Formation of a GNSS network in space based on LEO satellites

The number of low Earth orbit (LEO) satellites equipped with Global Navigation Satellite System (GNSS) receivers is rapidly increasing. GNSS observations in space are no longer limited to a small number of Earth observation satellites, but large nanosatellite constellations enable the formation of a dense network of GNSS observations around the Earth. Such a space-based GNSS network holds great potential for geodetic Earth observation: First, it allows GNSS double-difference processing in space, where GNSS signals are not affected by tropospheric refraction and where no ground observations are needed. Second, a dense and homogeneous GNSS network in space may improve the sensitivity to certain geodetic parameters by providing a better observation geometry than a few LEO satellites or a ground-based network.In this study, we investigate the feasibility of forming a space-based GNSS network for estimating orbit parameters of LEO and GNSS satellites, as well as low-degree coefficients of the Earth’s gravity field. We therefore process three different datasets: (1) simulated GNSS observations for potential LEO-constellation scenarios; (2) GNSS observations from a pseudo-constellation consisting of existing geodetic Earth observation missions, including GRACE, OSTM/Jason-2 and the Sentinel satellites; (3) GNSS observations from a nanosatellite constellation.We examine the sensitivity of estimated parameters to small errors in the observation data resulting, e.g., from the force model. Furthermore, we analyse how well carrier-phase ambiguities can be resolved and how this depends on the constellation configuration. This allows us to draw conclusions about the potential of large satellite constellations to complement the existing geodetic Earth observation missions.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)