The upgraded PTB 600 m baseline: a high-accuracy reference for the calibration and the development of long distance measurement devices

The calibration and verification of high-precision electronic distance meters (EDMs) requires well-characterized and calibrated geodetic baselines. As the length measurements are performed typically over several hundred metres in air, a thorough understanding of the environmental conditions is necessary. In the course of a major refurbishment, the 600 m baseline of the Physikalisch-Technische Bundesanstalt at Braunschweig, Germany, was equipped with a dense environmental sensor network. This paper presents the characterization of this novel reference baseline, including the calibration of the inter-pillar distances, and identifies the major sources of uncertainty for such a length standard. A preliminary expanded standard uncertainty ( k = 2) of is deduced for single-slope distance comparisons on the baseline. In the course of a full calibration, the additive constant c EDM of an EDM can currently be determined with an expanded uncertainty of U ( c EDM ) k = 2 = 6.1 × 10 −5 m, and its scale correction s EDM with an expanded uncertainty of U ( s EDM ) k = 2 = 8.2 × 10 −7 . As an example, a femtosecond laser-based distance measurement over 600 m on this baseline is presented.