Technical description of ivs2017a_dsnx: ======================================= VLBI combination group of the Federal Agency for Cartography and Geodesy (BKG), Germany (Sabine Bachmann, sabine.bachmann(at)bkg.bund.de, ccivs(at)bkg.bund.de) March, 2017 The ivs2017a_dsnx series is a combination product by accumulation of normal equation matrices. The normal equation matrices in these files are unconstrained (datum-free). Input series are currently contributed by BKG, CGS, DGFI, GFZ, GSFC, IAA, OPA and USNO. Analysis center: | Software: -----+-------------------------------------------------------------+----------- BKG | Bundesamt fuer Kartographie und Geodaesie, Leipzig, Germany | CALC/SOLVE CGS | Centro di Geodesia Spaziale, Italy | CALC/SOLVE DGFI | Deutsches Geodaetisches Forschungsinstitut, Munich, Germany | OCCAM/DOGS_RI GFZ | German Research Center for Geosciences | VieVS@GFZ GSFC | Goddard Space Flight Center, Washington D.C., USA | CALC/SOLVE IAA | Institute of Applied Astronomy RAS, Russia | QUASAR OPA | Paris Observatory, Paris, France | CALC/SOLVE USNO | U.S. Naval Observatory, Washington D.C., USA | CALC/SOLVE -----+-------------------------------------------------------------+----------- Purpose of this solution: ========================= The main objective of ivs2017a_dsnx is to provide IVS combination ofthe rigorous determination of station positions and earth orientation parameters. Detailed description: ===================== This approach of combining VLBI solutions is based on the principle of addition of normal equation matrices and thus begins at an earlier step of analysis. This approach is also known as "Adjustment of groups of observations". This approach uses datum-free normal equation matrices of VLBI sessions which are provided as SINEX files. The combination is performed in the following way: Apriori epochs: --------------- Before accumulating the individual normal equation matrices the matrices are transformed to the mean epoch of all contributions (they may differ by a few minutes) by using the respective EOP rates. Apriori values: --------------- Furthermore the individual normal equation matrices have to be transformed to a common set of apriori values. For station coordinates a TRF (aligned to ITRF2014) computed from all SINEX files available between 1979 and today, for the earth orientation parameters the 14C04 values are used as apriori values for the normal equation matrices of all analysis centers. These values are listed in the SOLUTION/APRIORI-block. Generation of SINEX file for accumulated solution: -------------------------------------------------- After applying scaling factors the normal equation matrices of the individual solutions are accumulated. The resulting normal equation matrix is then written into a new SINEX file (DATABASE_CODE_ivs2017a.snx). Since the original normal equation matrices are datum-free or singular, the accumulated normal equation matrices are still datum-free. So there is no SOLUTION/ESTIMATE section in this file, since no datum information has been imposed. Estimated parameters: ===================== Parameters combined are: ALL station coordinates, x-pole, y-pole, UT1-TAI, x-pole-dot, y-pole-dot, LOD, dX, dY. As mentioned before there are no estimated parameters at all since there is no datum information imposed. Software: ========= - The processing of the individual matrices is done using a software from the German Geodetic Research Institute (DGFI), Munich, called DOGS-CS. - A software called combine_sinex has been developed initially at the Geodetic Institut of the University of Bonn and adapted at the Federal Agency for Cartography and Geodesy (BKG) and is used to process the input SINEX files, perform checks of the input data, to compute scaling factors and to visualize results. Contact: ======== Federal Agency for Cartography and Geodesy (BKG) VLBI combination Group Richard-Strauss-Allee 11 D-60598 Frankfurt am Main Germany eMail: sabine.bachmann(at)bkg.bund.de or ccivs(at)kg.bund.de website: ccivs.bkg.bund.de