[Shiraz (Ray)]

q1 to dry out the air in the vicinity of the CCD and stop condensation on the cold chip or window

q2 read out noise is a once off noise added to each pixel signal when it is read out from the chip - mainly due to the output amplifier and influenced by readout rate and temperature. Read noise is the most important noise parameter in a CCD spec because it is unavoidable - every time you read out a pixel signal you get read noise. generally given as electrons (RMS)

dark signal is thermally generated charge that has the same characteristics as real signal (eg it builds up as you increase exposure time), but it appears independently of the light falling on the chip - it's even generated when there is no light at all. Depends very much on the CCD technology and it can be reduced by cooling the chip, often to the point where it is insignificant. generally given as electrons/s/pixel for a given temperature.