Evaluation of Height Correction on Loran Signal's Groundwave Transmission Delay Model

With the ongoing construction and development of the enhanced long-range navigation (eLoran) system, people's needs for the accuracy of positioning navigation and timing (PNT) service provided by the Loran system are increasing. Due to the high altitude at which the new eLoran transmit station will be constructed, the effects of elevation cannot be discounted. Since the existing Loran propagation model has not systematically taken the impact of elevation into account, new factors have to be added to existing model for users at high-altitude areas. In this letter, the groundwave transmission delay model's height correction factor is provided. Also, by using a modified ellipsoid expansion technique, it is possible to investigate the impact of elevation on the calculation of geodetic line length, a crucial step in the PNT solution of the Loran system. The findings indicate that, in comparison to the built-in algorithm of the current receiver, taking elevation into consideration will result in unavoidable correction for users who are 250 km or less from the transmitter or for users who are more than 500 km away.