Background Approximations
Background is the largest source of photons in astronomical images. Therefore there are three levels of approximation that allows a tradeoff between fidelity and speed. The three approaches are listed below.
Embedded Files
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Background Approximation Type PhoSim Commands Wall time/Chip Description of Approximation
Single Photon (No approximation) singlephotonbackground 2 hours * f No approximations: Backgrounds are generated one photon at a time
[Not necessary except for or with full physics identical to normal sources
validation purposes] backalpha0.0
backgamma 1.0
Normal Background normalbackground 6 min * f Standard approximation that is almost perfect. It sends photons in
[Recommended for detailed or groups prior to interacting with sensor; This gets all sensor physics correct
science studies] backalpha 0.2 (which particularly modifies background patterns) & all throughput
backgamma 1.0 (including vignetting) correct; Does not affect any normal sources
[Also this is the default,
no commands necessary]
Quick Background quickbackground 2 min * f Same as above but also averages over physics on small spatial scales in
[Recommended for any quick or sensor; Would only modify the autocorrelations of the background & blur
analysis] backalpha 0.5 debris/contamination on detector; Gradients are accurate to less than 0.2%
backgamma 50.0 and large-scale artifact fluctuations are not visible with smoothing; Does
not affect any normal source photons
f = (16/N_thread ) * [(Area_chip/f#/f#)/(1 sq. cm)] * (t_exposure / 1 min)
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