Next generation GNSS constellations for GGOS-compliant geodetic solutions (NextGNSS4GGOS)

• Applicant: Professorin Dr.-Ing. Susanne Glaser
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 451901242

The overall objective of NextGNSS4GGOS is to assess the benefits of next generation Global Navigation Satellite Systems (NextGNSS) constellations beyond current GPS, GLONASS, Galileo, or Beidou for geodetic solutions complying the requirements defined by the Global Geodetic Observing System (GGOS). A possible NextGNSS architecture “Kepler” proposed by the German Aerospace Center (DLR) consists of a Medium Earth Orbit (MEO) satellite constellation similar to Galileo, but with the unique features of perfect time synchronization and precise inter-satellite range observations via optical links. In addition, Kepler is characterized by a Low Earth Orbit (LEO) segment carrying ultra-stable optical clocks, connected with optical links for ranging and inter-plane clock synchronization. Other ideas for NextGNSS concern additional instruments onboard like inertial sensors, measurement of accelerations and rotations of the satellite, laser retroreflectors for Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) transmitters on the satellites. Within project NextGNSS4GGOS the potential of the new observation types will be investigated by comprehensive and most realistic simulations. A first important milestone will be assessing the impact on satellite orbits and clocks of a MEO constellation. In addition, the achievable orbit accuracies of a LEO gravity, altimetry, and radar imaging mission carrying NextGNSS receivers and new tracking devices (f.i. optical inter-satellite ranges between GNSS and LEOs) will be studied. Various scenarios augmenting a contemporary Galileo constellation will be simulated and compared to assess the individual and combined contribution of the new observation types. The second milestone will be the evaluation of the impact of the new observation types on the geodetic target parameters global terrestrial reference frames (TRFs), Earth orientation parameters (EOPs) and gravity field. Additional considerations such as a long-arc approach or the inclusion of LEO satellites to the MEO constellation are part of the research plan as well. At the end of the project we want to answer the question whether TRFs, EOPs, and gravity field models based on the envisaged NextGNSS will meet the GGOS requirements of 1 mm accuracy and 1 mm per decade long-term stability?

• DFG Programme: Research Grants