Improved determination of group delay variations (GDV) of GNSS transmitter and receiver systems

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GNSS code signals experience delays depending on their transmission and incidence an-gles, often called Group Delay Variations (GDV). They can be determined from multi-frequency GNSS observation data and be used as corrections for the code signals. Their use improves the results of all those GNSS applications that rely on accurate code obser-vations. In recent years a GDV determination method was developed at the Geodetic In-stitute of the TU Dresden. It is based on the analysis of code-phase-linear combinations and has been applied to observation data from globally distributed reference stations for the determination of elevation-dependent GDV of BeiDou-2 and GPS L1/L2 code signals applied.In this research project, the existing methodology of GDV determination will be extended in several aspects. The present parametrization will be enlarged to also cover azimuth dependencies of the GDV of transmitting and receiving systems. The methodology will be adapted to the many new signal frequencies and to additional satellite systems with their individual properties. An additional extension concerns the analysis of GNSS observations from LEO satellites, which provide another excellent data source for GDV determination. All these extensions will result in an overall methodology for GDV determination from GNSS observation data. Furthermore, its application will yield GDV correction data sets for all GNSS satellites and many geodetic GNSS receiving systems. In an additional working package, the potential of absolute GDV determinations from receiving systems at differ-ent orbital heights (earth’s surface, LEO orbits) will be analyzed in detail.