Astronomy & space · Advanced university
Poisson photon-count signal-to-noise · formula reference
Assume independent source and background Poisson noise and a background expectation known without extra uncertainty.
Formula
Assume independent source and background Poisson noise and a background expectation known without extra uncertainty.
SNR ≈ S/sqrt(S+B)
Worked example
A photon-count model expects S=1000 source counts and B=220 background counts. Use SNR=S/sqrt(S+B), neglecting other noise. Find SNR. Round the final result to 4 decimal places if needed.
Poisson variances add: total variance is 1220; divide source signal by its square root.
28.6299
Prerequisites and checking
Algebra and the topic definitions. Keep units and rounding consistent. State the model conditions before applying the formula.
Further reading and review references
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