Like any other ground-based millimeter continuum observations, our default data processing attempts to remove the Earth’s atmosphere with either a common-mode subtraction or something quite similar to it (e.g. PCA).
An early memo on filtering compared the results using two different (Lissajous daisy) scan sizes and two different sets of filtering parameters, with an executive summary here and a more in-depth tabulation here.
The above plots show transmission functions for a broad range of (Lissajous) scan sizes (from 2.5′ to 5.0′) with a fairly gentle filtering (3 components subtracted from the timestreams via PCA and a windowed filter, keeping frequencies between 0.06 Hz and 41.0 Hz). Below are the same scan sizes filtered with 5 components (via PCA) and a window between 0.08 Hz and 41.0 Hz.
Splitting the scan sizes among two plots below that show the differences between these two reductions:
A filtering with a highpass of 0.06 Hz is, unfortunately, a bit more gentler than we find is necessary. Rather, a highpass at 0.07 or 0.08 Hz often results in acceptable noise in our maps. There are still other datasets which require still more aggressive filtering, either a highpass at 0.09 Hz, or even 0.1 Hz.
A repository of transfer functions (ascii files) is available here.