Simulation of the effects of atmospheric turbulence on mid-infrared visibility measurements with the mid-infrared interferometric instrument for the Very Large Telescope Interferometer

Abstract

The mid-infrared interferometric instrument is one of three instruments that will equip the focus of the Very Large Telescope Interferometer. During the design phase of the instrument we made use of a program of simulations to define the constraints imposed by atmospheric turbulence. We present our results for the estimated fringe motion, during a typical sampling time of 100 ms, and for the estimated fringe visibility with and without tip-tilt correction. Our simulations were run assuming an outer scale of turbulence of 25 m against an infinite value as strictly implied by Kolmogorov statistics. The results show that this has positive consequences for our applications, above all as far as fringe motion is concerned. We also take into consideration the effect of background noise on the accuracy of the fringe visibility measurements and the effect of self-fringe tracking, which has been simulated by a linear fringe-tracker algorithm.