Full Physical Optics Sky Coverage Simulation for MCAO Systems on ELT's

For multi-conjugate and multi-object AO (MCAO and MOAO) systems, the evaluation of sky cov- erage is challenging because asterisms of three or more natural guide stars (NGS's) must be considered. In this paper, we described a full rank, physical optics sky coverage simulation tool for modeling both the NGS and LGS AO control loops of MCAO systems on ELT's. Su cient computational e ciency to enable practical Monte Carlo simulations over a large number of natural guide star asterisms can be obtained using the so-called "split tomography" control architecture, in which the higher-order wavefront correction computed from the LGS WFS measurements is not a ected by the lower-order NGS control loop. We first compute and store tim e histories of 1) the atmospheric modes that are blind to LGS WFS and 2) natural guide star point spread functions for a full ensemble of many NGS over the course of a single high order AO simulation run. The behavior of the NGS loop may then be evaluated separately for each NGS asterism in a post-processing step to derive sky coverage statistics. This post-processing analysis also helps us find the best approach to WF S centroiding to maximize skycoverage.