signal-to-noise ratios

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This form allows you to calculate the signal-to-noise ratio of an ULTRACAM exposure. The default parameters are for a 1-second, dark-time, exposure of a V=20 magnitude object at the zenith, as observed in 0.7 arcsecond seeing at the GHRIL focus of the 4.2-m WHT on La Palma using ULTRACAM with a Marconi CCD47-20 chip and an SDSU controller. Certain parameters are hard-wired into the signal-to-noise calculation. These are: The sky brightness in magnitudes/arcsecond2 in each filter bandpass for dark, grey and bright phases of the Moon, as measured on La Palma. The number of photons/second/Angstrom/cm2 received from a star of zero magnitude in each filter bandpass above the Earth's atmosphere. The extinction per airmass in magnitudes, as measured on La Palma. The quantum efficiency of the Marconi CCD47-20 chip in each filter bandpass. The bandwidth of each filter in Angstroms. The signal-to-noise is calculated by assuming that the object counts are extracted using a circular aperture with a radius equal to the seeing. The noise due to atmospheric scintillation is also calculated, using equation 10 of Dravins et al. (1998, PASP, 110, 610). Note that the noise quoted only strictly applies to integration times longer than it takes a turbulent cell to cross the telescope aperture, i.e. longer than approximately 1 second for 2-4 m class telescopes. Higher frequency scintillation, due to the boiling of individual speckles, obeys a much steeper aperture dependence than that assumed here and so is much less important.
object magnitude
exposure time	seconds
filter (U/B/V/R/I/Z)
moon (D/G/B)
airmass
collecting area	cm2
telescope throughput
ULTRACAM throughput
empirical/theoretical throughput ratio
seeing	arcseconds
platescale	arcseconds/pixel
dark current	e-/pixel/hour
readout noise	e-/pixel

 

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