Fig. 1. Schematic of four-satellite-to-earth unidirectional time transfer by Beidou laser link

Fig. 2. Calculation method of timing deviation caused by atmospheric refraction under Beidou unidirectional time transfer by laser link

Fig. 3. Atmospheric refractive index layered model. (a) Laser transmission path; (b) refractive index variation profile

Fig. 4. Timing deviation caused by atmospheric refraction at 00:00 of every day in August 2023 under the cumulative monthly mean atmospheric refractive index stratification model at each station

Fig. 5. Timing deviation caused by atmospheric refraction at 00:00 of every day in August 2023 under the atmospheric refractive index stratification model with measured daily values at each station

Fig. 6. Difference in timing deviation calculated by the two models at 00:00 of every day in August 2023 at each ground station