In order to locate the faint sources in the lightning discharge, an improved broadband VHF observation system is developed. Both the system configuration and locating algorithm are specially designed to locate weak radiation sources from background noise. The proposed system consists of seven broadband omnidirectional antennas in “L”shape and runs in continuous acquisition mode. An electromagnetic time reversal method designed in frequency domain is applied to locate the radiation sources. Two metrics have been introduced to distinguish between actual lightning sources and noise event. Numerical simulations and field calibration are carried out to test the system's performance in locating weak sources. Moreover, the performance on spatial resolution, robustness, and the ability of multi-source localization are investigated. Finally, this system is applied to map the propagation of the upward positive leader (UPL) from a classical triggered lightning with time resolution 0.128 μs. The results prove that the proposed system could well depict the whole progression of UPL until its extinction, and the advantages of the proposed seven antennas array in retrieving weak radiations are presented in detail.

The characteristics of two natural positive cloud‐to‐ground flashes are analyzed in detail with the broadband very high frequency (VHF) mapping system. The bidirectional leader processes at the lightning initiation are observed, with negative leaders propagating upward and positive leaders propagating downward. The downward positive leaders can be divided into two stages, with scattered and slowly extending sources in the first stage and more concentrated and faster sources in the second stage. The overall extension speeds of the first stages are 1.8 × 10⁴ and 2.7 × 10⁴ m/s for the two flashes, and the speeds of the second stages are 7.8 × 10⁵ and 1.0 × 10⁶ m/s, respectively. The received peak power of the positive leaders is substantially lower than that for the negative leaders. The frequency characteristics show that the second stage emits more high‐frequency radiation than the first stage, while there is no significant difference in low‐frequency radiation content.

VHF (Very High Frequency) lightning interferometers can locate and observe lightning discharges with a high time resolution. Especially the appearance of continuous interferometers makes the 2-D location of interferometers further improve in time resolution and completeness. However, there is uncertainty in the conclusion obtained by simply analyzing the 2-D locating information. Without the support of other 3-D total lightning locating networks, the 2-station interferometer becomes an option to obtain 3-D information. This paper introduces a 3-D lightning location method of a 2-station broadband interferometer, which uses the theodolite wind measurement method for reference, and gives the simulation results of the location accuracy. Finally, using the multi-baseline continuous 2-D locating method and the 3-D locating method, the locating results of one intra-cloud flash and the statistical results of the initiation heights of 61 cloud-to-ground flashes and 80 intra-cloud flashes are given. The results show that the two-station interferometer has high observation accuracy on both sides of the connection between the two sites. The locating accuracy will deteriorate as the distance between the radiation source and the two stations increases or the height decreases. The actual locating results are similar to those of the existing VHF TDOA (Time Difference of Arrival) lightning locating network.

A low-frequency lightning location system was established and operated. The time-reversal approach in the frequency domain (TRFD) is applied to the system for three-dimensional (3-D) lightning source location finding. The TRFD method uses back propagation of the signals detected at each site and determines the source location automatically using the focusing point of the back-propagated waves. Three cases are reported to showcase the capability of the method. The first case is the 3-D localization of an intra-cloud flash over the network. Both TRFD and time-of-arrival (TOA) method provide LF lightning sources that are in consistent with very high frequency (VHF) sources. The lightning sources located by TRFD method reveal more details and are more continuous compared to those obtained by TOA method used in this paper. The second case concerns the localization of an artificially triggered lightning flash with a horizontal error of 30 m by TRFD. The third case is a multi-stroke cloud-to-ground flash that shows location differences between four return strokes (RSs) being less than 60 m. Furthermore, a special case was used to demonstrate the ability of the proposed method in locating RS grounding points by combining two successive RSs when the TOA is not available.

Waveform cross‐correlation approach was first applied to three‐dimensional very high frequency (VHF) lightning mapping. A Hilbert transform of the original waveform and a three‐step cross‐correlation parsing process were employed to compute the time differences with a small 10‐μs time window for the final time‐of‐arrival (TOA) positioning. The lightning channel continuity was significantly improved, and its fine structure, including the K process, was clearly distinguished with speeds of up to 1.1 × 10⁷ m/s. The two overlapped K processes indicate the high location accuracy of the time‐of‐arrival, based on the waveform correlation method. The median (mean) values of the positioning precision with the proposed method were evaluated by duplicate located sources and estimated as σ_x = 20 m (26 m), σ_y = 19 m (28 m), and σ_z = 54 m (67 m).