"personally doubt that, the ambient temperature will be lower at night there fore the helicopter heat signature would be an even greater target for a heat seeking missile."
Nothing to do with ambient temp.
Heat seaking MPAD user normally scans visually to identify helicopter first, far more difficult to try and search a black sky looking for a blackout helicopter even when you can hear it close by. Unless the MPAD has built in FLIR optics.
We use to practice guiding helicopters in with a special locator tracking beacon at night as part of training for helicopter crews. Blacked out Helicopter at night is hard to pin point even when you know direction its coming from, even something as loud as a UH1.
