since 1950, the trend in navigation equipment has been toward greater positional 

 accuracy, continuous position -fixing capability, and longer-range operation. 

 These improvements are being achieved by the use of more sophisticated elec- 

 tronic techniques, including celestial methods, electromagnetic and acoustical 

 signals, and inertial systems. Automatic computation and display equipment 

 has further simplified the work of the navigator. The more sophisticated naviga- 

 tion systems allow the computer to complete as many of the routine calculations 

 as possible, thus reducing the time the navigator requires to fix his position ac- 

 curately. Such methods also tend to reduce the incidence of human error. 



The high positional accuracy of a sophisticated navigation system is 

 expensive, and highly trained personnel are required to operate and maintain 

 the equipment. Certain military and most oceanographic research and survey 

 problems require positional accuracies of 0.1 - 0.5 nautical mile or better. 

 This high precision may not be required or economically justified, however, for 

 the vast majority of marine navigation problems, where a vessel is interested 

 only in steaming from one port to another . 



Navigation systems have been improved at the expense of greater 

 equipment complexity, sophistication, variety and cost, compared to older navi - 

 gation methods . System reliability and maintainability remain as problems, and 

 precision coverage in all ocean areas using any one system is not yet available . 

 The prudent marine navigator must use all navigation systems at his disposal 

 and compare their results in order to plot his most probable position at a given 

 point in time. A combination of systems is required to provide cross checking 

 and to satisfy the differing requirements for precision, fix renewal period, and 

 range . 



We have divided marine navigation and ship -positioning systems into 

 three classes: long range, mid range, and short range. The basic capabilities 

 and limitations of the systems in each class are summarized in Section II. The 

 fundamentals of electronic navigation, propagation phenomena, and range and 

 accuracy considerations are discussed in Section III. In Sections IV -VI the 

 important characteristics of the several classes of systems are described. 



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