On traceability of long distances

Abstract

Geodetic baselines are used to determine traceable lengths in geospatial applications. The 864-m-long Nummela Standard Baseline in Finland is a world-class length standard, which is used in calibrations of the most precise electronic distance measurement (EDM) instruments and in scale transfers around the world. At the moment new instruments based on new technology are developed to measure long distances; this is also a joint research project of the new European Metrology Research Programme (EMRP). As the state-of-the-art, the Nummela Standard Baseline is available for testing the new instruments in field conditions. The baseline was remeasured with the Väisälä interference comparator to 432 m in autumn 2005, and to 864 m in autumn 2007 with better than 0,1 mm standard uncertainty. We present here the results, which again verify the long-term stability of the baseline and excellent repeatability of measurements. We also present an example of a recent scale transfer to a calibration baseline and test field in Lithuania. In addition to national calibration activities, this Kyviškės Calibration Baseline serves in our new research project concerning the scale of precise GPS positioning. Brief introductions to another new geodetic baselines in Austria and Estonia are also given.