To generate a global estimate of electron density

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Unformatted text preview: /Hz) 400 350 300 8 June 2000 250 179.9 200 150 170.7 100 50 3 June 2000 Data Courtesy of NOAA 0 April-90 April-91 April-92 April-93 April-94 April-95 April-96 April-97 April-98 April-99 April-00 April-01 Date (1 April 1990 - 31 March 2001) Figure A-5-11. Solar Flux Index Eleven Year Trend Errors in the GPS single-frequency model presented in ICD-GPS-200C dominate singlefrequency system URE performance. The contributions of the single-frequency model to URE are not however uniform, and in fact vary significantly on a global basis. Figure A-5-12 illustrates the range of error contributions to system URE made by the single-frequency model, and contrasts those contributions to the other elements that comprise the total URE. As shown in Figure A-5-13, single-frequency system URE can vary greatly throughout the global service volume. Performance around the equator was significantly worse than that experienced at mid to high latitudes. Longitudinal variations were due primarily to the angular offset of the geographic and geomagnetic equators. RMS single-frequency system UREs were on average 4.3 times worse than dual-frequency system UREs on a global basis. RMS single-frequency system UREs at worst case sites were on the order of seven times or more worse than the corresponding dual-frequency system URE statistic. SPS single-frequency positioning performance is necessarily affected by errors in the singlefrequency model. The shaded areas in Figure A-5-14 show locations on 8 June 2000 where 95% horizontal performance was greater than 10 meters for all-in-view receivers, while Figure A-5-15 provides the same information for 95% vertical errors greater than 25 meters. Areas of increased error form bands about the geomagnetic equator. Figure A-5-16 indicates the cumulative distribution of 95% horizontal and vertical errors on a global basis. On 8 June 2000, 95% of the Page A-31 October 2001 GPS SPS Performance Standard Earth’s surface experienced better than 16.4 meters horizontal (95%) performance, and better than 29 meters vertical (95%) performance. Similar results were found on 3 June 2000. Elements of SPS User Range Error Ionosphere Model - Worst Site Ionosphere Model - Global Average ANALYSIS NOTES Ionosphere Model - Best Site - Single-frequency ionosphere model error data from 8 June 2000, estimated using AFRL PRISM model data - Satellite orbit and clock error data from June 2000, based on GPS MCS log datasets - Troposphere error statistic based on average relative humidity, temperature and pressure Satellite Clock -- June 2000 Receiver Noise (GPS ORD) Orbit -- June 2000 C/A Code Phase Bias -- June 2000 Troposphere Model NAV Message Curve Fit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 RMS URE Contribution (meters) NAV Message Curve Fit RMS Contribution to URE (m) Troposphere Model C/A Code Phase Bias -- June 2000 Orbit -- June 2000 Receiver Noise (GPS ORD) 0.20 0.25 0.27 0.57 0.80 Satellite Clock -Ionosphere June 2000 Model - Best Site 1.43 Ionosphere Mo...
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This document was uploaded on 09/26/2013.

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