This paper describes a transportable system based on synthetic wavelength interferometry for absolute distance measurement. The synthetic wavelength is generated by means of two frequency-doubled Nd:YAG lasers. A superheterodyne technique has been implemented to detect the synthetic phase, enabling a fringe interpolation of ∼2π/5 600. A ∼5 μm accuracy (1σ) is demonstrated over 25 m, based on an indoor comparison with a classical fringe counting interferometer. An outdoor comparison has been carried out on a 864 m-long standard baseline located in Finland (Nummela), yielding an uncertainty of 700 μm (1σ). This work was carried out within the framework of the “Long distance” EMRP project that ended on June 2011.

Key words

laser telemetry
superheterodyne detection