[G01-4] Combination and co-location of space geodetic techniques

[G01-4-04] Multi-Year Analysis of GNSS Local Ties at Fundamental Sites

^○Ivan Dario Herrera Pinzon, Markus Rothacher (Swiss Federal Institute of Technology in Zurich (ETHZ), Zurich, Switzerland)

With increasing requirements on accuracy and stability for the realisation of the International Terrestrial Reference System (ITRS), the comprehensive analysis of technique-specific systematic biases in local measurements becomes crucial for the improvement of ties among space geodetic techniques. The quality of the ITRS realisation, the International Terrestrial Reference Frame (ITRF), relies on the adequacy of the ties of individual space geodetic techniques at fundamental sites. To this end, intra-technique co-location, where two or more co-located instruments of the same technique are available, constitutes an essential step for analysing individual biases on short baselines. Although Global Navigation Satellite Systems (GNSS) are one of the major contributors to the realisation of the ITRF, discontinuities in time series associated with hardware and software changes pose a major threat for their proper utilisation. Co-located GNSS at fundamental sites provide the opportunity of improving the accuracy of estimated positions by examining data breaks, local biases, deformations, time-dependent variations and the comparison of GNSS baselines with existing local tie measurements. Typically equipped with an array of several GNSS receivers collecting data continuously for several years, their proximity grants similar tropospheric delays, identical ionospheric conditions, same loading effects and nearly identical station motion.

With the use of precise GNSS orbits, an ambiguity fixing strategy and an appropriate parameterisation, this contribution presents a global multi-year analysis of a subset of IGS fundamental sites for delivering homogeneous coordinate time series and phase residuals, based on L1, L2 and the ionosphere-free linear combination with and without troposphere estimation, to quantify hardware and software changes, antenna patterns, environmental effects, local deformations and other time-dependent variations of the local baselines.