From all satellites in view this metric removes

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Unformatted text preview: ANALYSIS CONDITIONS 9 8 7 6 5 4 3 2 Worst Site 95% Time Transfer Error 1 Global 95% Time Transfer Error 0 0 5 10 15 20 25 30 - 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 ensemble averaging from known location - SPS signal-in-space UREs, with 50 cm of added noise to represent uncertainty due to Tgd - 4 nanosecond 1σ uncertainty in prediction of GPS time relative to USNO UTC - Five degree mask angle - Statistics are result of empirical sorts for each location over the global grid Day of Month (June 2000) Figure A-5-10. Typical Example of GPS SPS SIS Time Transfer Performance – June 2000 A-5.5 A Description of Single-Frequency Receiver Performance This section provides the civil community with estimates of single-frequency receiver performance that are representative of behavior during solar maximum. Single-frequency user performance is dominated by errors in the GPS single-frequency model representation of Total Electron Count (TEC) along the line-of-sight from the user to a GPS satellite. Errors in the GPS single-frequency model are primarily a function of solar flux density and its interactions with the Earth’s magnetic field and upper atmosphere. The information provided in this section was developed using PRISM model data supplied by the Air Force Research Laboratory (AFRL) and the Air Force Weather Agency (AFWA). PRISM Page A-30 October 2001 GPS SPS Performance Standard combines electron density and other measurements with a sophisticated model of the upper atmosphere to generate a global estimate of electron density over a specified time interval. Electron densities are provided every 15 minutes at a 1° x 1° grid spacing, at 50 different altitudes ranging between 70 and 1,600 kilometers. This information was used, along with orbit and clock prediction error estimates, receiver noise and troposphere model error estimates, to generate instantaneous single-frequency UREs every minute over the selected 24-hour interval for all satellites in view, for 1,666 locations spread uniformly over the surface of the Earth. These system-level URE values were then used to generate and accumulate statistics on estimates of instantaneous single-frequency user position errors. Solar flux density follows a trend established by the eleven-year solar cycle, at its peak as of this writing. Two days in June 2000 (3 and 8 June) were selected for assessment of typical singlefrequency performance at solar maximum, as shown in Figure A-5-11. When evaluated against values trended since 1 January 1947, 3 and 8 June 2000 fall at the 61st and 66th percentiles respectively in magnitude of solar flux density. This information serves to provide a rough assessment of where the evaluated days fall in the range of historical density values. Solar Flux Index Eleven Year Trend Daily Solar Flux Value (W/m^2...
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This document was uploaded on 09/26/2013.

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