Towards daily-based local ties at Fundamental Geodetic Sites - Development of local tie processes as a part of the renovations at Metsähovi Geodetic Research Station

In order to function, modern society requires reliable and up-to-date spatial information. Current positioning methods work in a global reference frame, which is the result of a decades-long time series of space geodetic observations, updated approximately every five years. The reference frames of different space geodetic techniques are connected to each other by local ties, the vectors between the reference points of space geodetic instruments. An important role is played by geodetic stations with more than one space geodetic instrument, one of which is the Metsähovi Geodetic Research Station. The accuracy requirement for local tie vectors is 1mm/200m. In addition, the vectors must be oriented to the global reference frame. In this dissertation, two different techniques to measure and calculate the local tie vectors between the reference points of space geodetic instruments was investigated. The first technique is based on kinematic GPS, while the second is based on the precise angle and distance measurements. The GPS antennas, prisms or targets on the structure of the VLBI telescope rotate with the telescope. The coordinates of the reference point were estimated using the coordinates of the prisms or antennas with the mathematical model developed in this work. Although local tie measurements are field survey measurements, the accuracy requirements are the same as in precise industrial measurements or metrology. Moreover, this research includes investigations of measurement and analysis methods of local small terrestrial geodetic networks, and how to connect the networks to the global reference frame. Since GPS is a central part of the measurements in this work, the variation of the phase centre of the GPS antennas during the measurements constitutes a source of uncertainty that must be taken into account. This is handled in the data processing with calibration tables. The method to validate the calibrations of GPS antennas was developed in this dissertation, and the dedicated test field for this purpose was built at Metsähovi. The most important result of this dissertation that affects the combination of global reference frames, is the set of local tie vectors which are in the global ITRF2014 reference frame and meets the accuracy requirements of local ties needed in combinating the global reference frames. In addition, up-to-date automatic methods for measuring and calculating GNSS-based and terrestrial local ties were developed. Accurate local tie vectors improve the quality of global coordinate systems and are an important part, one technique, of global coordinate system integration. In addition to the global impact, this research benefits normal field measurements.