Evaluation of Spaceborne GPS Data Quality and Higher-order Ionospheric Delay Effects on SWARM Precise Orbit Determination in the Severe Geomagnetic Storm on April 23–24, 2023

Abstract

Geomagnetic storms significantly enhance ionospheric electron density, thereby severely influencing ionospheric delay and degrading the quality of spaceborne GPS observations for low Earth orbit satellites. Traditional study rarely focuses on precise orbit determination (POD) during geomagnetic storms using reduced dynamic method. To improve POD accuracy during Geomagnetic storm, this article proposes a new method applying higher order ionospheric (HOI) delay to correct onboard GPS observation using reduced dynamic method, exemplified by geomagnetic storm of April 23–24, 2023 for SWARM mission, characterized by heightened solar activity and increased geomagnetic indices. A comprehensive assessment of spaceborne GPS data quality reveals a marked deterioration in data quality with a close consistency with the geomagnetic indices. The HOI reaches centimeter level, with second-order ionospheric delays in the L1 and L2 bands peaking at 2.8 and 5.9 cm, respectively, and third-order delays reaching up to 0.7 and 1.8 cm. Overlap orbit validation shows that HOI delay correction can effectively improve the POD accuracy of the SWARM-A, B and C satellites. When HOI delay correction data are used in reduced-dynamic orbit determination, the resulting accuracy is higher than that achieved using ionosphere-free combination data, with an improvement on the order of millimeters. These results underscore the critical influence of HOI delay on onboard GPS observation during geomagnetic storms and highlight the necessity for accurate ionospheric modeling in enhancing POD accuracy.