Delay Correction Method Based on VLF Timing Signal Phase Variation Model.

Area of Science:

• Geophysics
• Signal Processing
• Navigation Systems

Background:

• Satellite-based positioning, navigation, and timing (PNT) services face challenges like signal interference and limited availability.
• Very-low-frequency (VLF) signals offer a terrestrial alternative for time transfer but are susceptible to propagation-delay variations, particularly diurnal changes.

Purpose of the Study:

• To develop and evaluate a propagation-delay correction method for VLF timing signals.
• To mitigate the impact of ionospheric diurnal variations on VLF signal timing accuracy.

Main Methods:

• A phase-variation model was developed to correct VLF timing signals.
• Total delay error was separated into primary path delay, secondary propagation delay, and residual error.
• Periodic secondary delays were corrected using predicted phase variation from historical Alpha observations.

Main Results:

• The proposed method reduced the standard deviation of timing errors for Chongqing paths to 2.0054-2.2500 μs and for Guilin paths to 2.7987-4.4792 μs.
• The corrected root mean square error (RMSE) ranged from 2.1316 μs to 4.5641 μs across six Alpha propagation paths.
• The method effectively suppressed the main diurnal propagation-delay component in the analyzed VLF datasets.

Conclusions:

• The developed propagation-delay correction method shows promise for improving the stability of VLF timing signals.
• The findings suggest that VLF signals can serve as a more reliable terrestrial complement to satellite-based PNT systems.
• Further validation with contemporary and multi-season VLF observations is recommended.