Noise Assessment and Mitigation for Loran for Aviation

The United States released the technical report on the ability of Loran to mitigate the effects of a GPS outage in December 2004. The report indicated that the current Loran system, with reasonable upgrades and modifications, could provide backup to GPS for aviation, maritime and timing users. The conclusion was based on the results of the analysis of many significant hazards to Loran usage. One critical factor is atmospheric noise, particular at extreme conditions. Atmospheric noise results from lightning discharge and as such, it can vary greatly from moment to moment. High levels of atmospheric noise, above the 95 percentile, are of great concern. The International Radio Consultative Committee (CCIR) noise model indicates some extremely high values for high levels of atmospheric noise. While these values still generally result in acceptable availability of the Loran system for aviation, actual performance is suspected to be better. This is because the CCIR data collection equipment differed substantially from those of a typical Loran receiver. Hence, it is necessary to conduct data collection to supplement the knowledge found in CCIR. A data collection system was developed to collect atmospheric noise data. Data were collected at two areas of known high atmospheric noise Socorro, NM, and Minneapolis, MN during the summer of 2004. Further data collection will be conducted in 2005. The data were first used to assess the reasonableness of the CCIR noise values. An additional use will be to refine the CCIR noise model for the Loran band. This will include developing a statistical model for lightning. In addition to studying the noise, its statistics, and characteristics, it is also important to understand how to mitigate its effects. This paper discusses the data collection set up and presents the preliminary analysis of the data collected at various sites.