Current operations nominal 24 satellite constellation

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Unformatted text preview: tional conditions - NANUs applied over intervals defined by 2 SOPS - Global 2 x 2 degree grid (10,356 locations) - 24 hour sample intervals - One minute sample steps - All-in-view NAVSOL - SPS signal-in-space UREs, with 50 cm of added noise to represent uncertainty due to Tgd - Five degree mask angle - Statistics are result of empirical sorts for each location over the global grid 4 3 2 Worst Site 95% Horizontal Error 1 Global 95% Horizontal Error 0 0 5 10 15 20 25 30 Day of Month (June 2000) Figure A-5-7. Typical Example of GPS SPS SIS Horizontal Performance – June 2000 GPS SPS Global Vertical Performance -- June 2000 12 95% Vertical Error (meters) 11 ANALYSIS CONDITIONS 10 - Analysis conducted under normal constellation operational conditions - NANUs applied over intervals defined by 2 SOPS - Global 2 x 2 degree grid (10,356 locations) - 24 hour sample intervals - One minute sample steps - All-in-view NAVSOL - SPS signal-in-space UREs, with 50 cm of added noise to represent uncertainty due to Tgd - Five degree mask angle - Statistics are result of empirical sorts for each location over the global grid 9 8 7 6 5 4 3 Worst Site 95% Vertical Error 2 Global 95% Vertical Error 1 0 0 5 10 15 20 25 30 Day of Month (June 2000) Figure A-5-8. Typical Example of GPS SPS SIS Vertical Performance – June 2000 A-5.4 SPS SIS Time Transfer Accuracy Characteristics The SPS Performance Standard witnesses a transition to a different type of metric for SPS time transfer of UTC as defined by the United States Naval Observatory (USNO). The new metric is more in line with the basic stand-alone time transfer application, in that it assumes operations from a surveyed point and functions based upon an ensemble averaging of pseudo range residuals from all satellites in view. This metric removes performance variations due to geometry and leaves only those variations due to the statistical combination of UREs from all satellites in view over the sample interval. Figure A-5-9 illustrates the lack of time transfer performance Page A-29 October 2001 GPS SPS Performance Standard impacts due to satellite removal. Figure A-5-10 shows a 30-day trend of time transfer performance, over the month of June 2000. ANALYSIS NOTES Time Transfer Global Average 95% 3-20 11-31 11-20 20-26 9-11 10-24 9-10 4-20 2-11 3-31 3-11 11-24 9-24 1-25 11-26 4-11 10-26 Time Transfer Worst Site 95% 17-26 20-25 21-26 2-26 24-26 9-26 4-9 8-26 6-26 9-25 11-25 4-24 17-25 - Ensemble average of SPS SIS UREs each minute over 24 hours, at each location in global grid - 4 ns (1σ) noise in USNO measurement of GPS-UTC (USNO) bias and error values - 95% sort over 24 hours at each location 4-26 10 9 8 7 6 5 4 3 2 1 0 25-26 95% Ensemble Time Transfer Error (ns) GPS SPS All-in-View Ensemble Time Transfer Performance Worst Cases of Two PRN Combinations Out Figure A-5-9. GPS SPS Time Transfer Accuracy as Function of Two Satellites Removed GPS SPS Global Time Transfer Performance -- June 2000 95% Time Transfer Error (nanoseconds) 10...
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