The Assessment of Re-Processed GPS Satellite Products For Long-Term Monitoring of Geodynamic Processes

The successful application of the Global Positioning System (GPS) to the long-term monitoring of geodynamic processes depends on the homogeneity and consistency of the daily position time series of stations. Precise Point Positioning (PPP) techniques are an efficient method of producing such time series, but they depend on the availability of precise satellite orbit and clock products. Since 1994, such products have been provided with a few weeks delay by the International GNSS Service (IGS). However, changes to the IGS processing strategy over time make these products unsuitable for the long-term monitoring of geodynamic processes. To overcome this, the Analysis Centers of the IGS are undertaking a re-processing effort, to produce re-processed precise satellite orbit and clock products for the period since 1994, using the latest IGS processing strategy. This study focuses on using daily PPP position time series for a global network to assess the satellite orbit and clock products from the IGS re-processing (repro1) effort and similar products generated at the University of Nottingham using an in-house modified Bernese GPS Software version 5.0. As part of our quality assessment, comparisons between our own products and the repro1 products are carried out and presented in this study. The results indicate some inconsistencies between the different products and bring into question the suitability of the repro1 products for the most demanding applications in geodynamics.