Chronos has participated in the ESA funded project UK Time Distribution.
The goal of the project was to measure and model Additional Secondary Factors (ASF) for eLoran signal propagation over land. The precision of the received eLoran signal is dependent upon the signal delay that the ground introduces, therefore it is important to quantify the ASF to ensure the resilient eLoran time signal can meet the needs of Critical National Infrastructure (CNI).
The vulnerability of GNSS signals reception to natural and man-made interference is well known. eLoran is a terrestrial system that broadcasts high power 100kHz signals and does not share the same vulnerabilities as GNSS.
The project addressed the longer-term objectives of strategic PNT Resilience to support Critical National Infrastructure. In 2023, the UK Government published a 10-point plan outlining the framework for greater PNT resilience and the development of eLoran as a backup timing system is point number 5. At present there is one operational eLoran station in Anthorn, UK, which broadcasts signals suitable for timing. In future, further stations are planned for deployment in UK territories, which will enable positioning as well as timing.
During the activity, Chronos replaced the caesium atomic clocks which provide a stable time reference for the Anthorn transmitter. ASF measuring systems based on eLoran receivers were developed and installed at >10 locations across the UK – in addition one receiver was installed at ESTEC. ASF data and timing data was collected for >12 months because ASF varies according to several factors such as weather conditions. The ASF was also modelled and compared with the collected data. Chronos is continuing to collect data and improve our model of the ASF, which could be included inside eLoran receiver developments in future to improve the precision of the signal.
This project was funded through ESA’s NAVISP Element 3, targeting support to Member States in PNT.
Chronos presented the results of the ESA funded project UK Time Distribution on 27 June 2025. View the presentation here.
