Changes in the multipath value at ASG-EUPOS GNSS reference network stations in 2010-2021

The multipath phenomenon is one of the factors affecting the accuracy of GNSS positioning. It results from reflections of the satellite signal from objects in the vicinity of the GNSS antenna. There are groups of techniques that allow minimizing the impact of this error on positioning results. These include: antenna placement, the use of the appropriate type of antenna, the use of a professional receiver as well as proper post-processing of observations. However, it is impossible to completely eliminate the influence of multipath on the measurement results. In the case of carrier phase differential positioning, this error has two main effects. First of all, the multipath increases the initial search space for correct ambiguities. Consequently, the accuracy of the vector solution between the reference station and the rover receiver is affected. The authors of this article examined how the characteristics of the multipath error changed at the stations of the Polish network of ASG-EUPOS reference stations in 2010-2021. Two computational strategies were adopted to determine the multipath: Code Minus Carrier linear combination (CMC) and pseudorange multipath observable (MP). Based on the research, it was found how the multipath values changed depending on the change of the receiver and the terrain around the reference stations. It was determined which stations had high multipath values in 2010 and what changes occurred over the 11 years. Based on the carried out analyses, it was also recommended to perform periodic tests that would allow it to detect incorrect configuration or incorrect operation of receivers.