The Decca Navigator phase measurement system can provide 2-4 mile 

 positional information at maximum ranges of 200-500 nautical miles but is gen- 

 erally limited to ranges of the order of 250 nautical miles for the highest ac- 

 curacy on a 24-hour/day basis. Coverage is available throughout Europe and 

 the British Commonwealth. The Navy's developmental Omega system promises 

 positional accuracies of 0.5-1 nautical mile for ranges as great as 5000 nautical 

 miles . This system will probably use three frequencies to fix a course and a 

 fine position. World-wide coverage by 8-10 ground stations is promised and 

 could be available by the late 1960's or early 1970's. 



World-wide coverage by a system of satellites and ground stations is 

 also expected. The Navy's passive Transit program requires a minimum of 

 four satellites in polar orbit and should yield positional information to better 

 than ± 0.1 nautical mile. Several less sophisticated systems using larger num- 

 bers of satellites are currently being studied by other Governmental agencies 

 for use by commercial and scientific groups . One system under consideration 

 is the precision satellite tracking system, known as Secor, now in operation for 

 the Army Map Service . It has demonstrated a positioning capability to geodetic 

 accuracies of a few meters with base-line lengths greater than 2000 mUes . 

 Less sophisticated equipment of this type would be capable of positioning ac- 

 curacies of 0.25-1 nautical mile when used for ship and aircraft navigation. 



The inertial navigation systems in use by the Navy are passive, self- 

 contained, and not directly subject to enemy action. Although these systems 

 are highly sophisticated, they still accumulate a small error over a period of 

 time and require recalibration, using an external source. The first commer- 

 cially available inertial equipment is much less sophisticated. It will initially 

 be used aboard high-speed, long-range, commercial aircraft and will generate 

 an average error of less than two miles per hour of travel. 



Acoustic Doppler navigation systems are not yet fully developed to 

 the point where they can be used effectively in waters greater than a few hundred 

 feet deep. These systems should help improve present dead -reckoning proce- 

 dures and also appear to be attractive for use in shallow waters or aboard deep 

 submersibles operating near the ocean floor. Navigation accuracies available 

 with these systems are of the order of 1% of velocity and 1% of distance. 



B, MID -RANGE NAVIGATION SYSTEMS 



Mid-range navigation systems (Table II- 2) are defined here as having 

 ranging capabilities up to about 400 nautical miles. These systems are generally 

 most useful for ship -positioning and survey applications where high accuracy 

 and reproducibility are required. Because mid-range frequencies are used, 

 the range and accuracy of these systems will be limited during evening hours 



artbur ai.HittlcJnr. 



