Selecting Spectral Windows and Channels

Oftentimes, you don't want to run a certain task on every single spectral channel in your data. This is where the 'spw' parameter comes in; it allows you to select both spectral windows and channels. A colon separates spectral window information from channel information, and a tilde denotes a range. NOTE: all index numbering in CASA begins with 0, not 1!

Here are some basic examples:

spw = '1'                                 # Spectral window 1 
spw = '0~3'                               # Spectral windows 0, 1, 2, and 3
spw = '1,3,5'                             # Spectral windows 1, 3, and 5
spw = '*:10~50'                           # Channels 10--50 for all spectral windows

You can also use frequency units to select spectral windows or channels:

spw = '1412~1415MHz'                      # All spectral windows containing 1412--1415 MHz
spw = '*:1412~1415MHz'                    # Channels in the range 1412--1415 MHz

It is also possible to specify multiple ranges:

spw = '0:3~10, 1:20~30'                   # Channels 3--10 from spectral window 0 and channels 20--30 from spectral window 1 

You can find more detail in the CASA cookbook.

--Laura Chomiuk 21:52, 10 February 2010 (UTC)