Automatic System for Global Monitoring of ELF and VLF Radio Noise Phenomena

摘要

A new system has been developed for automatically monitoring and recording electromagnetic noise in the ELF and VLF (10-32,000 Hz) frequency band. Eight stations are under construction, to be installed at different sites around the world in order to map the geographic distribution of noise levels. This system is called the ELF/VLF Radiometer to emphasize the attention paid during its design and installation to making accurate absolute field strength measurements. The sensing instruments installed at each site consist of two dual-channel receivers, each with two crossed loop antennas. The ELF receiver covers the frequency range 10 to 500 Hz, and the VLF receiver the range 300 to 32,000 Hz. A bank of 16 narrowband (5% bandwidth) filters is used to monitor the energy present at selected frequencies throughout the range of both receivers. The output of these filters is continuously sampled by a computerized recording system, and statistical averages are computed on-site and recorded on digital tape, along with a sample of the raw digital data. Broadband samples of both receivers are taken periodically to provide a check on system performance and to aid in interpretation of the statistical data. Also recorded on digital tape are system status and gain information, as well as messages entered by the operator.