Studying the Fixing Rate of GPS PPP Ambiguity Resolution Under Different Geomagnetic Storm Intensities

Global Positioning System (GPS) Precise Point Positioning (PPP) with correct fixing ambiguity resolution (AR) can reach cm-mm level positioning accuracy. However, this accuracy can be degraded by the geomagnetic storm effects. To comprehensively investigate the ambiguity resolved percentage (ARP) of GPS kinematic PPP, referred to as PPP-ARP, under different intensities of geomagnetic storms, based on the Natural Resources Canada's Canadian Spatial Reference System (CSRS) PPP, this study for the first time gives the correlation between the PPP-ARP and storm intensity using 67 storms occurred in the past 5 years of 2018-2022. Experimental results indicate that the PPP-ARP decreases gradually as the increase of geomagnetic storm intensity. Under quiet and low geomagnetic conditions (Dst(min) > -50 nT), the PPP-ARP of global GNSS stations can achieve more than 96%, while these during strong storms (Dst(min) <= -100 nT) are generally lower than 90.0%, especially for the PPP-ARP of some stations located at low latitudes which are lower than 40.0%. The mechanism of PPP-ARP decrease under geomagnetic storms is mainly due to the cycle slips and even loss of lock of GNSS signals caused by the storms induced ionospheric disturbances and scintillations. In addition, different from many previous studies, we found that the CSRS-PPP with AR can achieve good positioning accuracy (3D RMS <0.2 m) even under strong geomagnetic storms.