New Data from
U.S. National Geodetic Survey
Comparison of Positions With and Without Selective Availability
                                         May 1, 2000                                                                 May 2, 2000

The images compare the accuracy of GPS with and without selective availability (SA). Each plot shows the positional scatter of 6.5 hours of data (0730 to 1400 UTC) taken at one of the Continuously Operating Reference Stations (CORS) operated by the U.S. Coast Guard at Hartsville, Tennessee. On May 2, 2000, SA was no longer present. The plots show that SA causes 95% of the points to fall within a radius of 44.2m. Without SA, 95% of the points fall within a radius of 4.1m.

Fine Print: Data taken at the Hartsville National CORS station, National Geodetic Survey, NOAA. Data with SA were taken from 0730 to 1400 UTC on May 1, 2000. Data without SA were taken from 0730 to 1400 UTC on May 2, 2000.
Both data sets were taken at 30 second intervals. Instrumentation was an Ashtech Z-12 receiver. GPS data were dual-frequency pseudorange (both L1 and L2) incorporating ionospheric correction. Data were processed in accordance with the GPS Interface Control Document ICD-GPS-200C, using the broadcast orbit parameters in the World Geodetic System WGS 84 (G873) reference system.

Jack Yeazel