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

¹ TMT Observatory Corporation, 2632 E Washington Blvd, Pasadena, CA, 91107, USA
² Herzberg Institute of Astrophysics, 5071 West Saanich Road Victoria, BC V9E 2E7 Canada

^a e-mail: lianqiw@tmt.org

Abstract

For multi-conjugate and multi-object AO (MCAO and MOAO) systems, the evaluation of sky coverage 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. Sufficient computational efficiency 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 affected by the lower-order NGS control loop. We first compute and store time 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 WFS centroiding to maximize skycoverage.