SNARF Working Group - Report of the Second SNARF Workshop

Eos Trans. AGU, 85(17), Jt. Assem. Suppl., Abstract G21C-03, 2004

Test of a Center of Lateral Figure (CL) reference frame for a global GPS network

Johnson, D J
E-mail: djess.washington.edu
Address: University of Washington, Earth and Space Sciences Box 351310,
Seattle, WA 98195-1310 United States

Seasonal degree-one deformation related to loading effects are a source of significant misfit between observed site coordinates and assumed positions that are based on a linear center of surface figure (CF) reference frame. This discrepancy is partly absorbed by apparent annual variations in the GPS "scale" parameter which, in turn, spreads annual deformation artifacts to sites elsewhere on the Earth’s surface. In the presence of degree-one deformation, a suitable reference frame model should allow for non-linear site motion. The Center of Lateral Figure (CL) reference frame is one possible solution. With the CL model, station motions are constrained to move with constant horizontal velocities, and the vertical velocities are unconstrained. This confines degree-one deformation to the unconstrained vertical component. A CL reference frame model is demonstrated here using the results of a GIPSY/OASIS II fiducial-free analysis of over 100 globally distributed GPS sites. The reference frame model utilizes only the horizontal component of site positions and the GPS "scale" parameter is neglected in the initial solution. Preliminary results show that seasonal deformation is placed in the vertical component, as expected, and that the geographical distribution of seasonal signals is consistent with degree-one loading models. An additional finding from this test is that the WRMS scatter in daily horizontal site positions is reduced. This is likely due to reliance on the precise horizontal component, and omission of the noisier vertical component. The result is that the horizontal scatter for stations in a global solution approaches the quality of a regionally-filtered solution. For analysis on a plate-wide to global scale, as is the case for SNARF, use of a CL frame with the vertical component unconstrained may be useful. With the vertical component unconstrained, horizontal positions are not biased by seasonal vertical motion and noisy vertical motion at sites located 90 degrees around the side of the earth. In turn, a precise datum for the local vertical component is realized using horizontal data from the same sites a quarter turn around the Earth.

Last modified: 2019-12-24  02:12:53  America/Denver