Obsolete
darkCurrentImage = noiseDarkCurrent(ISA)
PURPOSE:
Calculate the current image generated by the dark current. The dark
current image units are Amps.
Programming notes:
For legacy reasons, many of the functions return current. This is one
example routine. It could return voltage (or even electrons) to make
the computations simpler to read. All of the noiseXXX routines could
be changed to conform to this.
This routine should not add in the dark current noise. The noise is
computed as part of the noiseShot calculation, which takes the sum of
the mean signal and the dark signal together. The shot noise is
computed from this total. We don't compute signal noise and and dark
signal noise separately.