Workshop 2018
Dmitry Sidorov - Improved orbit modelling of Galileo satellites during eclipse seasons - October 29, 2018 • 597 Views
In 2012 the Center for Orbit Determination in Europe (CODE) joined the Multi-GNSS-EXtension project (MGEX) of the International GNSS Service (IGS). Since the end of 2013 the CODE MGEX contributions were based on combined solutions of five already established and emerging GNSS: GPS, GLONASS, Galileo, Beidou and QZSS. This undertaking was made possible thanks to the continuous development of new models and approaches and their introduction in our processing schemes in order to ensure the delivery of products of the highest quality. The European Galileo system is currently the third largest GNSS after GPS and GLONASS with a total number of active satellites exceeding 20. Because of their low weight the Galileo satellites are more sensitive to non-gravitational forces than other GNSS satellites. The introduction of the extended empirical CODE model (ECOM2) to the CODE MGEX solutions in early 2015 resulted in a significant improvement of the Galileo products. The use of the Galileo satellites metadata, which were made public in the course of 2016 and 2017, has further enhanced the quality of the produced solutions. However, they still show significant degradations during eclipse seasons in particular for long-arc solutions (e.g., over three days), which are similarly observed in solutions of other IGS MGEX analysis centers to different extents. In particular this is reflected in elevated orbit misclosures at day boundaries, deterioration of satellite clocks and excessive Satellite Laser Ranging (SLR) residuals during these periods. Since the ECOM2 parameters are designed to absorb the effect of solar radiation pressure, they are switched off during eclipses. Hence, there is no empirical force parameter left that can absorb any unmodelled perturbations (e.g., due to thermal radiation (TR)) during an eclipse period. In this study we advance our orbit model further by introducing empirical parameters to account for unmodelled perturbations acting on Galileo satellites, e.g., TR effects while the satellites pass the Earth’s shadow. The presented results include the assessment of the benefits of significantly improved modelling on both IOV and FOC satellites with a focus on eclipse seasons.

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