On the impact of local ties on the datum realization of global terrestrial reference frames

摘要

Local ties (LTs) at co-located sites are currently used to combine different single-technique solutions to determine global terrestrial reference frames (TRFs). We assess by simulations the impact of different LT standard deviations, biased LTs and a selection of LTs on the datum realization of global TRFs. The simulations are based on Global Positioning System (GPS), Satellite Laser Ranging, and Very Long Baseline Interferometry (VLBI) observations covering the time span 2008-2014. We find that LT standard deviations of 1cm and better yield differences in the TRF-defining parameters below 1mm. VLBI is most affected by altering the LT standard deviations, especially in the translations since VLBI is inherently not sensitive to the origin of the TRF. Altering the standard deviations of the LTs applied in ITRF2005, ITRF2008, ITRF2014 results in small differences reaching a maximum of 0.6mm at the VLBI stations. Simulating technique-wise biased LT stations shows the largest differences in the TRF-defining parameters of more than 2mm, if all GPS LT stations are biased by 1cm, proving that GPS plays the major role in the connection of the three techniques. Simulating single biased LT stations by 1cm in either the north, east, or height component indicates small differences of less than 0.8mm in the TRF-defining parameters, the largest differences result at LT stations located on the southern hemisphere. The selection of LTs demonstrates that the southern hemisphere LTs are very important, especially for the realization of the scale.