Normal equation combination of VLBI and SLR for CONT14

Abstract

In this master thesis VLBI and SLR (SINEX-) data from a 15-day measurement campaign in 2014 are combined on the level of normal equations (NEQ). This combination method plays an import role for the generation of Terrestrial Reference Frames and follows an approach by the Deutsches Geodätisches Forschungsinstut (DGFI), which is considered as an alternative to the state-of-the-art method used at the Institut Géographique National (IGN) (ITRF derivation on solution-level). Thereby, residuals (dX) for VLBI and SLR ground stations are estimated by the Least Squares Adjustment (LSA) method and added to given a-priori coordinates. Thus an own terrestrial reference system is generated. Therefore definitions of the geodetic datum are tested. The two space geodetic techniques are connected via local ties at four Co-Location sites. They are implemented to the NEQs as conditions, fixing the distance between the respective observing units. The results are investigated with respect to differences between VLBI and SLR stations, as well as differences between the (inter-technique) combined solution and the technique eng specific individual solutions. It is shown that the VLBI system is more stable than the SLR system. However this is also based on the fact that the available VLBI data is more homogenous. Hence, they are also used for the definition of the geodetic datum. On average the residuals have a size of 1.5 cm, varying between and within the two techniques. Furthermore, the variation of scale between the systems was investigated. Results show that the radius of the earth (of approximated 6371 km) is about 1 cm longer in the VLBI system than in the SLR system. This indicates a difference in scale of 1.7 ppb, which is comparable to the results found by Altamimi et al. [2016] with the combination of VLBI and SLR data on solution level. This can contribute to a better understanding of technique specific characteristics, which are necessary in order to improve the accuracy of a global TRF. This thesis also points out relevant parameters and their influences on the combination of VLBI and SLR NEQs. Challenging aspects that need to be considered like discrepancies between individual reference systems are discussed.