Single station lightning location using azimuth and time of arrival of sferics

Lightning strikes produce electromagnetic waves, now referred to as sferics, in the very low frequency (3 kHz–30 kHz) and the extremely low frequency (3 Hz–3 kHz) bands. Within these frequency bands, the Earth and ionosphere form a waveguide in which sferics propagate long distances with low attenuation. The structure of the received sferic waveform is mainly a function of propagation distance and the waveguide's parameters. This suggests that each observed sferic waveform contains information about the distance that this sferic has propagated which can be used to geolocate lightning. There are various approaches for analyzing received sferics, which mostly rely on measurements from multiple stations. However, in these methods, each station imposes an additional cost for building, maintenance, and synchronization. Here we present a novel method to estimate both the emission time and location of lightning, which works by measuring sferics recorded at a single station. We first process the sferic waveforms to obtain the arrival times of the very low frequency and extremely low frequency radiation components which propagate with different speeds. Once these two separate arrival times are determined, we use them to approximate the distance the sferic propagated in the Earth-ionosphere waveguide. We have used this novel method in combination with a method to find sferic direction to geolocate a significant number of lightning strikes for 4 July 2013. Using this proposed method, the distance of propagation estimates are accurate to within 6.7% of the National Lightning Detection Network-determined propagation distance, and the direction of propagation estimates are accurate to within ∼ 1.3% of the National Lightning Detection Network-determined direction.