Broadband VHF Localization of Lightning Radiation Sources by EMTR

In this paper, a novel mapping algorithm by applying electromagnetic time reversal (EMTR) technique to broadband very high frequency (VHF) for the direction-of-arrival (DOA) estimation of lightning radiation sources is proposed and validated. Based on the theory of array signal DOA estimation and time reversal (TR) principle, the lightning radiation receiving model with broadband VHF array is established, and thereafter the TR synthesized signal for arbitrary direction is derived. It is proved that the direction with the maximum norm of synthesized signal is the optimal estimation for the incident direction, and hence the procedure for the EMTR-VHF method is derived. Numerical simulations are conducted for testing the algorithm and investigating the relationships between the array spatial resolution and the available signal frequencies, robustness of the algorithm, et al. Two metrics, amplitude ratio and energy ratio, are devised to filter false locations, and the acceptable ranges of them are further estimated by simulation. In order to further validate the EMTR-VHF algorithm, field experiments are carried out. The results show that the EMTR-VHF method performs well, especially for the sources with low elevations, with the error less than 1°. Finally, the application of EMTR-VHF method in locating a negative cloud-to-ground flash is presented. Temporal and spatial development of the leader-return stroke sequence could be well depicted. The results are generally consistent with the VHF interferometry technique, which confirm its ability in lightning localization. Besides, the discrepancy between this algorithm and broadband interferometry method are documented.