Metrology for long distance surveying – a joint attempt to improve traceabili - ty of long distance measurements

A number of applications, e.g., the estab ~ ishment of local ties at geodetic fundamental stations, but also the maintenance of surveillance networks require distance measurements over hundred metres or more with uncertainties at the millimetre level or even below. However, based on the current state of technology and understanding of perturbing influences, a measurement traceable to the Sl definition of the metere with such uncertainties is extremely challenging or even impossible. The accuracy of electrooptic distance metres (EDMs) on one hand is primarily limited by the imperfect knowledge of the index of refraction of air, the measurement uncertainty of distance measurements based on Global Navigation Satellite Systems (GNSS) is even more difficult to quantify. In a joint research projects of 12 European institutions, scientists from national metrology institutes have united with partners from geodesy to develop novel technological and methodical solutions to understand, to quantify better, and to reduce the uncertainty of this kind of measurements, in particular fostering traceability to the Sl unit metre. In case of optical distance metrology, refractivity-compensated primary and transfer standards will be developed and applied to reference baselines in Europe. Furthermore, completely novel approaches based on femtosecond laser sources will be explored and set up. In case of GNSS-based distance metrology, a systematic investigation of sources of uncertainty will performed, leading to a sound uncertainty budget. Two different near real-time 3D monitoring systems will be developed and compared at geodetic fundamental stations. The contribution wants to present the concept and the scientific and technological ideas of the project which starts on July 1st 2013, inviting the geodetic community to provide guidance and feedback.