Research progress on correction of radio wave propagation errors in land-based low-frequency navigation and timing systems

Enhanced Long-Range Navigation (eLoran) has significant supplementary and backup value in global navigation satellite systems under conditions of interference, spoofing, or denial, but due to its signal propagation process being affected by spatial physical environmental factors, it produces deviations in propagation delay from ideal paths, which in turn leads to calculation errors in receiving systems, severely limiting the improvement of system accuracy. The article first systematically elaborates on the relevant definitions, fundamental theories, model methods, and research progress of electromagnetic wave propagation error correction in low-frequency navigation and timing systems. On this basis, it summarizes the current research status in five aspects of electromagnetic field numerical calculation, low-ionosphere modeling, regional correction and differential enhancement, intelligent prediction, and additional secondary factor (ASF) experimental measurements in electromagnetic wave propagation error correction. Overall, electromagnetic wave propagation error correction has gradually evolved from single-path, static compensation to a dynamic and intelligent correction system oriented towards complex environments and regional service needs. Finally, it clarifies the current challenges and future development directions regarding the joint application of sky waves and ground waves.