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Adding Spectra

Four parameters define the way spectra are added. These are the align mode, the combination mode, the integration weighting, and the behaviour with respect to bad channels.

Four alignment modes are available, by the means of the command SET ALIGN Mode:

CHANNEL, VELOCITY and FREQUENCY are relevant for Line observations, while POSITION is relevant only for Continuum observations. Two combination modes are possible with the command SET ALIGN MODE Combination: Three weighting types may be used, with the command SET WEIGHT Type: Bad channels are dealt with in two possible ways, defined by the command SET BAD Mode: Default values are ALIGN CHANNEL INTERSECT, WEIGHT TIME, and BAD OR.

Two other parameters control whether summing spectra is allowed or not. Positions are checked according to SET MATCH Tolerance or SET NOMATCH. If (absolute) positions differ by more than the tolerance parameter, an error message is generated. The tolerance is specified in current angle units. The homogeneity of the calibration is checked according to the SET CALIBRATION Beam_Tolerance Gain_Tolerance or SET CALIBRATION OFF commands. Beam_Tolerance is the maximum difference allowed in the beam efficiencies to add spectra (default 0.02) and Gain_Tolerance the maximum difference between the gains in the image band (default 0, which means not checked).

There are two ways of adding spectra: the commands AVERAGE and ACCUMULATE. AVERAGE operates globally on all the spectra in the index, while ACCUMULATE adds the R and T buffers into R. AVERAGE is generally better for systematic methods, ACCUMULATE for special cases. The drawback of ACCUMULATE is in the need for initialization; one needs a spectrum in T and a spectrum in R to begin with...


next up previous contents index
Next: Analyzing profiles Up: Spectra Line Processing Previous: Folding Frequency Switched Spectra   Contents   Index
Gildas manager 2018-12-16