DYNAMIC AIR TURBULENCE COMPENSATION FOR AN INTERFEROMETRIC MEASUREMENT APPARATUS

摘要

An interferometric measurement apparatus for providing a distance measurement to a movable object. Air turbulence due to fluctuations in the temperature induces noise into the interferometric measurement, as the reflactive index of air is altered. A compensation value is generated for compensating the temperature induced noise. For this purpose, the measurement apparatus includes an acoustic system which transmits a pulse of sound between the moveable object and a reference object and outputs upon receipt of the transmitted pulse a time of flight values. A path length associated with each of the time of flight values is estimated on the basis of a plurality of interpolated interferometric distance measurements. A compensation system generates a compensation value derived from at least one time of flight value and its associated plurality of interferometric distance measurements.