Response prn 15 anomaly page a 24 october 2001 gps sps

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Unformatted text preview: ge performance in terms of parameters under direct operational control. Although this standard definition approach has significant advantages in managing GPS performance, the standards cover only a portion of the total service an SPS user will experience. To mitigate this limitation in the standards definition, estimates are provided in Section A-5.5 of end user performance behaviors a single-frequency receiver may experience on an “average” day during solar maximum. Two final aspects of accuracy of concern to civil users and in particularly differential service providers are range rate error and range acceleration error. Previous documents provided performance standards for these two parameters that reflected limits on the contributions of SA. With the termination of SA, users experience range rate error and range acceleration error behaviors that are primarily products of the receiver environment, with infrequent transients due to satellite navigation uploads or internal satellite design idiosyncrasies (discussed in Section A4.4). The discussion in Section A-5.6 focuses on steady state characteristics of range rate and range acceleration error. A-5.1 Geographic Variations in SPS SIS Positioning Errors GPS position errors change as a function of latitude primarily due to constellation geometry, as shown in Figure A-5-1. As seen in Figure A-5-1, performance can be asymmetric between Southern and Northern latitudes. This asymmetry is caused by variations in URE due to satellite upload patterns, and variations in constellation geometry due to short-term satellite maintenance outages. Vertical accuracy is affected significantly more by latitude than horizontal error, due to the nature of the constellation geometry. Vertical accuracy suffers significantly above approximately 55° latitude (north or south) due to the lack of satellites at high elevation angles over the poles. Horizontal accuracy degrades mildly at mid-latitudes due to worsening horizontal geometry as latitude increases. However, horizontal accuracy begins to improve above approximately 45° latitude (north or south) as satellites visible from the other side of the Earth begin to enter into the position solution geometry. Figure A-5-2 illustrates how accuracy varies as a function of longitude. The primary element in longitudinal variation of accuracy is the navigation upload patterns of the GPS satellites. A large percentage of satellites are uploaded over the continental United States or shortly before the satellites enter visibility over Europe. This trend can be seen very clearly in the vertical component in Figure A-5-2 and less clearly in the horizontal component. Page A-25 October 2001 GPS SPS Performance Standard Example of GPS SPS Position Accuracy as Function of Latitude 1 June 2000 8 ANALYSIS CONDITIONS 7 - 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...
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