Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.g11a..02o&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #G11A-02
Astronomy and Astrophysics
Astronomy
1229 Reference Systems, 1241 Satellite Geodesy: Technical Issues (6994, 7969), 1244 Standards And Absolute Measurements, 1294 Instruments And Techniques
Scientific paper
In the Global Positioning System (GPS) measurements of the satellite coordinates and the underlying World Geodetic System 1984 (WGS 84) reference frame are derived from observables such as pseudorandom noise (PRN) signals, and carrier phase, which are referenced to on-board atomic clocks. Systematic errors exist in both the estimated satellite coordinates and the reference frame. The reference frame utilizes external inputs in the form of International Terrestrial Reference Frame (ITRF) coordinates and constrains the results to be compatible with the ITRF coordinates for a set of global reference stations. The ITRF is, in turn, obtained from the combined analysis of GPS, Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) data. The current realization of the reference frame could be described as circular in that an independent method of external verification is currently not available. To ensure the continued successful operation of the GPS it is necessary to have the capability of analyzing systematic errors by an independent means from current radiometric observables and data from foreign sources. In practice, accuracy of the standards used for measurement should be better than the expected, required operational measurement accuracy by a factor of ten to ensure that the desired requirement is met. Currently, the accuracy of both the ITRF and the WGS 84 is estimated to be on the order of 1 to 2 parts per billion, leading to expected drifts of 0.6 to 1.2 cm per year. The experience of the last three decades has indicated an approximate improvement by a factor of ten per decade. Therefore, while current accuracy of the ITRF and WGS 84 reference frames marginally meets civilian and military requirements, it is very likely that, within the lifetime of GPS III, the accuracy of the reference frames will be unable to meet the anticipated requirements. This report examines to address the emerging capability gap. These include: (1) Increased Frequency of Satellite Clock Updates; (2) Radiometric Tracking at Higher Frequency; (3) Laser Tracking; (4) Astronomical Geolocation; and (5) GPS Intersatellite Links.
Brodsky B. L.
Labrecque J. J.
Miller Jason J.
Moreau Mathieu
Nelson Randy
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