For the Secor-type system the distance from each ground station to 

 the satellite is determined by phase comparison techniques. The master station 

 transmits frequency- modulated cw signals in bursts which are repeated by the 

 satellite transponder and transponded again by each of the other stations. Speed 

 and course information from the navigating vessel would also be transmitted to 

 the master station via the satellite. The resulting signals would be received 

 back at the master station, where phase comparison measurements would be 

 made and the satellite-to-ground ranges r , r , r , and r computed. 



To obtain information to calculate the range error caused by iono- 

 spheric refraction, the satellite retransmits phase information on two or more 

 frequencies . With this information and the range and speed information the 

 coordinates of the navigating vessel would be computed at the master station 

 and transmitted via the satellite to the vessel. 



So far the most sophisticated form of Secor has achieved geodetic 

 positioning accuracies of better than 10 ppm.'^' For navigational requirements 

 and accuracies of 0. 1-0.25 nautical mile less sophisticated equipment would 

 be required. 



REFERENCES 



1. R. B. Kershner and R. R. Newton, "The Transit System," J. Inst, of Navi - 

 gation, April 1962. 



2. W. H. Grier and G. C. Weiffenbach, "A Satellite Doppler Navigation 

 System," Proc. IRE, April 1960, p. 507. 



3. Radio Doppler Method of Using Satellites for Geodesy, Navigation and 

 Geophysics Within the Planetary System, Johns Hopkins University Applied 

 Physics Laboratory, Report RG-385, January 1961. 



4. Study and Analysis of Selected Long-Distance Navigation Techniques , Vol. II, 

 Final Report, Inst, of Science and Technology, University of Michigan, 

 March 1963. 



5. E. S. Keats, "Ship Navigation with Satellites, " Westinghouse Engineer , 

 January 1963. 



6. J. H. Reid, The Secor Approach to Coordinate Determination for Ships and 

 Aircraft , Technical Paper No. 1, Cubic Corp., San Diego, Calif., 4 June 1964. 



7. Brig. Gen. T. S. Hayes, Secor for Satellite Geodesy, Tenth International 

 Congress of Photogrammetry, Lisbon, Portugal, September 1964. 



94 



Arthur Zn.^ittlfjnr. 



