Exploring the Combination of VLF Transmitters and Lightning Emissions for D-region Ionosphere Remote Sensing

The D-region ionosphere (60-90 km in altitude) is critical for long-range communication; however, it is outside the altitudes reachable by both high altitude balloons and satellites making direct measurements of its electrical properties difficult. Instead, researchers have often relied on very low and low frequency (VLF, LF) radio waves, typically from either VLF transmitters or lightning, in combination with remote sensing techniques to infer properties such as electron density. While these two sources of VLF and LF radio waves provide different information, they have not been used together to form a single, cohesive model. In this work, we explore a tomography based approach to better understand how these two VLF sources can be used together and what limitations may exist. We also examine the differences in available information between the narrowband, but consistent VLF transmitters and the broadband, but sporadic lightning emissions.