A novel atmospheric-delay correction technique for enhancing satellite–ground two-way time synchronization

Abstract High-precision time synchronization is a core technical challenge in modern space science, deep space exploration, and time–frequency metrology. Traditional microwave links struggle to achieve picosecond-level synchronization due to atmospheric delays (tropospheric and ionospheric effects). We propose a novel atmospheric delay correction technique using a triple-frequency microwave link that enables the simultaneous cancellation of atmospheric errors. This technique integrates a three-dimensional ray-tracing algorithm with microwave radiometer measurements to jointly correct both dispersive and non-dispersive tropospheric delays. Simultaneously, first- and second-order ionospheric errors are precisely eliminated via dual-downlink inversion of the slant total electron content. To validate this approach, we developed a theoretical analysis and simulation platform that systematically evaluates various factors—including different satellite types, transmission methods (carrier-phase versus pseudocode), and combinations of onboard and ground atomic clocks—to comprehensively verify the correction technique’s effectiveness. Experimental results show that this method can achieve two-way satellite–ground time synchronization accuracy better than 0.3 picoseconds (RMS) when low-earth orbit satellites and ground stations are both equipped with high-stability optical clocks and carrier-phase transfer is used. The Allan deviation of the transfer link’s clock difference is below 5.17 × 10 − 15 at an averaging time of 100 s. These results highlight the significant potential of our approach, offering an innovative solution for all-weather, high-reliability satellite-to-ground time and frequency transfer systems.