Direct Geocentric Realisation of the American reference frame by combination of geodetic observation Techniques (DIGERATI)
Final Report Abstract
The overall goal of the project DIGERATI was to study the feasibility and methodology of computing a regional geocentric epoch reference frame (epoch RGRF) with a stable datum directly from a combination of GNSS, SLR and VLBI observations. A central research topic was the realization of the geodetic datum from a station network that is variable from epoch to epoch. This regards in particular SLR which is required for obtaining the origin of the frame and (in combination with VLBI) its scale. In this context the benefit of the new geodetic observatory AGGO is of special interest. Due to a lack of real observation data from AGGO during the project period, extensive simulation studies for SLR were performed. As an outcome, it could be shown that AGGO will lead to significant improvements in the datum stability of an epoch RGRF, and the station will be of high relevance for an operational solution. Furthermore, the simulations clearly revealed that an enhancement of the existing SLR stations in South America would further stabilize the datum, and that additional SLR sites (besides AGGO) in e.g. Antarctica or the Pacific region would be valuable for improving polar motion and reference frame parameters. For the transfer of the datum to the regional GNSS network, an adequate number of colocation stations (SLR/GNSS, VLBI/GNSS) is required. One aspect of the project was thus to investigate how far the GNSS network has to be extended beyond the SIRGAS network, i.e. to find the minimal GNSS network configuration, in order to transfer the datum from SLR/VLBI reliably. In this frame, different scenarios were evaluated. The studies showed that the GNSS network should include all available SLR/GNSS and VLBI/GNSS co-located stations worldwide to ensure the availability of enough common sites also when some SLR or VLBI stations are out of operation. But as most of these stations are located in the northern hemisphere, this station distribution is not optimal for GNSS data processing. To ensure a homogeneous global distribution of the network it is recommended to include all the core stations of the IGS global network. In the frame of the GNSS processing for this project, also two improved versions of the velocity model for Latin America and the Caribbean (VEMOS2015/2017) were computed and published. They provide a comprehensive picture of the present-day surface deformation in the region caused by ongoing geodynamic processes. The identification of the optimal combination strategy of GNSS, SLR and VLBI involved an analysis of the available precise local ties and of the relative weighting of the three techniques. Furthermore it was studied, in which interval the epoch RGRF can be realized as a trade-off between temporal resolution and stability. For the period between 2002 and 2016, it could be shown that a weekly epoch RGRF solution – corresponding to the current sampling of the SIRGAS operational solution – can be realized with satisfying datum stability. The good quality of the datum transfer from SLR to the regional combined solution has been evidenced by a validation against the ITRF2014. A comparison with the SIRGAS operational solution revealed deficiencies of the latter: An offset and a seasonal variation in the z-translation (indicating a periodic North-South displacement of the SIRGAS frame) demonstrate that the origin of the SIRGAS operational solution does not coincide with the geocenter. The seasonal variation in z, related to seasonal variations in the Amazon basin, lead to the conclusion that the datum of the current SIRGAS operational solution is affected by the instability of its datum stations. This, in turn, demonstrates the potential of an epoch RGRF for which a strategy has been elaborated with this project. The outcome of this project thus provides the basis for further investigations with the goal to implement the results in a future operational SIRGAS epoch RGRF.
Publications
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Crustal deformation and surface kinematics after the 2010 earthquakes in Latin America. Journal of Geodynamics, 102, 1-23, 2016
Sánchez L., Drewes H.
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Epoch reference frames as short-term realizations of the ITRS - datum stability versus sampling. In: Rizos C., Willis P. (Eds.), IAG Symposia 143, 26-32, 2016
Bloßfeld M., Seitz M., Angermann D.
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SIRGAS core network stability. In: Rizos C., Willis P. (Eds.), IAG Symposia 143, 183-190, 2016
Sánchez L., Drewes H., Brunini C., Mackern M.V., Martínez-Díaz W.
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Future global SLR network evolution and its impact on the terrestrial reference frame. Journal of Geodesy, 92(6), 625–635, 2017
Kehm A., Bloßfeld M., Pavlis E. C., Seitz F.
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Consistent estimation of geodetic parameters from SLR satellite constellation measurements. Journal of Geodesy, 92(9), 1003–1021, 2018
Bloßfeld M., Rudenko S., Kehm A., Panafidina N., Müller H., Angermann D., Hugentobler U., Seitz M.
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Future TRFs and GGOS – where to put the next SLR station? Advances in Geosciences, 50, 17–25, 2019
Kehm A., Bloßfeld M., König P., Seitz F.
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(2020) Geodetic Monitoring of the Variable Surface Deformation in Latin America. In: . International Association of Geodesy Symposia. Springer, Berlin, Heidelberg. S. 1-12
Sánchez L., Drewes H.
