SNR maps

[SoFiA-Admin]

Some users have expressed the wish for SoFiA to provide maps of statistical uncertainty or signal-to-noise ratio associated with moment maps produced by SoFiA. A similar feature would also be useful for integrated spectra. Note that SoFiA already produces a ‘number of channels’ map whenever moment maps are requested. This could in principle be used to recover the statistical uncertainty in each pixel of the moment-0 map.

The question is whether we actually want to provide uncertainty or SNR maps instead of leaving this job to the user? The risk is that we would have to make several assumptions for this to work, e.g. the assumption that neighbouring spectral channels are uncorrelated. Similarly, for uncertainty spectra we would need to make assumptions about the beam size and hence the correlation of spatial pixels. The purpose of this issue is to provide a forum for discussion of this topic.

[SoFiA-Admin]

As a first step towards this goal I have modified the code that generates integrated spectra to include another column that lists the number of spatial pixels contributing to the signal in each channel of the spectrum (see b97883a1be48cd9019ee73c0f691e798678dc5a4). That information was previously missing and should in principle enable user to calculate the SNR across the spectrum.