Author: B. Boeckem
Institution: Swiss Federal Institute of Technology, Zurich (ETH)
Co-Author: H. Ingensand
A high-accuracy alignment system based on the dispersion effect
A dispersometer for a metrology solution of atmospheric induced problems in high-accuracy alignment and direction observations is currently under construction at the Institute of Geodesy and Photogrammetry of the Swiss Federal Institute of Technology, Zurich (ETH). This design is capable of true, i.e. refraction compensated angle measurements, the detrimental influence of atmospheric turbulence notwithstanding, by using the two-color method in the dispersive air.
The principle of the two-color method utilizes the wavelength dependence of the refraction index. The difference angle between two light beams of different colors is to first approximation proportional to the refraction angle. Correcting the apparent direction by the refraction angle one will get the refraction free true direction. However the required accuracy can only be achieved by compensating the effects of atmospheric turbulence. In the currently developed dispersometer the same system will be capable of compensating both effects. The new designed dispersometer consists of two submodules, the light source (a dual-wavelength laser by second harmonic generation for blue light and the detector being composed of a dispersion-telescope and a semiconductor-detection system.
It is further planned to integrate each submodul in an existing motorized theodolite.