You've probably seen several maps that show the faint linear striations visible in the following 850 map.
Well, in at least some cases, these striations seem to be due to bad bolometers that have a very different common-mode signal to the others. The map-maker has an algorithm that looks for and rejects such bolometers, but by default the rejection criteria are fairly weak, so few samples are rejected. Changing the com.corr_abstol value from its default of 0.2 to 0.8 produces the following map:
The striations are much less noticeable (both these images use the same grey scale). The down-side to this is that since more bolometer samples are rejected, there are fewer samples to form the map. For the first map, only 1.6 % of the available samples were rejected due to common-mode mis-match, leaving a total of 65.4 % available for the map. For the second map, 11.1 % were rejected due to common-mode mis-match, leaving 55.9 % available for the map.
Going even further, the following map was created with com.corr_abstol set to 0.97 and com.gain_fgood set to 0.5:
Here, 38.5% of samples were rejected due to common-mode mismatch, leaving only 28.6 % available for the map. You can see that the striations have been almost completely removed, but at the expense of higher noise.
Well, in at least some cases, these striations seem to be due to bad bolometers that have a very different common-mode signal to the others. The map-maker has an algorithm that looks for and rejects such bolometers, but by default the rejection criteria are fairly weak, so few samples are rejected. Changing the com.corr_abstol value from its default of 0.2 to 0.8 produces the following map:
The striations are much less noticeable (both these images use the same grey scale). The down-side to this is that since more bolometer samples are rejected, there are fewer samples to form the map. For the first map, only 1.6 % of the available samples were rejected due to common-mode mis-match, leaving a total of 65.4 % available for the map. For the second map, 11.1 % were rejected due to common-mode mis-match, leaving 55.9 % available for the map.
Going even further, the following map was created with com.corr_abstol set to 0.97 and com.gain_fgood set to 0.5:
Here, 38.5% of samples were rejected due to common-mode mismatch, leaving only 28.6 % available for the map. You can see that the striations have been almost completely removed, but at the expense of higher noise.
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