Weekly inter-technique combination of SLR, VLBI, GPS and DORIS at the solution level

Abstract

Constructing and maintaining a stable terrestrial reference frame is one of the key objectives of fundamental astronomy and geodesy. The datum realization for all the global terrestrial reference frame versions such as ITRF2014 and its predecessor ITRF2008, etc. is by assuming linear time evolution for transformation parameters and then imposing some conditions on these Helmert transformation parameters allowing defining the combined frame of the long-term solution at a reference epoch and its time evolution. By definition, ITRF adopted only linear motion of the Helmert parameters with uncertainty, while some publications have shown that translation-related uncertainties are underestimated. In this paper, we investigate a new approach, which is based on weekly estimation of station positions and Helmert transformation parameters from a combination of the solutions of four space-geodetic techniques, i.e., SLR, VLBI, GPS and DORIS. For this study, an interval of one week is chosen because the arc length of the SLR solutions is seven days. The major advantage of this weekly estimated reference frame is that both the non-linear station motions and the non-linear origin motion are implicitly taken into account. In order to study the non-linear behavior of station motions and physical parameters, ITRF2008 is used as a reference. As for datum definition of weekly reference frame, on the one hand SLR is the unique technique to realize the origin and determine the scale together with VLBI, on the other hand the orientation is realized via no net rotation w.r.t ITRF2005 on a subset of core stations. Given the fact that without enough collocations (i.e., at least three co-located stations) an inter-technique combined TRF could not exist, the selection and the relative weight of the local ties surveyed at co-location sites is a critical issue. To get stable results, we first assume that, if there were no events such as equipment changes between the measurement epoch of local tie and that of spacegeodetic solution (this time span called the stable period hereafter), the relative position between the two co-located stations should be invariant and this local tie could be used for computing the inter-technique combined reference frame in those weeks during the stable period of this tie. The resulting time series of both station positions and transformation parameters are studied in detail and are compared with ITRF2008. The residual station positions in the weekly combined reference frame are usually in the range of two millimeters without any periodic characteristic, but the residual station positions by deducting the regularized station position in ITRF2008 may reach a magnitude of a few centimeters and seem to have a significant annual signal. The physical parameters series between the weekly reference frame and the ITRF2008 also show the obvious existence of annual signal and reach a magnitude of one centimeter for origin motion and two ppb for the scale. 2 Li-Zhen Lian et al.

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“…A unique standard terrestrial reference frame (TRF) is fundamental to ensure interoperability and consistency of geodetic products and to adequately exploit various measurements collected by ground-based sensors, or via artificial satellites for Earth science and geodesy applications [1][2][3], including plate tectonics [4,5], co-seismic and post-seismic deformations [6,7], global geophysical fluid dynamics [8,9], ice melting [10], accurately determining point positions, and the rate of sea level rise [11,12], etc.…”

Reduction of satellite signature effect in high accuracy satellite laser ranging to Etalon

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