Opening a Window of Discovery on the Dynamic Universe

Photon Simulator (PhoSim)

The variation in the LSST PSF as a function of different physical effects. The white line corresponds to the size of one LSST pixel

The Photon Simulator (PhoSim) is a set of fast photon Monte Carlo codes used to calculate the physics of the atmosphere and a telescope and camera in order to simulate realistic astronomical images. It does this using modern numerical techniques applied to comprehensive physical models. PhoSim generates images by collecting photons into pixels. This movie shows the photon Monte Carlo method used in the simulation. 

Physical processes included in the Simulator
  • Photon sampling from galaxy/asteroid/star SEDs & spatial distribution
  • Dust absorption at source and in the Milky Way
  • Von Karman frozen turbulence
  • Atmospheric dispersion
  • Atmospheric molecular opacity and scattering
  • Cloud absorption
  • Reflection/refraction/diffraction of mirrors, lenses, sensors
  • Interference reflection/transmission/absorption of coatings
  • Photo-electric conversion (incl. fringing, field free regions)
  • Charge diffusion (incl. lateral fields, charge sharing)
  • Saturation & blooming
  • Readout:  read noise, dark current, gain, pre-over scans, bias, CTE
  • Hot pixels/columns, dead pixels, lithography errors

Instrument and site characteristics included in the Simulator
  • Site Properties: wind, turbulence intensity, outer scale 
  • Optical design
  • Focal plane layout
  • Obstructions (spider)
  • Tracking of the telescope
  • Surface perturbation & alignment errors of all optics & sensors
  • Mirror, lens, filter, detector coating details
  • Dome seeing
  • Cosmic ray properties
Example of images generated using PhoSim

An example of output catalogs from CatSim and the resulting simulated images are available

  • An example of an input file to PhoSim
  • FITS images generated by these catalogs are here
The full website for PhoSim is available here
  • Phosim installation instructions are available here
  • Tutorials for running and using PhoSim are available here
  • The codebase for the catalog simulations are accessible through Bitbucket

For more details of PhoSim or if you have questions, they can be addressed using

Financial support for Rubin Observatory comes from the National Science Foundation (NSF) through Cooperative Agreement No. 1258333, the Department of Energy (DOE) Office of Science under Contract No. DE-AC02-76SF00515, and private funding raised by the LSST Corporation. The NSF-funded Rubin Observatory Project Office for construction was established as an operating center under management of the Association of Universities for Research in Astronomy (AURA).  The DOE-funded effort to build the Rubin Observatory LSST Camera (LSSTCam) is managed by the SLAC National Accelerator Laboratory (SLAC).
The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.
NSF and DOE will continue to support Rubin Observatory in its Operations phase. They will also provide support for scientific research with LSST data.   

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