Worldwide monitoring of VLF-LF propagation and atmospheric noise

A joint effort is underway between The Johns Hopkins University Applied Physics Laboratory and the Space and Naval Warfare (SPAWAR) Systems Center. San Diego, to deploy monitoring equipment capable of characterizing worldwide VLF-LF radio wave propagation and atmospheric noise levels. The monitoring equipment consists of a PC-based spectrum analyzer and orthogonal ferrite core magnetic loop antennas. The analyzer performs continuous measurements of the radio spectrum from 12 to 62 kHz and records time histories of VLF-LF signals (equivalent vertical electric field strength), noise amplitude probability distribution, noise impulsiveness, and average noise field strength. Data are downloaded via the Internet to a central database server. The Internet connection also provides for system reconfiguration and clock synchronization. Data collected by the monitoring network will be used to improve communication coverage forecasts and to analyze transient and long-term propagation effects. This paper provides an overview of the monitoring network and samples of data collected by it.