2.5. Spectrum specialised datasets

2.5.1. Spectrum1d

Spectrum1d contains a one-dimensional representation of a spectrum. It consists of a Table Dataset with the following columns:

  • A flux column (double 1D)

  • A wavelength/frequency column (double 1D)

  • A weight column (double 1D)

  • A segments column (double 1D). The values within this array indicate to which segment the corresponding flux/weight/flag/wave belong. The spectrum can be made of several segments or smallest spectrum component dealt with by the DP system. For example, a spectral segment can be an extracted piece of a spectrum to be used for fitting purposes.

  • A flag column (integer 1D).

A Spectrum1d can also have metadata (header information) added. In general the meaning of the flags is stored in the metadata.

2.5.2. Spectrum2d

For multiple spectra taken in an observation, a 2D structure is required. The components of a Spectrum2d dataset are similar to that of a Spectrum1d dataset, except for having a second dimension. An additional component is the ability to contain subbands. Subbands are vertical splits in the Spectrum2d columns equivalent to the segment column in Spectrum1d. A clear example of its usefulness is the storage of the output from the HIFI spectrometers where several CCD or autocorrelator readouts lead to several "chunks" (subbands) of spectra in one data frame.

Spectrum2d consists of a Table Dataset with the following columns:

  • A flux column (double 2D), where the first axis runs over the spectral dimension and the second axis runs over e.g. time.

  • A wavelength/frequency column (double 2D)

  • A weight column (double 2D)

  • A flag column (integer 1D). In general the meaning of the flags is stored in the metadata.

  • (Optional) a subband start column (integer 1D), which indicates where in the arrays a subband starts.

  • (Optional) a subband length column (integer 1d). Indicates the length of the array section that a subband covers.

A Spectrum2d can also have metadata (header information) added.