[daip] IMERG

[Lynn D. Matthews]

 	Eric,

I have placed four files in ftp at 
ftp://cfa-ftp.cfa.harvard.edu/outgoing/lmatthew/

These are:

VLA_orignal.fits (a deconvolved VLA channel image)

GBT_original.fits (GBT map channel image from cube made with SDGRD)

GBT_hgeom.fits (GBT channel map regridded to match VLA data using HGEOM)

GBT_hgeom_addbeam.fits (regridded GBT map with beam parameters added to 
header using "ADDBEAM").

As you'll see, there isn't much in the VLA image, although the little 
HI cloud at the center is astrophysically quite interesting.

Simply using COMB I can get a combined map that looks pretty good, but 
trying to do things "right" with IMERG, I can't get anything sensible.

Appended below is an example of inputs I tried (although I've tried many 
variations). The scaling factor the program computes essentially 
downweights th GBT data to nothing. If I force this to something more 
significant, then I see nothing but a series of concentric squares equal 
in size to the GBT map.

Perhaps my maps aren't of the type the program is expecting, but I've 
tried altering the GBT map units to Jy/beam, forcing the two images to 
have the same FOV, etc., all to no avail.

I have seen where CASA does indeed have tools to deal with this type of 
combination, although I don't have it installed and have no prior 
experience with even the rudiments of it, so that would be a major 
undertaking.

Lynn

AIPS 1: IMERG :  Task which merges high and low res. images
AIPS 1: Adverbs     Values                 Comments
AIPS 1: ----------------------------------------------------------------
AIPS 1:                                    High res. image
AIPS 1: INNAME     'VLA 70'                   Image name (name)
AIPS 1: INCLASS    'SUBIM'                    Image name (class)
AIPS 1: INSEQ         1                       Image name (seq. #)
AIPS 1: INDISK        4                       Image disk drive #
AIPS 1:                                    Low res. image
AIPS 1: IN2NAME    'GBT V=70 B'               Image name (name)
AIPS 1: IN2CLASS   'SUBIM'                    Image name (class)
AIPS 1: IN2SEQ        2                       Image name (seq. #)
AIPS 1: IN2DISK       4                       Image disk drive #
AIPS 1:                                    Output  image
AIPS 1: OUTNAME    'TEST'                     Image name (name)
AIPS 1: OUTCLASS   ' '                        Image name (class)
AIPS 1: OUTSEQ        0                       Image name (seq. #)
AIPS 1: OUTDISK       4                       Image disk drive #
AIPS 1:
AIPS 1: BLC         172         173        Bottom left corner of input
AIPS 1:            *rest 0
AIPS 1: TRC         340         341        Top right corner of input
AIPS 1:            *rest 0
AIPS 1: UVRANGE       0.17        0.46     Min and max baseline (klam.)
AIPS 1:                                    defining annulus of overlap
AIPS 1: FACTOR        0                    If > 0.0 , use as norm.
AIPS 1:                                    factor for low res. image
AIPS 1: AVOPTION   ' '                     Averaging option '  ','MEAN'
AIPS 1: DOWEIGHT     -1                    <= 0 => do not correct for
AIPS 1:                                    beams (BMAJ, BMIN, BPA)
AIPS 1: BADDISK    *all 0                  Disks to avoid for scratch.




On Sat, 20 Jun 2009, Eric Greisen wrote:

> Lynn D. Matthews wrote:
>> I have a GBT map that I've created using SDGRD and would now like to 
>> combine this with some VLA data. Is IMERG the appropriate task for this 
>> purpose?
>> 
>> So far, I've been unable to obtain anything useful from IMERG (e.g., I get 
>> something that looks similar to the original VLA map with some extra 
>> noise/negative flux in the region of the GBT map). This after regridding 
>> the GBT map to match the VLA pixel scale, adding the GBT beam size to the 
>> header, and converting the units to Jy/beam. I have done no corrections to 
>> the input (deconvolved) VLA map. Am I misunderstanding what the program 
>> wants in terms of the input maps?
>> 
>> Incidentally, I have noticed a minor bug, in that messages report the wrong 
>> INNAME for the "HI-RES MAP" (they instead report the INNAME of the "LO-RES 
>> MAP").
>> 
> There is a typo in the HI routine where it does a message about the files. 
> That is easily fixed - but I do not know this routine well.
>
> Perhaps you could send me your images and inputs and I will play with it a 
> bit to see if I can get anything useful.  I am not sold on this task although 
> something like this clearly needs to be done to merge the images.  There have 
> been bold claims about the equivalent task in aips++ - perhaps casa may have 
> it.
>
> Thanks,
>
> Eric
>