The Scale of the Terrestrial Reference Frame from SLR and VLBI

Abstract:

The scale of the terrestrial reference frame has generally been determined from the satellite laser ranging (SLR) and very-long baseline interferometry (VLBI) techniques. However, there has been a persistent bias of roughly 1.5 ppb in the scale realized by these techniques. While this bias, on the order of 1 cm, might have been within a reasonable uncertainty when ITRF2000 was determined, it seems unlikely that this bias would persist with no significant change for ITRF2005, ITRF2008 and now apparently for ITRF2013. Consequently, it seems worth considering whether there is not a fundamental bias in the definition of these two frames, i.e. in the models that are used to realize these frames. In the case of VLBI, the relativistic ‘consensus model’ adopted in 1991 should be re-examined to be sure some small error was not overlooked. In the case of SLR, the scale is strongly influenced by the adopted value of the Earth’s gravitational constant (GM), which was also determined about the same time. The estimate of GM and the contributions to its uncertainty are re-examined to see how much of the bias between the techniques might be attributed to GM.