Features Implemented in imSim

These summary tables should give a high level overview of effects that have been implemented in imSim. For detailed information please see the linked sub-pages, code, or appropriate reference.

Go directly to: Sensors - Sky - Throughputs - Atmospheric PSF - Optics - Calibration Products

Sensor Effects

This table is a list of sensor effects in imSim along with pointers to the techniques used to implement them, and the internal validation tests that have been performed.

Effect	Implementation	Data / Model Source	Short description	Validation Page and Notebooks
Brighter Fatter	GalSim Feature (Silicon.cpp)	Linear scaling of pixel edge vertices displacement derived with Poisson Solver. Pre-computed solutions available for both E2V and ITL sensors, with both 8 and 32 vertices per edge.	GalSim reads in vertex data from full electrostatic Poisson solver, scales them linearly with collected charges, and co-adds the effects from all pixels iteratively while collecting the image.	Effect: Brighter-Fatter
Diffusion	GalSim Feature (sensor.py / Silicon.cpp)	Diffusion Parameters estimated from first principles and validated with Fe55	GalSim applies random Gaussian displacement for every photon using temperature and voltage dependent amplitude, See page link	Effect: Diffusion
Tree Rings	GalSim Feature (Silicon.cpp) / imSim configuration (tree_rings.py)	Analytic model is used to pre-compute 189 unique sensor models with randomized parameters empirically based on BNL acquired data.	Radial displacement profile is modelled as a sum of 40 sinusoids modulated by a power law function.	Effect: Tree rings
CTE	readout.py	Camera Integration and Testing
Noise Rate	readout.py	Camera Integration and Testing
Xtalk	readout.py	Camera Integration and Testing		Crosstalk values are read from obs_lsst camera discription
Hot Pixels/Rows	being implemented	Camera Integration and Testing
Fringing	being implemented	Sensor Testing and electromagnetic model	Please see: https://inspirehep.net/literature/2183279
Cosmic Rays	cosmic_rays.py: ~10K cosmic are randomly added to the exposures.	Template data taken from ITL test stands at UofA. We should remeasure on summit.
Edge rolloff	Not yet
Bleeding	bleed_trails.py called from readout.py	Test stand at Davis. Specialized bleed runs.

Sky Model

imSim uses the Rubin project sky model. It is called sims_skybrightness and is located in the rubin-sims package which is an imSim dependency.

Effect	Implementation	Data / Model Source	Short description	Validation Page and Notebooks
Sky Background	See here	Based on the ESO sky brightness model and all-sky camera data from LSST site for twilight sky.	The model includes light from twilight (scattered sunlight), zodiacal light (scattered sunlight from SS dust), scattered moonlight, airglow, and emission lines from the upper and lower atmosphere. The model can return SEDs or magnitude per sq arcsec in LSST filters.	Validation plots can be found in the SPIE paper. Note the model does not include any “weather” (e.g., clouds, variable OH emission). There is an option to change the solar activity, which scales the airglow component.

System Throughputs

All of the system throughputs are recorded in the throughputs baseline. This information is copied from the System Engineering database. More information can be found in the README file. In that directory you can find a graphical representation of the total throughput along with datafile representing each component and the total throughput. The file representing each throughput curve is referenced below.

Effect	Implementation	Data / Model Source	Short description	Validation Page and Notebooks
Camera QE and AR	detector.dat	SysEngineering 1.7	Expected response (QE response + AR coatings) of the CCDs. Currently, these numbers are joint minimums of the responses of the two vendor’s sensors (e2V and ITL).
Lens	lens[1,2,3].dat	SysEngineering 1.7	Combination of fused silicon and BroadBand AntiReflective (BBAR) coatings
Filters	filter[u,g,r,i,z,y].dat	SysEngineering 1.7	Filter throughput in each band. We expect an update with as-built numbers soon.
Mirrors	m[1,2,3].dat	SysEngineering 1.7	Reflectivity curve for each mirror
Atmosphere	atmosphere_std.dat and atmosphere_10.dat	SysEngineering 1.7	MODTRAN based standard US atmosphere with Aerosols added.	Both typical (standard) throughput with airmass X=1.2 and optimum X=1.0 files are provided
Total	total[u,g,r,i,z,y].dat	SysEngineering 1.7	The total throughput by band

Note

The hardware[u,g,r,i,z,y].dat files contain everything except atmospheric effects. Multiplying those with the atmosphere results in a total throughput curve. Atmospheric throughputs for a large set of atmospheres can be found in https://github.com/lsst/throughputs/tree/main/atmos.

Atmospheric PSF model

Note

To be added. See the atmospheric psf config section on how to configure the atmosphere and in https://iopscience.iop.org/article/10.3847/1538-4365/abd62c for a description of the model.

Optical model

You have a choice of parametric of fully raytraced optics via batoid.

Effect	Implementation	Data / Model Source	Short description	Validation Page and Notebooks
Vignetting	vignetting.py		Either emergent for raytraced objects or via a function for those produced via FFT. The sky backround is vignetted via a function.
Ghosts	Not currently possible. Planned in the next version of imSim when the abilty to handle raytraced light across multiple sensors being processed in parallel will be updated.
Spider Diffraction Spikes	diffraction.py, diffraction_fft.py photon_ops.py		Statistical Diffraction during batoid ray tracing or parametric model with FFT.	Page link Effect: Diffraction
Aberrated optics	optical_system.py telescope_loader.py		Either a parametric model built around a sensitivity matrix, or a fully raytraced optical model with FEA and pertubation controls using several degrees of freedom including bending modes and physical actuators.	Page link Effect: Abberated Optics for the parametric case The Rubin Optical System for the raytraced case.

Calibration Products

Note

To be added. Description of flats, darks etc need to be added.

Detailed Description of Physical Effects Implemented in imSim

Several of the effects listed above have detailed pages descrubing how the model was constructed and what data was used.

• Effect: Abberated Optics
  • Contact person(s) if any:
  • Reference Material:
  • Data Provenance:
  • Model Details:
  • Validation Criteria:
  • Validation Results:
  • Known Issues
• Effect: Brighter-Fatter
  • Contact person(s) if any:
  • Reference Material:
  • Data Provenance:
  • Model Details:
  • Validation Criteria:
  • Validation Results:
  • Relevant Project Team for input if any:
  • Release and approval log:
• Effect: Diffraction
  • Contact person(s) if any:
  • Reference Material:
  • Data Provenance:
  • Model Details:
  • Validation Criteria:
  • Validation Results:
  • Relevant Project Team for input if any:
  • Release and approval log:
• Effect: Diffusion
  • Contact person(s) if any:
  • Reference Material:
  • Data Provenance:
  • Model Details:
  • Validation Criteria:
  • Validation Results:
  • Relevant Project Team for input if any:
  • Release and approval log:
• Effect: Tree rings
  • Contact person(s) if any:
  • Reference Material:
  • Data Provenance:
  • Model Details:
  • Validation Criteria:
  • Validation Results:
  • Relevant Project Team for input if any:
  • Release and approval log: