The problem of obtaining formulae for the refractive index of air for high-precision EDM

The causes which prevent an increase in the accuracy of the refractive indices for high-precision electronic distance measurements are described. It is shown that there is a large number of molecular resonances in the visible and IR spectrum which are due to practically all atmospheric components and not just the trace gases. It is also shown that in such conditions the Rayleigh, Lorentz-Lorenz and Sellmeier formulae need to be corrected. Methods for the correction and experimental testing are proposed. Received: 16 July 1996 / Accepted: 27 March 1997