Time-Frequency Analysis of Ionosphere Disturbances by Using Variational Mode Decomposition

Abstract

Ionosphere has several effects on radio signals. Traveling wave-like ionospheric disturbances can occur due to solar radiations, seismic activities. Receiver loss of locks and some positioning errors can occur because of these disturbances. The time frequency structure of ionosphere has to be determined in order to detect this kind of disturbances. Slant Total Electron Content (STEC) is a metric that characterize the ionosphere and defined as the line integral of electron density on a ray path from satellite to receiver. In this study, variational mode decomposition method is applied on STEC values to understand the time frequency behavior for disturbances for the first time. Daily STEC values are decomposed into its components in time and frequency domain by using VMD method. By the help of this method, periodic structures of ionospheric disturbances are determined. The behavior of the disturbances varies with the satellite direction and both in time and frequency domain. Probability density functions of frequencies in West and North directions are similar whereas probability density function computed in east direction differs from other direction over Turkey.