Validation of Components of Local Ties

Local ties (LTs) at co-located sites are currently used to align different space geodetic techniques for the determination of a global terrestrial reference frame (TRF). However, the currently available LT measurements are typically characterized by an inhomogeneous accuracy, which may cause inconsistencies within the TRF and limit the final TRF accuracy. An alternative strategy is a combination of common parameter types to which the individual geodetic techniques are sensitive. In this study, we combine Global Navigation Satellite Systems (GNSS) and Satellite Laser Ranging (SLR) data without using LTs but by combining the common pole coordinates and by adding proper datum constraints. In addition, we constrain the velocities at co-located sites to be the same for all markers. This allows an independent validation of measured LT components. Our data are based on a homogeneous reprocessing of GPS+GLONASS and SLR to LAGEOS-1 and LAGEOS-2 over 17 years in the time span of 1994–2010. A preliminary analysis including the elimination of outliers and the selection of core datum stations was performed based on the station position time series of the single-technique solutions. Applying our combination approach, the north and height components of the LTs can be directly derived from our combined coordinate solution. The differences of the measured and the estimated LTs remain below 1 cm for 96% in the north component and for 50% in the height component of all co-located sites.