查看“信噪比”的源代码

The signal-to-noise ratio of an observation is:
 s/n = Ct/[sqrt(sigma^2*n+t*(C-A*S))]
where C is the count rate from the object (photons per second), t the exposure time, sigma the read-out noise of each pixel, n the number of pixels on which the image falls, S the number of photons from the sky per unit solid angle, and A the solid angle subtended by the image.

Through-put Measurements and SNR[http://www.noao.edu/kpno/manuals/l2mspect/node12.html]