Airborne Measurement of Low Frequency Atmospheric Noise ALFAN I

Abstract : Essential airborne VLF/LF communication systems use long-wire transmitting antennas trailed behind high-flying aircraft. RF energy with a transverse magnetic polarization radiated by these antennas has been used in long-range communications. Recently, airborne systems have been upgraded and can receive transverse electric polarized waves. The range and connectivity of these communication systems are based on predictions from computer codes. Levels of atmospheric noise at aircraft altitude are predicted from models of lightning and ground-based measurements. Recent information on the amount of cloud-to- cloud lightning indicates the possibility that airborne noise level predictions may need to be revised. RADC Project ALFAN was devised to measure atmospheric noise from a balloon-borne antenna/receiver system. In this report, the system and first flight are described. Initial results are presented and discussed in terms of their possible implications for communication systems. Keywords: Electromagnetic wave propagation; Very low frequency; Low frequency; Aircraft antennas; Trailing wire antennas; ALFAN(Airborne Low Frequency Atmospheric Noise).