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Homework Help: Signal to Noise ratio in CCD

  1. Apr 26, 2012 #1
    1. The problem statement, all variables and given/known data
    The 2-D image of a faint galaxy observed by a CCD covers 50 pixels. For an
    exposure of 5 seconds a total of 10^4 photo-electrons are recorded by the CCD
    from these pixels. An adjacent section of the CCD, covering 2500 pixels, records
    the background sky count. During the same exposure time a total of 10^5 photoelectrons
    are recorded from the adjacent section. Show that, after subtracting
    the background sky count, the signal-to-noise ratio for the detection of the
    galaxy is estimated to be 73.

    2. Relevant equations
    Average count rate = [itex]\hat{R}[/itex]=Nobs/t

    3. The attempt at a solution

    Number of photons per pixel per second due to galaxy + background + noise = 40
    Number of photons per pixel per second due to background + noise = 8
    So there 32 "signal" photons per second per pixel.

    I am unsure how to calculate the average noise per pixel.
    Any help is appreciated.
  2. jcsd
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