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Audine with Ethernaude = non-linearity measurements


Radiometric method

I did a few non-linearity measurements on the Audine camera with a radiometric method. My approach was: (1) to illuminate the detector uniformly with a very stable source; (2) to record series of frames at various exposure times ranging from 0.05 sec to 60 sec. So the idea of this non-linearity measurement is that it includes the complete system: detector, pre-amplifier, ADC, and the shutter. As we will see I could clearly detect two different non-linearity sources : a temporal offset understood as coming from the shutter and a more complex non-linear behaviour.

For more details see the following pages:
1- measurement procedure
2- processing and calculation of non-linear response



TDI method

TDI means "time delayed integration". With this read-out method the CCD frame is acquired line by line, with a small delay between each line read-out. The width of the resulting TDI image is the same as for standard images, but the height can be arbitrarily large. The time delay can be calculated, for instance, to match the apparent drift of the sky, so that no right ascension drive is needed on the telescope mount.

TDI can also be used to measure CCD non-linearity : some illumination source is switched on after a TDI acquisition has been started. Then the signal is increasing with time, because the CCD line N+1 is more exposed than CCD line N. If the slope is constant, the signal increase is perfectly linear and so does the CCD detector. Otherwise, there is some non-linearity.

I used this method to try to confirm the Audine non-linearity obtained with the radiometric method. See the results at this page.