113 km absolute ranging with nanometer precision

Accurate long-distance ranging is crucial for diverse applications, including satellite formation flying, very-long-baseline interferometry, gravitational-wave observatory, geographical research, etc. The integration of the time-of-flight measurement with phase interference in the dual-comb method enables high-precision ranging with a rapid update rate and an extended ambiguity range. Pioneering experiments have achieved remarkable absolute ranging precision over short paths. However, achieving similar precision over longer distances remains technically challenging due to high transmission loss and noise. In this article, we propose a bistatic dual-comb ranging (BDCR) approach that enables successful ranging over a distance of 113 kilometers. We employ air dispersion analysis and synthetic repetition rate technique to extend the ambiguity range of the inherently noisy channel beyond 100 km. The achieved ranging precision is 11.5 μm @ 1.3 ms, 681 nm @ 1 s, and 82 nm @ 21 s, as confirmed through a comparative analysis of two independent systems. The advanced long-distance ranging technology is expected to have immediate implications for space research initiatives, such as the space telescope array and the satellite gravimetry.