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Question about Mosaics when panels have varying SNRs

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Molecular Cloud
Joined: 7 months ago
Posts: 1
Topic starter  

When one panel is say 20 hours of data and another adjoining one is 1 hour of data and the object of interest is in both panels, how does APP handle it? Will the higher SNR data be favoured in the final mosaic or is the high and low SNR data averaged? The 1 hour panel is to give some 'breathing space' around the target for compositional options.

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Universe Admin
Joined: 6 years ago
Posts: 5701

The higher SNR panel will likely be chosen as the reference I think. The result will be what you would expect, more noise in the panels with less data.

Neutron Star
Joined: 6 years ago
Posts: 157


An interesting question and I'm not sure I have the mathematical nous to give a full answer.  

However as I understand your question, you have two overlapping mosaic panels, A and B.   For the area of the final image covered only by the area of Panel A there can be no improvement in SNR (or noise reduction) as there is no data from which to accumulate additional signal. Equally, for the area of the final image covered only by the area of Panel B, there can be no improvement in SNR (or noise reduction) as again there is no source of additional signal.   Lastly, in the area that is covered by both Panel A and Panel B I think it reasonable to expect that there might be a small SNR improvement /noise reduction as there is additional data available.

The interesting question then (for which I am not certain of the answer) is whether APP would actually show an improved SNR measurement in the final combined image bearing in mind that the SNR given by APP would be for the combined image area not for the specific areas sourced from Panel A, Panel B, and Panels A and B.  For me the answer probably depends on the degree of overlap between the two panels.  If the area of overlap is large the total area of the final image will be dominated by the area for which we might anticipate a small noise reduction.

There is also a question (and possibly actually the more important) of whether in post-processing the area of the combined image that is most noisy can be presented in such a way that it does not visually detract from the areas of the image where the noise is least!

I wish I could give a more definitive answer but there's my reasoning for what its worth.



This post was modified 7 months ago 4 times by mestutters