High fidelity sky coverage analysis via time domain adaptive optics simulations.

We describe a high fidelity simulation method for estimating the sky coverage of multiconjugate adaptive optics systems; this method is based upon the split tomography control architecture, and employs an AO simulation postprocessing technique to evaluate system performance with hundreds of randomly generated natural guide star (NGS) asterisms. A novel technique to model the impact of quadratic wavefront aberrations upon the NGS point spread functions is described; this is used to model the variations in system performance with different asterisms, and is crucial for obtaining accurate results with the postprocessing technique. Several design and algorithm improvements help to reduce the residual wavefront error in the tip/tilt and plate scale modes that are controlled using the NGS asterism. These improvements include choosing the right wavefront sensor (WFS) pixel size, optimal pixel weights, and type II control of the plate scale modes.