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GPS APPLICATIONS AND REQUIREMENTS 50 Table 2-8 GPS Earth Science Requirementsa Application Accuracy (2 drms) Integrity (time to alarm) Static Meteorology 0.001 m Hours Oceanography- General Ocean Circulation 0.01 m Hours Determination Geodynamics 0.001 m + 109 x baseline length Hours Dynamic Oceanography - real-time Positioning and 10.0-30.0 m Not specified Navigation Airborne Geophysics 3.0 m vertical Minutes a.Integrity (1 minus PHE times PMD), availability, continuity of service, and resistance to RF interference requirements are not available for the GPS Earth Science applications covered by this table. Other requirements were derived from input received from the appropriate scientific community. Challenges to Full GPS Utilization Meteorology A third GPS radio frequency would be very helpful in atmospheric studies. Also, the presence of A-S greatly increases costs and limits the performance of many techniques due to loss of low-elevation angle data and signal-to-noise ratio, even when using dual-frequency codeless receivers. Oceanography In general, spacecraft orbits determined from GPS data with A-S off are superior to those determined by other means, with A-S on this is not the case. A successor mission to Topex/Poseidon could be designed with receivers that would work well in the presence of A-S and, essentially, overcome this obstacle. However, it has been estimated that the additional cost of adding a space-qualified PPS receiver to a satellite would be about $500,000.38 Much of this cost stems from the security measures that are required for the proper handling of classified equipment. For other types of oceanographic research, SA is the central challenge to the usefulness of GPS. The 10- meter to 30-meter accuracies required to navigate research vessels, position buoys, and locate objects on the ocean floor cannot be achieved using GPS 38 W. G. Melbourne et al., "GPS Flight Receiver Program for NASA Science Missions - A Unified Development Plan," (JPL D-10489). Jet Propulsion Laboratory, 10 February 1993.