Integrating High Resolution Terrain Data into Global PDOP Calculations

Mark A. Staley, Michael A. Brilleslyper

Abstract:	This study incorporates terrain data on a near-global basis to determine GPS satellite line-of-sight visibility. The resulting PDOP-based metrics are more realistic than those produced by standard models that apply a single isotropic mask angle. Shuttle Radar Topography Mission (SRTM) data were used to construct terrain masks at over 23 billion locations between 60° North and South latitudes. Composite masks were created by combining these terrain masks with an isotropic 5° receiver mask. Using the composite masks, the Position Dilution of Precision (PDOP) was calculated at these 23 billion locations for 4 different constellation configurations over the sidereal day in 1 minute time-steps. For a PDOP < 6 threshold, the average global availability ranged from 99.92% for a 27-satellite constellation to 99.99% for a 33-satellite constellation. Similarly, for a PDOP < 6 (98% minimum availability) threshold, global coverage ranged from 99.10% to 99.85% for 27 and 27+6 geostationary satellite constellations, respectively. As threshold specifications are tightened up, the divergence between the availability and coverage metrics becomes more pronounced. For example, for a PDOP < 3 (98% minimum availability) threshold, global coverage ranged from 93.58% to 98.40% for 27 and 27+6 geostationary satellite constellations, respectively. Therefore, we show parametric results for coverage over a range of threshold specifications. A terrain mask database was generated as a product of this work, and can be used to rapidly reconstruct terrain masks at ground level. These terrain masks can be used in any application that requires line-of-sight determination between a satellite and a position on the ground.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2692 - 2699
Cite this article:	Staley, Mark A., Brilleslyper, Michael A., "Integrating High Resolution Terrain Data into Global PDOP Calculations," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2692-2699.
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