What are the service levels provided by GPS?
A. GPS provides two levels of service: • a Standard Positioning Service (SPS) for general civil use; and • a Precise Positioning Service (PPS) primarily intended for use by the Department of Defense and U.S. allies. There are no restrictions on SPS usage and is available to users worldwide. With Selective Availability (SA) , SPS provides predictable accuracies of 100m (2drms, 95%) in the horizontal plane and 156m (95%) in the vertical plane. UTC (USNO) time dissemination accuracy is within 340 nanoseconds (95%) referenced to the time kept at the U.S. Naval Observatory. These accuracies reflect the last signal specification in the Federal Radio Navigation Plan which is in the process of being revised to reflect the accuracy obtained following the deactivation of Selective Availability. Without SA, SPS accuracy would be of the order of 25m (2 drms, 95%) in the horizontal plane and 43m (95%) in the vertical plane. PPS provides a predictable accuracy of at least 22m (2drms, 95%) in the hor
