[daip] Re: MOMNT questions

[Eric Greisen]

Veera Boonyasait writes:

I am unfamiliar with MOMNT in any detail - I did not write it and have
only reluctantly worked on it occasionally.  REading the code however,
I think I can answer your questions

 >    There are a few questions I have in regards to the task MOMNT 
 > in the original AIPS. I am trying to calculate the amount of 
 > RMS noise level contribution to the surface density map generated
 > by the task. Typically, I use the OPTYPE 'HG' with CELLSIZE= 3,2.
 > What I would like to ask is if MOMNT applies only the FLUX cutoff
 > method or does it also incorporate the window method as well? If
 > not, how does the task recognize one-channel noise spikes? The
 > EXPLAIN file does not describe whether a signal must be contiguous 
 > for a number of channels before being integrated. I see that the 

    There is no windowing - simply the flux cutoffs applied to the
smoothed image.  A one-channel spike would be summed into the
moments.

 > function moments in aips++ has the window method but I have been 
 > reluctant to use the program (aips++) because the version we have 
 > has been very reluctant in reading some of my FITS files which are 
 > easily recognized by AIPS. 

     The aips++ package has many problems and I would not want to
depend on it - particularly in an area that may never have been used
to actually produce science.

 > 
 > Lastly, the Gaussian kernel that is specified is a bit unclear to 
 > me. If the original beamsize of my data is 20", then does MOMNT 
 > convolve the data cube with a 40" beam to make the mask?
 > 
C                                 SPATIAL GAUSS
      NXY = MIN(((IROUND(GSIG)*2)/2)*2+1, 11)
      NXY2 = NXY/2+1
      Z = -4.0*LOG(2.0)/(GSIG*GSIG)
      S = 0.0
      DO 20 I=1,NXY
         X = NXY2-I
         KXY(I) = EXP(X*X*Z)
         S = S + KXY(I)
 20      CONTINUE

where I is in pixels.  The GSIG is the full width at half maximum in
pixels, not something related to arc seconds wrt the Clean beam size
or some such.

Eric Greisen