PhoSim Featured Project: LSST Photon Simulator

Impact of telescope and atmospheric effects on the LSST PSF, evaluated using PhoSim.

Impact of telescope and atmospheric effects on the LSST PSF, evaluated using PhoSim.

(Author: John Peterson)

The Photon Simulator (PhoSim) is a code to simulate high fidelity astronomical images from optical telescopes. PhoSim uses a novel photon Monte Carlo approach to  simulate the propagation of light through the atmosphere, telescope, and camera. An arbitrary catalog of astronomical sources and their properties is the input to PhoSim.This catalog is then used to sample photons from the astronomical sky. Detailed physics is then used to propagate photons through the atmosphere, follow the photons through arbitrary optical telescope design, and convert the photons in the Silicon of the detectors. A number of detailed physical effects are implemented to simulate each stage in detail.

Alternative telescopes can be implemented in PhoSim, but it was specifically designed for simulations of the Large Synoptic Survey Telescope (LSST). PhoSim can be run on individual computers, but can also be run on large-scale computing for the simulation of large survey. There are a wide range of possible science applications, but it is particularly useful when relatively subtle measurements are being made and systematics are being explored. The PhoSim Team releases PhoSim every 4-6 months to the community and they includes updates based on detailed validation and comparisons with real data.  We expect that the use of PhoSim by the wider community will help to validate PhoSim. The complete description is here. PhoSim can be downloaded at the LSST git repository and is documented on the LSST TRAC pages

PhoSim v3.3 is currently available, and is increasingly used by a larger and larger base of users. Increasingly, PhoSim team members have been concentrating on using PhoSim to simulate a variety of different applications including: prototype LSST devices in laboratories, the primary mirror shapes tests for LSST, the LSST calibration telescopes, and various experiments in simulating other telescopes besides LSST.  We also continue to fix increasingly subtle physics details and increase the usability/documentation in future releases.  In the next release (v3.4) some of the more important changes are allowing for arbitrary surface optical perturbation models to increase the realism of telescope PSF predictions, and calculating accurately the implied lateral fields from impurity variations (i.e. tree rings).