Patent ID: 10983231

Abstract:
A computer calculates a change amount of a total number of electrons from an observation start time in the ionosphere between an observation station and a satellite based on observation data of a signal received from the satellite by the observation station on the ground. The computer estimates the change amount of the total number of electrons to be calculated next based on the time change of the change amount of the total number of electrons from the observation start time in the ionosphere and calculates a difference (estimation error) between the estimated change amount of the total number of electrons and the actually calculated change amount of the total number of electrons. The computer calculates a correlation value between the estimation error calculated for each observation station and the estimation error calculated for a predetermined number of the observation stations in the vicinity of each observation station. In a case where the correlation value calculated for each observation station is a predetermined threshold value or more, when the correlation value is also the predetermined threshold value or more for the predetermined number of observation stations in the vicinity of the observation station, the computer determines that an abnormality has occurred in the ionosphere between the observation station and the satellite.