  Characterizing the PSF of adaptive optics instruments is of paramount
importance both for instrument design and observation planning/optimization.
Simulation software, such as PASSATA, have been successfully utilized for PSF
characterization in instrument design, which make use of standardized
atmospheric turbulence profiles to produce PSFs that represent the typical
instrument performance. In this contribution we study the feasibility of using
such tool for nowcast application (present-time forecast), such as the
characterization of an on-sky measured PSF in real observations. Specifically
we will analyze the performance of the simulation software in characterizing
the real-time PSF of two different state-of-the-art SCAO adaptive optics
instruments: SOUL at the LBT, and SAXO at the VLT. The study will make use of
on-sky measurements of the atmospheric turbulence and compare the results of
the simulations to the measured PSF figures of merit (namely the FHWM and the
Strehl Ratio) retrieved from the instrument telemetry in real observations. Our
main goal in this phase is to quantify the level of uncertainly of the AO
simulations in reproducing real on-sky observed PSFs with an end-to-end code
(PASSATA). In a successive phase we intend to use a faster analytical code
(TIPTOP). This work is part of a wider study which aims to use simulation tools
joint to atmospheric turbulence forecasts performed nightly to forecast in
advance the PSF and support science operations of ground-based telescopes
facilities. The 'PSF forecast' option might therefore be added to ALTA Center
or the operational forecast system that will be implemented soon at ESO.
