Precise Multi-Technique Orbit Determination of the Sentinel Satellites

A significant contributing error source in the computation of the ITRF is the estimation of terrestrial ties, between geodetic reference points at colocation sites. The discrepancy in the description of the vectors, as determined through space geodetic observations and terrestrial surveying techniques, can be as much as 10 cm at certain sites.In response, in 2022, the European Space Agency proposed the GENESIS satellite mission which is a specially designed geodetic satellite equipped with the four space geodetic techniques i.e., LRA, GNSS, DORIS and VLBI to achieve an ITRF with a positional accuracy of one mm and a stability of 0.1 mm/year.Given the increase in the number of LEO satellites that are equipped with multiple geodetic techniques, it is opportune to assess and develop the capability of co-location in space (at the satellite) to achieve these accurate terrestrial ties at sites that are collocated with multiple space geodetic observing techniques.The aim of the of the study is to determine the feasibility of colocation in space by undertaking multi-technique orbit determination, estimating station coordinates and hence the terrestrial ties between collocated observing techniques using multi-technique data from the Sentinel satellites. This may inform the GENESIS geodetic mission.Our project estimates orbits for the available techniques on the respective satellites, from 2016 to 2022.  The observation network and its categorisation based on collocated systems, the computations standards implemented for each observation type and the subsequent combination method to determine the coordinates for each technique at each site is presented. The vectors as determined between adjusted station co-ordinates are compared to the official terrestrial ties. This measure may provide insight into the stacking and combining of POD solutions; and station position estimates that may be performed for optimum space co-location results and identify any limitations or potential improvements in the processing strategy.