An evaluation of eloran as a backup navigation sensor for ADS-B

Document Type

Conference Proceeding

Date of Original Version



The concept of Automatic Dependent Surveillance -Broadcast (ADS-B) is a paradigm shift for the way aircraft tracking is done in the National airspace. Currently tracking is done by systems of ground-based radars and other surveillance systems that measure the position of the aircraft and identify them based on radar transponders and IFF systems. In ADS-B, each aircraft determines its own position using an accurate position sensor and reports its identity, position and velocity over a communications link. This system has the potential to increase airport and airspace capacity while also improving safety. The key to ADS-B is that the aircraft must have an accurate position sensor. The primary sensor for this purpose is presumed to be GPS; however, a back-up system must be available in case of GPS outages. Loran has already been shown to be the ideal back-up system to GPS due to its orthogonal failure modes. The question is can it be used as a positioning source for ADS-B? In this paper we will evaluate the suitability of Loran as a backup positioning source. A significant factor limiting the accuracy of the Loran system is the variation in the times of arrival observed by the receiver due to the signals propagating over paths of varying conductivity, so-called the additional secondary factor (ASF). The current approach to Loran navigation in the harbor entrance and approach (maritime) environment is to establish a spatial grid of ASF corrections covering the area of interest. To extend this concept to ADS-B, such a grid of ASF values fully covering CONUS is needed. In this paper we will examine the position performance achievable using predicted ASF grids from the BALOR software.

Publication Title

Proceedings of the Institute of Navigation, National Technical Meeting



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