Research on Atmospheric Correction Technology for Subpicosecond Satellite Earth Time Frequency Comparison Microwave Link

Objectives: The development of high-precision atomic clocks in space is an important research direction for cutting-edge scientific exploration and time-frequency system establishment both domestically and internationally. Among them, how to establish a high-precision satellite ground time difference measurement in comparison link, objectively and accurately evaluate the effectiveness of the space clock group, and promote the application of high-precision time-frequency benchmarks is an urgent core capability that needs to be formed to establish a space time-frequency system. In the entire satellite ground time-frequency comparison link, atmospheric transmission error is the largest source, so the correction of atmospheric transmission error is the key to satellite ground time-frequency comparison. Methods: We focus on the long-term high stability requirements of the satellite ground microwave time-frequency link of the Chinese space station, analyze the impact of the ionosphere and troposphere in the space transmission environment, propose a "three frequency link" combination cancellation method, and construct error correction models for the ionosphere and troposphere respectively. We use uplink and downlink to eliminate the non-dispersion effect in the troposphere, and use two downlink links to calculate the total ionospheric electron content of the same path, thereby correcting the delay error caused by the ionosphere. At the same time, we used a combination of model correction and microwave radiometer measurements to correct the tropospheric dispersion error in the high-frequency signals. Results: The results indicate that the error correction model can achieve satellite to ground microwave time transfer with measurement accuracy below 1 picosecond. Conclusions: The accuracy meets the time frequency transmission stability index of the Chinese space station, which can further support the long-term stability requirements of the E-18 level cold atomic clock.