164 • Marine Minerals: Exploring Our New Ocean Frontier 



stance), is accurate to 16 meters or better. GPS ac- 

 curacy to within 10 meters is considered routine. 

 The less precise Standard Positioning Service is pri- 

 marily for civilian use and is accurate to within 

 about 100 meters. (Use of GPS, as well as LORAN- 

 C and other systems in the differential mode — in 

 which a ground receiver at a known location is used 

 to check signals and measure range errors, allows 

 higher accuracies to be achieved but takes much 



longer). NOS uses GPS when it can to calibrate 

 the other systems it uses (Raydist and ARGO). 

 GPS is currently available about 4 hours a day; 

 however, it is impractical to go to sea for just the 

 short period in which the "window" is open. Con- 

 sequently, in the near term, NOS is focusing its 

 survey work on the inner half of the EEZ where 

 Raydist and ARGO can be used. 



