I've been comparing the spatial noise in the two SRO SASSY maps (0.5 degrees by 0.5 degrees each) to the noise maps produced by the pipeline and matched-filter picard script. I've been told that this is a known issue, but that I should also share my findings. To do this I made histograms of signal to noise pixel values within the two maps that were processed using the matched-filter picard script. Since the maps are mostly empty and the matched-filter script should remove most of the artificial large scale structure introduced by the mapmaker algorithm, the spatial noise should agree well with the noise maps produced by the pipeline.
850μm maps: For the two SASSY fields (one with 29mJy rms and another with 47mJy rms), the signal to noise map underestimates the noise in the map by about 17% (± about 2% since I'm doing this by eye).
Larger image here
450μm maps (we don't expect to see any astronomical signal from these): For the NGC 2559 field with 1700mJy rms, the noise map underestimates the noise in the map by about 29%. For the cirrus field with 2400mJy rms, the noise in the map is overestimated by about 13%.
Larger image here
Larger image here
Hopefully this is helpful for others who are trying to figure out the amount of noise in their maps and are wondering about the accuracy of the noise maps produced by the pipeline.
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