Ambient VLF Transmitter Variation Detected at Many Locations

Abstract:

Very Low Frequency (3-30 kHz) and Low Frequency (30-300 kHz) radio transmitters are an important means for naval submarine communications. VLF waves travel through the Earth-ionosphere waveguide with low attenuation and penetrate into conducting seawater. These transmitters also serve as a useful diagnostic tool for characterizing the D region of the ionosphere, a region of the ionosphere that is inaccessible to continuous in situ measurement techniques.

The temporal variation of these VLF signals are dominated by ionospheric conditions, and their response to localized or global disturbances. However, despite extensive past work on the analysis of these diagnostic signals, little is known about the spatial relationship between ionospheric conditions at multiple locations. We utilize a previously erected global constellation of transmitters and receivers to determine generalized characteristics and trends for ambient daytime conditions of the lower ionosphere. We present the data and analyze them to reveal trends in the amplitude of these transmitters, in an effort to better characterize the ambient ionospheric conditions and their spatial variations on a global scale.