Difference between revisions of "Talk:Global Positioning System"
(Created page with '== Corrected Misleading Statement == At the moment, the article states: '''''Global Positioning System''' ('''GPS''') is a United States satellite system that lets those...')
Revision as of 17:18, 13 January 2010
Corrected Misleading Statement
At the moment, the article states: Global Positioning System (GPS) is a United States satellite system that lets those on the ground, on the water or in the air determine their position with extreme accuracy based on timing signals sent from satellites.
That's not wrong, but the previous version contained more information:
Global Positioning System (GPS) is a United States satellite system that lets those on the ground, on the water or in the air determine their position with extreme accuracy using GPS receivers. These receivers rely on precisely timing signals sent from GPS satellites, with corrections for atmospheric attenuation and relativistic effects.
That there are corrections for relativistic effects can be read in the official specification for the GPS project, i.e., the Global Positioning System Standard Positioning Service Signal Specification, 2nd edition, June 1995:
p. 13: To compensate for relativistic effects, the output frequency of the satellite's frequency standard -- as it would appear to an observer located at the satellite -- is 10.23 MHz offset by a Df/f = -4.4647 x 10-18 or a Df = -4.567 x 10-3 Hz.
p. 39: The coefficients transmitted in subframe 1 describe the offset apparent to the control segment two-frequency receivers for the interval of time in which the parameters are transmitted. This estimated correction accounts for the deterministic satellite clock error characteristics of bias, drift and aging, as well as for the satellite implementation characteristics of group delay bias and mean differential group delay. Since these coefficients do not include corrections for relativistic effects, the user's equipment must determine the requisite relativistic correction. Accordingly, the offset given below includes a term to perform this function.
So, the previous version was correct, and I'll revert to it.
FrankC aka ComedyFan 17:18, 13 January 2010 (EST)