Example of a solar radio burst impacting the GPS service at the L2 frequency. Top panel: Solar radio burst on 24 September 2011 observed at 1.4 GHz by the RSTN station LISS. Second panel from the top: Signal strength degradation at the IGS station MAS1. The figure is the result of subtracting undisturbed reference observations from the reported signal strength of the satellites during the solar radio burst. Third panel from the top: Reduction in the number of available satellites at station MAS1 compared to undisturbed conditions. The severity of the reduction at each instant is color-coded and indicated at the bottom of the panel. The classification in levels of degradation is the same as in Figures 2 and 3, as detailed in the text. A signal strength mask of 24 dBHz is used. Bottom panel: Same as the third panel but for the geometric dilution of precision. The gaps indicate a period of time when the system failed to meet minimum operational requirements.