Pure Geometrical Precise Orbit Determination of a LEO Based on GNSS Carrier Phase Observations

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Pure Geometrical Precise Orbit Determination of a LEO Based on GNSS Carrier Phase Observations

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Shabanloui, Akbar / Ilk, Karl Heinz

The interest in a precise orbit determination of Low Earth Orbiters (LEOs) especially in pure geometrical mode using GNSS observations has been grown rapidly. Conventional GNSS-based strategies rely on the GNSS observations from a terrestrial network of ground receivers (IGS network) as well as the GNSS receiver on-board LEO in double difference (DD) or in triple difference (TD) data processing modes. With the advent of precise orbit and clock products at centimeter level accuracy provided by the IGS centers, the two errors associated with broadcast orbits and clocks can be significantly reduced. Therefore, higher positioning accuracy can be expected even when only a single GNSS receiver is used as zero difference (ZD) procedure. In this paper, the zero difference procedure has been applied to CHAMP high-low SST observations then the solution denoted as Geometrical Precise Orbit Determination (GPOD). The determination of absolute positions based on only carrier phase observations has the disadvantage that the ambiguity term must be determined in addition, but the advantage with respect to the positioning accuracy is significant. The estimated geometrical orbit of CHAMP is point-wise and its accuracy relies on the geometrical status of the GNSS satellites and on the number of tracked GNSS satellites as well as on the GNSS measurement accuracy in the data processing. The position accuracy of 2-3 cm of CHAMP based on high-low GPS carrier phase observations with zero difference procedure has been realized. These point-wise absolute positions can be used to estimate kinematical orbit of the LEOs.