Ionospheric Characterization Using VLF Whistlers

Abstract Broadband very low frequency (VLF, 3–30 kHz) energy emitted from lightning travels long distances in subionospheric propagation modes. Some of this energy couples into the ionosphere and travels to satellite altitudes along a predominantly field‐aligned path in what is known as a “whistler” propagation mode. Along this path, these VLF signals (known as whistlers) encounter both frequency‐dependent absorption and dispersion. When observed by satellites, these signals can be used to estimate the electron density profile along the path from the whistler to the satellite. A new technique for estimating electron density profiles in both the lower and upper regions of the ionosphere is presented using trans‐ionospheric VLF whistlers recorded by the DEMETER satellite. This technique employs an inverse modeling‐based approach to select a parameterized model of electron densities in the D‐region (60–90 km), as well as a scaling term that can be applied to the electron density profiles provided by the International Reference Ionosphere (IRI) for altitudes above the D‐region (90–700 km). Leveraging a set of 52 whistlers recorded by the DEMETER satellite in 2010, the algorithm produced consistent estimates for parameters representing the altitude and sharpness of the D‐region, as well as the altitude and thickness of an often‐occurring shelf in the D‐region, all of which are in alignment with known values for these parameters. Additionally, the algorithm produced a consistent scaling term for the IRI model of the E and F regions for the 52 recorded whistlers, with a mean value of 0.507 and a variance of only 0.009.