Keywords: class-herschel-fits

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## Intensity array

The intensity array (`RY`) is extracted from one or more columns in the binary table. There are 2 possibilities:

- the `flux_*` columns (where `*` is the subband number), each of them producing a different spectrum (level 2.0). In this case, one row of the column contains all the channel values. The associated frequency array is found in the column `lsbfrequency_*` or `usbfrequency_*`, else an error is raised.
- the `flux` column, producing a single spectrum (level 2.5). In this case one row of the column contains 1 channel value. The associated frequency array is found in the column `frequency` if available, else `wave`, else an error is raised.

All spectra (flux and frequency arrays) are always sorted in ascending frequency (if needed), before setting the spectroscopic section as described in the Table . The Not-a-Number (`NaN`) values (if any) in the flux array are patched to the `bad` value defined in the CLASS header.