Lightning Geo-location via Combined use of Time of Arrival, Arrival Azimuth, and VLF Dispersion Measurements of Radio Atmospherics

Every lightning strike generates a strong electromagnetic pulse with a high spectral content at very low frequencies (3-30 kHz). Those strikes with a large vertical discharge component launch a Very Low Frequency (VLF) wave that efficiently propagates through the earth-ionosphere waveguide. The horizontal component of the magnetic field from this VLF radio impulse can be recorded using two orthogonally oriented magnetic loop antennas. The geographic location of the lightning strike can then be determined by comparing arrival time differences from several such recording sites. The location accuracy of this technique depends linearly on the accuracy of the time of arrival estimation of the received waveform. Due to the dispersive nature of the earth- ionosphere waveguide, arrival time determination must take into consideration the propagation distance and path from the lightning strike to the receiver. This paper discusses new techniques for determination of the time of arrival of radio pulses generated by lightning strikes, with an emphasis on the use of the dispersive nature of the propagation path.