With the advent of modern space geodetic techniques Geodesy has undergone a profound transformation. These methods enable precise measurements of the Earth’s shape, rotation, and orientation in space. Moreover, they play a crucial role in monitoring the Earth’s atmosphere and observing geophysical phenomena. They serve both scientific research and practical applications.This study leverages GNSS-based applications, which hold a prominent position among space geodetic techniques. They enable precise estimations of the pole coordinates (x, y) and the length of day (LoD), collectively referred to as Earth Rotation Parameters (ERPs). Highly accurate ERP time series are essential for understanding the complex dynamics of the Earth and establishing precise reference systems. Most navigation and positioning applicationsbenefit from this. Thanks to a comprehensive network of globally active GNSS stations, global coverage is ensured, allowing for an unprecedentedly accurate determination of ERPs.However, several error sources that affect the GNSS signal travel time between the satellite and the receiver must be considered. A major error source is the ionosphere, a medium dispersive for microwaves, causing signal delays as the signals pass through the Earth’s atmosphere to ground-based receivers. By using observations on two frequencies, it is possible to eliminate a significant portion of this delay with the so-called ionosphere-free linear combination. On the other hand, the geometry-free linear combination of multi-frequency observations enables the creation of ionospheric models and thus the description of ionosphericstate variables. These models can then be used to calculate travel time corrections for observations from mass-market single-frequency receivers.The aim of this work was to estimate and analyze the aforementioned Earth Rotation Parameters (ERPs) as well as ionospheric information in the form of VTEC (Vertical Total Electron Content) maps. For this purpose, a combination of GPS and Galileo observations was processed to assess the extent to which these solutions are improved by using multi- GNSS combinations versus GPS-only data.Special attention is given to the European Galileo system. Since the launch of its first test satellite in December 2005, Galileo has played a crucial role as a complement to established GNSS systems such as the American GPS and the Russian GLONASS. The study shows that combining Galileo with GPS observations significantly improves accuracy in precise parameterestimation, provided that high-precision orbit data based on new radiation pressuremodels are available for Galileo.The methodology for this research involved processing observation data in the Bernese GNSS Software version 5.2 (BSW). Observations from a globally distributed network of GNSS IGS stations were used to estimate ERP (Earth rotation parameters) time series. Six solutions across 1-day and 3-day arcs were calculated, depending on the combination of observations (GPS-only or GPS+Galileo combined) and the radiation pressure model used.Additionally, a detailed regional ionosphere model covering mid-latitude Europe was generated using data from GNSS IGS and EPOSA (Echtzeit Positionierung Austria) permanentstations, employing the modified single-layer mapping function (MSLM) and the geometry free linear combination. Results were validated against established models, highlighting significant improvements when integrating multi-GNSS data.The contribution of this study is reflected in the demonstration of improved accuracy, which can be achieved through multi-GNSS integration, in this case in ERP and ionospheric modeling. The findings verify the importance of utilizing multiple GNSS systems for precise geodetic applications. Thus, it is recommended that combined observation data be relied on for future improvements.The accuracy improvement for ERPs is approximately 25%, while the VTEC estimates couldbe improved within the range of 60% during summer months up to 80% in winter, with respect to external reference models.