Example of the output plot from the EPB detection method obtained at the Arequipa (areq) receiver in communication with satellite PRN 4 on February 26, 2014. The top panel shows the TEC computed from the code delays (PI) in blue, the TEC obtained from the carrier-phase delays (LI) in red, and the fitted background TEC, TEC₀ during the EPB duration in green. The second panel shows the disturbance ΔTEC(t) in green and the significance threshold for the depth set at −5 TECU in the orange horizontal line. The third panel shows the evolution of the standard deviation of the TEC (in LI) second derivative, σ(TEC″(t)), in red, and the orange horizontal line at 0.714 TECU corresponds to the threshold used to determine the EPB initial and final times T_i and T_f. EPB initial and final times T_i and T_f are indicated by orange vertical lines in all the panels.