Estimation of Return Stroke Velocity by Time‐Reversal Reconstruction of Channel Feature Points

Abstract

In order to better understand the process of the return stroke (RS), based on the time‐reversal (TR) method, the feature points in the fine structure of the RS electric field (E‐field) waveforms are mapped to the feature points in the RS channel, and velocity of the RS is calculated. First, by using the RS engineering model of the tortuous channel with variable velocity, it is shown that the fluctuation of RS velocity and the tortuous channel will lead to subsidiary peaks of the E‐field waveform in the LF band, the variation in the width of the subsidiary peak is correlated to the scale of the segmented tortuous channel and the variation of the velocity, and the contributions of the radiation field to the subsidiary peaks on the total field are the largest. Then, simulation examples under conditions of vertical, inclined, and tortuous channels are used for validation. Combined with the TR approach, the time‐reversed E‐field waveforms are back‐propagated and superimposed, the focused points are in good agreement with feature points in the RS channel. Finally, the reconstruction results of the feature points in the RS channel of a natural negative cloud‐to‐ground lightning are presented, and the average velocity between the feature points is calculated, which falls in a reasonable region between 0.35 × 108 and 1.73 × 108 m/s.