Channel selection in the spw parameter

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2.3.3.1 Channel selection in the spw parameter

ALERT!

Not all options are available yet, such as percentages or velocities. Stay tuned!

Channel selection can be included in the spw string in the form ’SPWSEL:CHANSEL’ where CHANSEL is the channel selector. In the end, the spectral selection within a given spectral window comes down to the selection of specific channels. We provide a number of shorthand selection options for this. These CHANSEL options include:

Channel ranges: ’START~STOP’
Frequency ranges: ’FSTART~FSTOP’
Velocity ranges: ’VSTART~VSTOP’ (not yet available)
Bandwidth percentages: ’PSTART~PSTOP’ or ’PWIDTH’ (not yet available)
Channel striding/stepping: ’START~STOP^STEP’ or ’FSTART~FSTOP^FSTEP’

The most common selection is via channel ranges ’START~STOP’ or frequency ranges ’FSTART~FSTOP’:

spw = ’0:13~53’ # spw 0, channels 13-53, inclusive
spw = ’0:1413~1414MHz’ # spw 0, 1413-1414MHz section only

All ranges are inclusive, with the channel given by, or containing the frequency or velocity given by, START and STOP plus all channels between included in the selection. You can also select the spectral window via frequency ranges ’FSTART~FSTOP’, as described above:

spw = ’1413~1414MHz:1413~1414MHz’ # channels falling within 1413~1414MHz
spw = ’*:1413~1414MHz’ # does the same thing

You can also specify multiple spectral window or channel ranges, e.g.

  spw = ’2:16, 3:32~34’       # spw 2, channel 16 plus spw 3 channels 32-34
  spw = ’2:1~3;57~63’         # spw 2, channels 1-3 and 57-63
  spw = ’1~3:10~20’           # spw 1-3, channels 10-20
  spw = ’*:4~56’              # all spw, channels 4-56

Note the use of the wildcard in the last example.

A step can be also be included using ’^STEP’ as a postfix:

  spw = ’0:10~100^2’          # chans 10,12,14,...,100 of spw 0
  spw = ’:^4’                 # chans 0,4,8,... of all spw
  spw = ’:100~150GHz^10GHz’   # closest chans to 100,110,...,150GHz

A step in frequency or velocity will pick the channel in which that frequency or velocity falls, or the nearest channel.

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