Ionospheric Threat Model Assessment

Abstract

This paper presents the first results of a German study (ITMA) that attempts to validate the GBAS CAT I ionosphere threat space that was developed for US CONUS. In phase 1 of this study the German Aerospace Center DLR and the German Air Navigation Service Provider DFS tried to determine the normal residual ionospheric uncertainty (σvig) and to identify periods with severe ionospheric activities relevant for GBAS. Dual-frequency RINEX data of up to 80 geodetic stations in and around Germany over an 11 year solar cycle from 1998 (25 stations) to 2008 (80 stations) was processed. Based on this data evaluation the study determined 16 periods with disturbed ionosphere in the years 2000 to 2003 and one day in 2005. These periods will be analyzed in more detail in phase 2 of the study to populate the GBAS CAT I ionosphere threat space. To determine the necessary parameters slope, velocity and width of the identified ionospheric fronts it is necessary to use additional GNSS data from German geodetic networks. This additional data should improve the resolution in the areas where the ionospheric front was detected. Phase 2 of the study should be completed in autumn 2009. The database may then be used to validate the assumptions regarding ionospheric effects for GAST-D.