The Copernicus Pod Service: Architecture, Results and Impact on Science

The Copernicus POD (Precise Orbit Determination) Service is part of the Copernicus Processing Data Ground Segment (PDGS) of the Sentinel-1, -2 and -3 missions (part of the European Copernicus Programme). A GMV-led consortium has developed, and it is operating the Copernicus POD Service being in charge of generating precise orbital products and auxiliary data files for their use as part of the processing chains of the respective Sentinel PDGS.Currently there are five Sentinel satellites in orbit (S-1 A&B, S-2 A&B and S-3A); S-3B is expected to be launched in April 2018, and it will complete the constellation of these three missions. Future C&D satellites are not expected before 2020.Sentinel-1 requires high accurate orbits for InSAR processing; accuracies of 10 cm (2D) RMS in less than 3 hours and 5 cm (3D) RMS in less than 20 days. Sentinel-2 is an optical mission, which does not requires high accuracy orbital products - 1 meter (2D) RMS in less than 30 minutes; however the goal of the Copernicus POD Service is to obtain the same accuracy as for Sentinel-1. Finally Sentinel-3 is an altimetry mission, which requires accuracies in the radial component of the order of 8-10 cm (radial) RMS in less than 30 minutes, 3-4 cm (radial) RMS in less than 36 hours and finally 2-3 cm (radial) RMS in less than 25 days.These satellites are all equipped with dual frequency geodetic-grade GPS receivers (on future C&D satellite it will be a GPS+GALILEO receiver). Additionally, Sentinel-3 is equipped with a laser retro reflector for Satellite Laser Ranging (SLR) and a receiver for DORIS tracking.By using similar orbital parametrizations, processing schemes, and inputs, the architecture of the Copernicus POD Service maximizes the synergies among the different missions to simplify the design and operations, and to obtain similar accuracy results across the three missions.Quality control of the CPOD orbits is done by direct cross-comparison with independent orbit solutions provided by the Copernicus POD Quality Working Group (AIUB, CNES, DLR, EUMETSAT, ESOC, TU Delft, TUM ...), each of them using a different POD strategy. With S-3, SLR and DORIS provide independent means to validate the orbit.This paper presents the Copernicus POD Service in terms of architecture, operations and orbital accuracy achieved by the different orbit products of the different missions. In particular it describes the architecture of the system, interfaces with the different centres (including the provider of GPS orbits and clocks and with the ILRS community), the physical models and POD strategy used, and the experience from processing routinely these different missions. This description if complemented with recent developments to process the new L2C GPS signals, and the future needs to process Galileo signals which will be available on the future C&D satellites.Then it describes the accuracy assessment of the products, and the different methodologies used for this, including the role of the Copernicus POD Quality Working Group. Finally, it describes the products generated to support scientific studies in areas like orbit modelling, ionospheric research, InSAR, altimetry, etc.