Combined Orbit Determination Based on Carrier-Range observation

In recent years, an increasing number of Low-Earth-Orbit (LEO) satellites have been launched into space, some of which carry at least one onboard GNSS receiver. The combined orbit determination of LEO and GNSS satellites, utilizing onboard GNSS receivers and ground GNSS stations, is of great significance for improving the geometric observation configuration of GNSS satellites and enhancing the accuracy of satellite orbit determination. The aim of this study is to address the key issues in the integration of onboard GNSS observations from LEO satellites and ground-based GNSS observations. Our primary objectives includes exploring methods for fixing single station ambiguity based on integer clocks and subsequently forming carrier range observations, which is the basis of our study on combined orbit determination; establishing a proper stochastic model for integrating onboard GNSS observations with ground-based GNSS observations, by utilizing the variance component estimation; evaluating effects of different narrow lane UPD estimation strategies on the fixed ambiguity rate and orbit determination accuracy, offering an estimation strategies which could balance computational efficiency and accuracy of orbit determination better. Data from LEO satellites such as GRACE-FO, Swarm, Sentinel-6A and data from IGS network are processed in our study for evaluating different strategies and validating our conclusion.