Direct Geocentric Realisation of the American reference frame by combination of geodetic observation Techniques (DIGERATI)
This project shall investigate the possibility of realising regional geocentric reference frames (RGRF) epoch-wise and directly, i.e. without the usual transformation onto a global reference system. Such reference frames are of particular importance in seismic active regions, where strong earthquakes (e.g. Chile 2010) produce large surface deformations (up to several meters), damage existent reference systems with station coordinates at a fixed epoch and linear coordinate changes (such as, e.g. the ITRF), and disable their use. Also seasonal variations of air pressure and water storage produce sub-annual coordinate changes on the centimetre-level and complicate the application of existing reference systems in the interpretation of environmental changes.
Regional reference frames are at present exclusively realised through measurements of the Global Navigation Satellite Systems (GNSS), which enable the local access to the global geocentric reference systems because of their large number of stations. In this project epoch RGRF shall be computed directly by combining GNSS with the geodetic techniques Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). The origin of the epoch solutions will be realised by SLR, the scale by a weighted mean of SLR and VLBI. An epoch-wise realisation (e.g. weekly, monthly,…) entails a variable SLR-Network configuration from epoch to epoch. This effect on geocentricity and a stable datum realisation needs to be investigated.
The project will be applied in practice to the geocentric reference frame for the Americas (SIRGAS). But once developed, the methodology may also be applicable for other regions in future, depending on the distribution of respective geodetic networks and the availability of observations.
This project is a scientific contribution to the implementation of the Argentine-German Geodetic Observatory (AGGO) that has been installed in La Plata, Argentina, in 2015. AGGO assembles the important geodetic observation techniques GNSS, SLR and VLBI and thus will be an important co-location station in the combination. In the frame of this project DGFI carries out fundamental research on the optimum combination strategy for the epoch-wise realization of SIRGAS with a specific focus of the benefit of AGGO for SIRGAS.
DIGERATI has also a huge practical benefit in the common application of the SIRGAS coordinates, e.g., in regional geodesy, cadaster, geographical information systems and land surveying.