Introducing atmospheric effects in the numerical simulation of the VLT/MUSE instrument

The Multi Unit Spectroscopic Explorer (MUSE) instrument is a second-generation integral-field spectrograph in development for the Very Large Telescope (VLT), operating in the visible and near IR wavelength range (465-930 nm). Given the complexity of MUSE we have developed a numerical model of the instrument, which includes the whole chain of acquisition from the atmosphere down to the telescope and including the detectors, and taking into account both optical aberrations and diffraction effects. Simulating atmospheric effects such as turbulence, refraction and sky background within an instrument numerical simulator is computation intensive, and the simulation of these effects is usually beyond the scope of an instrument simulator as it is done in dedicated simulations from which only the results are available. In this paper we describe how these effects are simulated in the VLT/MUSE numerical simulator, the simplifications that are used, as well as the assumptions leading to these simplifications.