Lightning VHF Radiation Mapping Method for an Irregular Short-Baseline Array

Lightning very high frequency interferometry is a crucial tool for studying the development of lightning leaders within thunderclouds, and the conventional antenna array is composed of two coplanar orthogonal baselines. In this study, we develop two new location methods for an irregular array based on the optimization algorithm, using all baselines in the calculation. Besides, we have analyzed the effects of two kinds of time uncertainty on the location result and provided a calibration method. The first type-the systematic time drift of antennas-can induce an offset on the location result, leading to a worse accuracy. We can calibrate the time drift of each antenna efficiently during the experiment. The second type-the waveform distortion between different antennas-can introduce the noise on time, leading to worse precision. The location precision improves when more baselines are used, whether they are independent or redundant. Our result shows that the non-coplanar configuration can significantly improve the elevation uncertainty near the horizon and the azimuth uncertainty near the zenith after considering the angular uncertainty's theoretical distribution.Plain Language Summary Lightning discharge emits abundant very high frequency (VHF) radiations, for which the clouds are nearly transparent. The technology of detecting and locating the radio emission makes it possible to know how lightning leaders propagated inside the thunderstorm. The broadband VHF interferometry is a widely used detection system, which consists of at least three antennas with a distance between antennas (baseline) of several to tens of meters. Typically, these antennas are deployed in the horizontal plane as an isosceles right angle. Considering the lightning is tens of km away from the antenna, we usually assume the VHF radiations generated by lightning as plane waves. A conventional method uses two orthogonal baselines to obtain radiations' arrival direction, which has low accuracy for elevation near the horizon and low accuracy for azimuth at the zenith. In this study, we develop a technique for an irregular array where antennas are non-coplanar and show that the non-coplanar configuration and more baselines could lead to higher accuracy and precision location results.