Correcting geocenter motion in GNSS solutions by combining with satellite laser ranging data

Abstract Geocenter motion in GNSS solutions is ill-defined because of the GNSS orbit modeling errors. Especially, the Z geocenter component derived from GNSS data is mostly affected, as that includes strong draconitic signals. In GNSS processing, we lack direct access to Earth’s actual center of mass, even though orbital dynamics fundamentally depend on it. Instead, satellites are computed to orbit around a theoretical point that has no geophysical interpretation, called the apparent center of mass. We derive a method of enhancing GNSS processing by incorporating the correct geocenter motion information by combining GNSS microwave-based observations with Satellite Laser Ranging (SLR) observations to Galileo and GLONASS, as well as SLR observations to two LAGEOS satellites. We found that SLR observations to GNSS cannot improve the geocenter variations alone because GNSS solutions are still affected by spurious draconitic signals. Oppositely, SLR observations to LAGEOS almost eliminate the draconitic signal in the Z geocenter component and guarantee that the geocenter motion is properly handled in the GNSS processing. To achieve this, adding range observations to LAGEOS is sufficient, even without considering SLR observations to GNSS satellites, thus, even without the proper SLR-GNSS co-location in space onboard GNSS satellites. We also found that different handling of range biases in SLR data to GNSS may change the mean geocenter offset, however, it does not have any impact on the geocenter temporal variations and reduction of the draconite signals.