The aim of this study is to study the effects of datum definition on the estimation of vertical velocities at the continuous GNSS stations and campaign GNSS sites. The observations have been analyzed to measure the accuracy of vertical deformations derived from GPS stations depending on the definition datum of the geodetic network.
This investigation was carried out six campaign GNSS sites and twenty-one continuous GNSS stations operated by the National Permanent Network in Turkey (TUSAGA-Active) in the coastal regions of Turkey during the period 2001-2018. The GNSS observations were processed in the ITRF2014 reference frame using Bernese v5.2 software with different approaches based on four International GNSS Service (IGS) reference stations, which are thought to be less affected by tectonic movements.
The results show that the sensitivity of GNSS vertical velocities depends on the geometrical distribution of the reference stations and on the chosen set of reference stations that define the datum of the geodetic network. Moreover, the accuracy from the number of reference stations is one to three is less good than four or more reference stations, and the vertical velocities of our solution derived from four reference stations agree with those of the IGS solution.