Abstract
Selective Availability (SA) was turned on between the period of March 25 to August 28, 1990. SA is aimed to degrade positioning accuracy of civilian GPS users by adding intentional errors into the broadcast ephemerides and satellite clocks in the GPS navigation message, and it is believed to be implemented in the full operational phase of GPS (about mid-1993).
In order to estimate the magnitude, time behavior, dynamical and statistical characteristics of SA errors, the pseudorange and delta-pseudorange observations were taken during the above period using a C/A code, single channel GPS receiver NAVCORE-1 of National Aerospace Laboratory (NAL). And SA errors were analyzed by computing residuals for both pseudorange and delta-pseudorange data.
Analysis results show that: (1) SA was implemented on the Block-II satellites only. (2) SA errors in the pseudorange data consisted of both short periodic components with the period of a few minutes and long periodic terms with the period of a few hours, the magnitude ranging from 30-50m (RMS), which is consistent with the stated policy of U. S. Department of Defense (DoD). (3) For the Block-II satellites the anomalous residuals in the delta-pseudorange data were also observed, but the magnitudes of which were below the formal standard deviation of the receiver error and thus the effect on navigation accuracy in velocity can be ignored.
