The difference between the first raw bias and the second raw bias (in
ADU) shifted by 10x10 pixels, is computed (per port). This is the
combination of fixed pattern noise and read out noise (scaled by
sqrt(2)). The population standard deviation of this difference is
computed and divided by the square root of 2. The read out noise
contribution evaluated as QC OUTi RON is then quadratically subtracted
from the total noise.