A second method of radar navigation and ship positioning requires the 

 use of transponders (as in Shoran) and reflectors positioned at known geograph- 

 ical points . Standard methods of triangulation are then used. 



Dead reckoning is an essential factor in positioning vessels by the use 

 of radar, just as it is in conventional navigation. 



3. ACCURACY 



The accuracy of radar navigation is principally determined by the 

 characteristics of the radar set and the interpretation of its display. Navigational 

 aids in the form of either transponders or reflectors enhance the return signal, 

 making possible better signal match and interpretation. Range accuracies of 1 

 part in 2500 or better can be measured with modern radar equipment at ranges 

 out to about 50, 000 yards. Decreasing accuracy can be expected at ranges 

 greater than 50, 000 yards . A range precision of ± 80 ft for 99 .7% of the meas- 

 urements out to the maximum range of the parent radar equipment is practical 

 when a precision range unit is used.'"^' Angular resolution of 1° can be expected 

 with most equipment if the PPI is accurately centered, parallax is avoided, and 

 the receiver gain is adjusted to give the narrowest bearing line . 



Ranges of 10-15 miles can be expected with both 3 and 10 cm marine 

 radar under most conditions of use. Higher power levels and antenna height 

 can extend these surface ranges to 50 miles or more with some military equip- 

 ment. 



REFERENCES 



1. Radar Technique - Radio Aids to Navigation S.P. 39, Ch. 5, International 

 Hydrographic Bureau, Monaco. 



2. L. N. Ridenour, Radar Systems Engineering, M.I.T. Radiation Laboratory 

 Series, Vol. I, McGraw-Hill Book Co., 1947. 



3. See Alpine Precision Navigation System Model 430, pp. 138-142. 



137 



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