Broad band radio interferometry for lightning observations

Abstract

A broad band radio interferometer for locating lightning emissions has been designed, constructed and tested. For a broad band interferometer, a single fixed pair of antennas is equivalent to having many baselines in a narrow band interferometer. So, a broad band system requires fewer antennas than a narrow band system to achieve equivalent angular resolution. In addition, frequency dependent locations of the radio emissions can be extracted for a more detailed look at the lightning breakdown processes. Such a system has been tested by a computer simulation and by measuring a man‐made broad band radiation source. The system consists of two antennas which are separated vertically. Bandwidth of the system is from 40 to 350 MHz. Measurements of the man‐made source indicate that with a signal‐to‐noise ratio (SNR) above 10 dB, the system is able to locate the source with an accuracy of about 2° over the detectable frequencies. Preliminary observations of lightning discharges with this new technique appear to indicate that breakdown processes of a dart leader to ground radiate solely at its descending tip.