GNSS permanent stations control by the means of local ties monitoring

Abstract

The paper presents the method of GNSS (Global Navigation satellite System) permanent stations control by the monitoring of local ties between GNSS and SLR (Satellite Laser Ranging) stations. Co-locations are defined as two or more instruments occupying very close locations, which are very precisely surveyed by ground measurements in all three dimensions. The vector determined by classical or satellite methods is called a local tie. Every change of stations position obviously results in change of local tie value. The comparison of two independent stations’ coordinates enable to distinguish the real movement of one of the stations, potential processing errors and equipment malfunction. The analysis were based on the data from several globally distributed GNSS-SLR sites. The data gathered between 1996–2012 by these two techniques were processed using coherent strategies (the same models and parameters were used). Monthly orbital arcs for laser observations were created basing on solutions from several SLR stations with the best solutions quality and the highest amount of observations. For GNSS stations coordinates determination about 130 sites belonging to the IGS (International GNSS Service) were selected: 30 with local ties to SLR sites and others basing on their geolocalization and solutions time series analysis. The GNSS and SLR station coordinates were expressed in ITRF2008 for the epoch of 2005. The GNSS solutions were reduced to the SLR markers positions using local ties values and then expressed in topocentric frame NEU for better interpretation. The analysis of differences between SLR and GNSS NEU coordinates proved that mutual control of two techniques can be helpful in detection of problems at specific GNSS stations like e.g. equipment failure or improper GNSS antenna’s calibration. Comparisons of different techniques results enable to distinguish stations specific causes of coordinates discontinuities and phenomena with wider range like earthquakes. In case of temporal disturbances the proper actions can be taken, but the permanent change of the coordinates force the necessary of another local tie determination, because of the importance of inter technique connection for global reference frame construction.