- Related Research Areas
- Earth Surface & Interior
The terrestrial reference frame (TRF) is the foundation for virtually all space-based and ground-based Earth observations. Positions of objects are determined within an underlying TRF and the accuracy with which objects can be positioned ultimately depends on the accuracy of the reference frame. For example, errors in the currently available TRFs could amount to as much as 15% of the observed sea level rise signal. The most accurate terrestrial reference frames currently available are those produced by the International Earth Rotation and Reference Systems Service (IERS). However, the two most recent realizations of the International Terrestrial Reference Frame (ITRF) produced by the IERS, namely ITRF2000 and ITRF2005, exhibit large differences with respect to each other. In the z-direction their origins differ by 5.8 +/- 0.3 millimeters (mm) in position and 1.8 +/- 0.3 mm/year in rate. These differences, or errors, in the origin of the TRF translate directly into errors in determining the positions of sites on the surface of the Earth. For example, over the surface of the oceans, an error of (-1.5, -2.2, -2.1) mm/year in the (x,y,z)-coordinates of the origin of the TRF translates to an error of 0.4 mm/year in mean sea level, a substantial fraction of the observed mean sea level rise of about 3 mm/year. A more accurate and stable realization of the TRF will allow better tracking of mass transport in the Earth system, including changes in sea level and the global water cycle that are associated with climate change. Much of the error in determining the TRF is caused by the inability to accurately tie together the independent VLBI, SLR, GNSS, and DORIS networks of reference stations. While a subset of reference stations in each network are collocated and their relative positions surveyed, such ties are too sparse to adequately align the independent networks. In our approach to determine the TRF we will align the networks by additionally using Earth orientation observations. Since all networks observe the Earth orientation parameters (EOPs), commonly observed EOPs can be used to tie the networks together We will also exploit the fact that collocated stations exhibit the same motion and we will develop techniques to significantly reduce aliasing effects of nonsecular station motion on the TRF. Our network alignment and reference frame determination will be done using a Kalman filter that will enable the incorporation of frequently observed single baseline VLBI as well as SLR and GPS length-of-day measurements, measurements that were not used in ITRF2005. This effort will build upon the extensive experience at JPL in using Kalman filters to both process GPS observations, determining station positions and reference frames, and to combine Earth orientation parameters. The studies proposed in this investigation will lead to: (1) an improved terrestrial reference frame, needed for numerous scientific and societal applications, not the least of which are sea level change studies; (2) an improved combined Earth orientation series, needed for numerous scientific investigations; and (3) improved consistency between the Earth orientation parameters and the terrestrial and celestial reference frames, needed when transforming station coordinates from the terrestrial frame to the celestial frame.
Project PI: Richard Gross/Jet Propulsion Laboratory
Jet Propulsion Laboratory, Mail Stop 238-600, 4800 Oak Grove Drive, Pasadena, CA 91109-8099
Email: Richard .Gross@jpl.nasa. gov
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