Using lightning as a HF signal source to produce ionograms

Modern techniques for specifying the ionosphere include the use of ionosondes, which both transmit and receive sweep soundings in the high-frequency (HF) band. We replicate this process by observing the broad band emission from lightning using the Long Wavelength Array, Sevilleta, radio telescope. We use this station to observe the powerful broadband radio bursts from the breakdown of air that occurs during lightning flashes. For nearby lightning we observe both the direct line of sight and the delayed ionospheric reflection. By correlating the amplitude time series from the direct line of sight to that of the ionospheric reflection, we can accurately measure the group delay as a function of frequency. By separating into right-hand circular and left-hand circular, we can derive both the O mode and X mode ionograms. This novel technique allows for accurate ionograms to be made even in restricted frequency bands and provides a means to probe density profiles at multiple locations of the ionosphere on short time scales with a single receiver station.