Loran-C Ground Wave Transmission Path Correction for High Elevation Based on the Huygens–Fresnel Principle

Conventional Loran-C is mainly used for low-altitude users; however, when the Loran-C signal station or receiving point is at a higher altitude, the ranging error caused by the elevation change cannot be ignored. The traditional groundwave path correction method for high altitude regions idealises the complex groundwave path as a smooth, extensive elliptic line. However, this is a rough and inaccurate correction value $\left(\Delta S\right)$ for the groundwave path. In this paper, based on the Huygens–Fresnel principle, we analyse the Loran-C groundwave path, and propose the Groundwave path accumulation (GPA) method, which calculates the complex terrain groundwave transmission paths in segments, to solve the problem of the low accuracy of $\Delta S$ in the traditional method. With the opening of high-altitude Loran-C stations in western China, the algorithm in this paper can improve the accuracy of Loran-C users' packet positioning to a certain extent in central and western China, Central Asia, and South Asia. The article analyses the correction value of the GPA algorithm to the Loran-C ground wave transmission distance between two points with elevation, and the ground wave path correction value is 46.918 m in the elevation difference of 2500.000 m and no elevation distance of 414,306.538 m.