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Knowledgebase: IRAC
What is the first-frame effect and why should I worry about it?
Posted by Elena Scire on 25 February 2020 08:07 AM

There is an electronic history effect in the IRAC arrays that produces an offset pattern in each Fowler frame image. The strength and shape of the patterns depend on the history of how an array was clocked during the time -- from seconds to days -- preceding the beginning of an integration. The time an array spends idling just before an image, the FRAME DELAY, has the greatest effect. We call this the "first-frame effect" as it was seen to be largest in the first frame of long sequences in lab tests.

Cryogenic mission:

The channel 3 array had the largest effect in the cryogenic mission (see Section.1.10). The first frame correction is applied in the IRAC pipeline for all cryo mission data. Unfortunately, all of the effect was not removed because the instrument was operated differently in-flight than in lab tests for other reasons.

Post-cryogenic Warm mission:

The effect in channel 1 was larger than channel 2. There were no corrections for this effect in the warm mission pipeline because the instrument operated at a higher temperature than the cryogenic mission.


The effect of poorly corrected or uncorrected first-frame effect on aperture photometry is probably small, except perhaps for the first few BCDs of an AOR ( in cryo channel 3 or post-cryo channel 1).  One should be careful in interpreting background gradients in these data as well.

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