3.1.32. Vbin: variable rebinning of the data¶
This command rebins (a part of) the data (thus both the spectrum and the response) such that the signal to noise ratio in that part of the spectrum is at least a given constant. Thus instead of taking a fixed number of data channels for binning, the number of data channels binned is here variable as is the bin width. On top of specifying the S/N ratio, you also specify the minimal bin width. This is useful for rebinning low count data, which have no strong or sharp features or lines in it.
For high resolution spectra with sharp and strong lines, this binning can lead to very wrong results. In this case either the emission lines or the continuum (in case of absorption lines) have a much higher signal to noise ratio than the other component. As a result this function will try to bin the line and continuum together, resulting in a smoothing out of the lines.
It is not always guaranteed that the minimum signal-to-noise ratio is obtained in all channels. This is an effect of the applied algorithm. Channels with the highest S/N ratio and neighboring bins are merged until sufficient S/N ratio is obtained. This process is continued for the remaining number of bins. At the end of the process a few bins with a low S/N ratio will remain. These are merged with their neighbors, resulting in a possibly lower S/N ratio for that bin.
The following syntax rules apply:
vbin #i1: #i2 #r: Simplest command allowed. #i1: is the range in data channels over which the binning needs to take place. #i2 in the minimum amount of data channels that need to be binned, and #r is the minimal S/N ratio one wants the complete data set to have.
vbin #r1: #i #r2 unit #a: The same command as above, except that now the ranges over which the data is to be binned (#r1:) are specified in units (#a) different from data channels. These units can be eV, keV, Å, as well as in units of Rydberg (ryd), Joules (j), Hertz (hz) and nanometers (nm).
vbin [instrument #i1:] [region #i2:] #i3: #i4 #r: Here #i3: and #i4 are the same as #i1: and #i2 in the first command, also #r is the minimal S/N ratio required. However, here one can specify the instrument range #i1: and the region range #i2: as well, so that the binning only is performed for a certain data set.
vbin [instrument #i1:] [region #i2:] #r1: #i2 #r2 [unit #a]: This command is the same as the above, except that here one can specify the range over which the binning should occur in the units specified by #a. These units can be eV, Å, keV, as well as in units of Rydberg (ryd), Joules (j), Hertz (hz) and nanometers (nm).
vbin 1:10000 3 10: Bins the data channels 1:10000 with a minimal bin width of 3 data channels, and a minimum S/N ratio of 10.
vbin 1:4000 3 10 unit ev: Does the same as the above, but now the data range to be binned is given in eV, from 14000 eV, instead of in data channels.
vbin instrument 1 region 1 1:19 3 10 unit a: Bins the data from instrument 1 and region 1 between 1 and 19 Å with the same minimum bin width and S/N as above.