Logo of the Physikalisch-Technische Bundesanstalt
symbolic picture: "magazines"

A base for long range

Especially interesting for
  • manufacturers of geodetic ranging instruments
  • institutes of geodetic engineering
  • engineering offices
  • land-surveying

Electro-optical distance meter can be calibrated with low uncertainty for applications at ambient conditions on a newly equipped calibration base of PTB. In addition, the baseline, which is equipped with a broad range of environmental sensors, an air-conditioned laboratory and laser-protection measures, allows its users the possibility of verifying and optimizing their geodetic equipment during its development phase.

Verification of an electro-optical distance meter in its development phase, at the 600 m baseline. The posts are equipped with centring devices, the temperature sensors are covered with white protective shafts. The humidity sensors are affixed to the measurement booths. For laser-protection reasons, the fence is cladded with non-transparent foil.

Areas at risk from landslides, potential radioactive waste repositories, but also regions with interesting tectonics are monitored worldwide with the aid of geodetic networks as to position/situation shifts. Hereby, often changes of a few 1/10 millimetres per year are to be detected. But also in classic geodesy, e.g. for cadastral work in expensive locations in the centre of cities, the requirements placed on measurement accuracy are increasing. For this purpose, electro-optical distance meter are used; for their verification and traceability, reference baselines are normally used. Given the required accuracy, various factors influencing the measurand used for optical distance measurements – the propagation velocity of light – have to be checked accurately. Among these factors are, e.g., the ambient pressure, the temperature, and the humidity. In a measurement over 1000 metres, e.g., to attain an accuracy of 1 mm, the mean temperature along the whole section to be tested has to be known with an accuracy of 1 K.

The worldwide unique calibration base developed by PTB makes such accuracies possible for the first time. The 600 m baseline which was set up in the 1970s was equipped with an extensive network of calibrated sensors: 60 temperature sensors, 6 humidity sensors as well as at least 2 pressure sensors allow the effective parameters along the beam path to be determined anew every 30 seconds with low uncertainties. Along the section, the important correction factors of an electronic distance meter can be determined under optimal conditions, in a traceable way, with expanded uncertainties of 61 μm for the offset correction and of 8.2 ∙ 10–7 for the standard correction. In order to be able to use sensitive light sources on site, such as those used in latest-generation electro-optical distance meter, the first post of the calibration base is equipped with an air-conditioned container accommodating a lab. The calibration base is also available to land surveyors, companies and land surveying offices to carry out their own measurements.

Scientific publication

F. Pollinger, T. Meyer, J. Beyer, N.R. Doloca, W. Schellin, W. Niemeier, J. Jokela, P. Häkli, A. Abou-Zeid, K. Meiners-Hagen: The upgraded PTB 600 m baseline: a high-accuracy reference for the calibration and the development of long distance measurement devices. Measurement Science and Technology 23, 094018 (2012)