Comparison between a Two-Wavelength Absolute Distance Meter and a GNSS-Based Distance Meter at CERN Geodetic Network

[EN] Absolute distance determination, which is the determination of distances consistent with the International System of Units (SI) definition of meter, is a current challenge for distances of several kilometers in the open air and with submillimetric accuracies, which is being increasingly demanded for scientific and technological applications. We present the first comparison of two techniques recently developed for this purpose: the Arpent Absolute Distance Meter and the improved Global Navigation Satellite System (GNSS)-based distance meter. Both techniques have been tested and compared on the European Organization for Nuclear Research (CERN) geodetic network during a 2-week observation campaign. The results obtained include the rigorous determination of the uncertainties for both methodologies. In the end, four baselines of 2.2, 4.8, 6.0, and 6.5 km were measured, and for three of them, the differences between the two systems were less than 0.7 mm. The baseline of 4.8 km showed a difference of 2.7 mm, i.e., about 0.6 parts per million (ppm): in the case of conventional optical telemetry, such an agreement would require refractivity correction with knowledge of the air temperature and pressure at better than 0.6 K and 0.15 hPa, respectively.