The European Space Agency Tender

Accurate Reference Frames Are The Basis For Any Kind Of Navigation On Earth And In Space. Esa's Navigation Support Office (navso) Is Responsible For The Generation Of Terrestrial Reference Frames (trf) For Esa And European Union Missions And Is Contributing To The Generation Of The International Terrestrial Reference Frame (itrf).among Other Space Geodetic Observation Types, The Navso Is Processingobservations Of Gnss, Collected By Esa's Gnss Observation Network(egon). Gnss Observations Are Already Providing An Important Contribution To Trfs, But The Accuracy Of Their Contribution Is Still Limited By The Limited Knowledge On The Antenna Behaviour. The Publication Of The Galileo Phase Centre Information, For The First Time Provided Insight In The True Characteristics Of The Satellite Antennas.in Particular For Galileo, The Accuracy Limitation Is Now The Knowledge On The Ground Antenna Characteristics. Different Techniques Have Been Developed Tocalibrate The Antenna Characteristics, But Still, The Unavoidable Exchange Of Calibrated Geodetic Gnss Antennas Causes Coordinate Jumps And Results In Discontinuities In The Coordinate Time Series. Joint Analysis Ofsignals On Different Frequencies Or From Different Gnss Still Reveals Differences And Limits The Benefits Of Their Combination. All These Effects Clearly Limit The Benefit Ofgnss Observations For Plate Motion Analysis And Their Contribution To Trfs.the Aim Ofthis Activity Is To Identify The Influencing Factors On The Antennacharacteristics And To Optimise The Antenna Design And The Calibration Methods To Increase The Accuracy Of Gnss Observations To Reduce Coordinate Jumps And To Fulfil The Accuracy Requirement For The Definition Of The Itrfscale.