Dealing with DAS spectra: basics

As described elsewhere, DAS spectra usually consist of several overlapping (in frequency/velocity space) sections (or `sub-bands'). Except for single sub-band (125-MHz) spectra it is necessary to combine these sub-bands to produce a nice spectrum. This is done with the command das-merge; e.g.:

$>\!>$ r-g-d 131; das-merge

This command removes the large data values at the ends of the subbands, and combines the subbands into one continuous spectum. It is sufficient to take the defaults for most purposes; however, see Section  for caveats etc. The final spectrum should be free of evidence of sub-band edges, except in pathological cases.

Note that:

• It is not necessary to do the das-merge operation on individual spectra before averaging; the average can be formed first and das-merge applied to the result.
• If you have modified the centre frequency of the previous spectrum using the s-l-r-f command³ it is necessary to reset the defaults using

  $>\!>$ s-l-r-f 0.0

  before attempting the das-merge command.