WP1: Optical distance measurements in air

Refractivity‑compensated distance meters are being developed in the course of the project, capable of measuring distances up to 1 kilometre in air with a relative uncertainty of 10-7. They will be compared and validated to the best state‑of‑the‑art distance meters, including the Väisälä method at Nummela. After this comparison, the devices will be immediately able to serve as primary and transfer standards for baseline calibrations of optical distance meters for daily work in surveying, significantly strengthening the traceability chain in this discipline. In parallel, novel metrological sensors for optical inline thermometry and turbulence measurements are being developed to improve the understanding of respective effects on the achievable measurement uncertainty.

Schematic of the measurement head of a refractivity-compensated EDM ((c) by PTB)

Outdoor verification measurement of the distance meter developed by CNAM at the Forêt de Montmorency ((c) by CNAM)

  1. The prospective novel primary standard (TeleYAG) and the prospective high performance transfer instrument (TeleDiode) for long distances developed in WP1 have already achieved remarkable resolutions: a standard deviation better than 1 over 12000 was observed for TeleYAG for a synthetic wavelength of 7.5 mm and better than 1 over 100000 for Telediode for 30 cm of synthetic wavelength (both on short, but macroscopic distances in air).
  2. Both projects in WP1 have constructed outdoor‑capable measurement heads, an important prerequisite to achieve the goal to become a novel primary or low-uncertainty transfer standard for baseline calibrations.
  3. Recently, the performance of the Telediode EDM outdoor has already been preliminary investigated at the Forêt de Montmorency near Paris. For a distance measurement of about 970 m at 1550 nm wavelength a standard deviation of 12 µm could be obtained, giving reason for optimism for the performance of the complete system.
  4. INRIM has implemented its ideas for an optical device to study the influence of turbulence on optical distance measurements. Thus, in the second half of the project, WP1 will be able to deliver novel data for this inevitable problem, leading to a better understanding of the corresponding quantitative impact on the uncertainty.

Further information on the progress of this Workpackage can be found, e.g., Opens internal link in current windowhere and Opens internal link in current windowhere.