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Reducing iso is one way. Cooling is another and more effective. Dark noise doubles with every 6C rise in temperature. Conversly reducing temperature.
Signal to noise ratio can be improved by selecting a suitable iso and exposure time. It could be that the exposure is too short, but, at iso1600 , it's probably not, so temperature is a good guess. Try iso800 and 3 - 3.5 and see what it looks like. Get more signal into the image.
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