Atmospheric refraction corrections in ground-to-satellite optical time transfer.

Area of Science:

• Physics
• Metrology
• Geophysics

Background:

• Free-space optical techniques achieve femtosecond synchronization for ground stations over tens of kilometers.
• Intercontinental optical time transfer is essential for advancing optical frequency standards and redefining the SI second.
• Fiber optic limitations necessitate satellite-based free-space methods for long-distance time transfer.

Purpose of the Study:

• Investigate the impact of atmospheric refraction on ground-to-space optical time transfer.
• Quantify the systematic error introduced by excess optical path length due to atmospheric refraction.
• Develop necessary corrections for accurate time transfer involving space-borne objects.

Main Methods:

• Analysis of systematic effects in free-space optical time transfer.
• Modeling the influence of atmospheric refraction on optical path length for satellite links.
• Evaluating the dependence of refraction errors on elevation angle, temperature, pressure, and humidity.

Main Results:

• Atmospheric refraction introduces a significant systematic error in optical time transfer, previously unstudied.
• This error can reach picosecond levels at low satellite elevations and remains considerable up to ~35 degrees.
• Orbital motion complicates the cancellation of refraction effects, even with two-way techniques.

Conclusions:

• Atmospheric refraction is a critical systematic effect that must be accounted for in ground-to-space optical time transfer.
• A temperature-, pressure-, and humidity-dependent correction is required to mitigate refraction-induced timing biases.
• This correction is vital for achieving high-accuracy time transfer and supporting future metrological advancements.