[daip] FLATN and primary beam correction

[Andy Biggs]

Hi. I'm using FLATN to combine 4 separate GMRT 610-MHz pointings together. It is generally acting sensibly, but there is a strange pattern around the main area of interest that I don't think should be there. Please see attached figure. Note that each pointing is very large and should be greatly truncated by FLATN i.e. the pixels with the holes in the centre probably correspond to real data.

I am using the recommended parameters for the GMRT beam and I thought at first that the problem might be due to the GMRT polynomial increasing back above my cutoff of 0.1 at large distances. However, I just tried it again with PBPARM(6)=0 and that shows the same problem.

Are my inputs okay?

AIPS 1: FLATN: Re-grid multiple fields and pointings to one image
AIPS 1: Adverbs     Values                 Comments
AIPS 1: ----------------------------------------------------------------
AIPS 1:                                    Input images
AIPS 1: INNAME     'GROTH'                    Image name (name)
AIPS 1: INCLASS    'ICL001'                   Image name (class)
AIPS 1: INSEQ         1                       Image name (seq. #)
AIPS 1:                                          (specify)
AIPS 1: INDISK        1                       Image disk drive #
AIPS 1: NFIELD       85                    Max number of fields per
AIPS 1:                                       pointing
AIPS 1: NMAPS         4                    Number of pointings
AIPS 1:                                    Output image
AIPS 1: OUTNAME    ' '                        Image name (name)
AIPS 1: OUTCLASS   ' '                        Image name (class)
AIPS 1: OUTSEQ        0                       Image name (seq. #)
AIPS 1: OUTDISK       1                       Image disk drive #
AIPS 1: IMSIZE     12000       12000       Output image size in pixels
AIPS 1: COORDINA     14          22        Central pixel coordinate
AIPS 1:              32.402      53        all 0 => use observed
AIPS 1:              17          11
AIPS 1: COOTYPE    ' '                     Desired projection type
AIPS 1: COOINC        0           0        Desired coordinate increment
AIPS 1: COOREF        0           0        Desired reference pixel
AIPS 1: ROTATE        0                    Rotation to be used (deg)
AIPS 1: REWEIGHT      0           0        (1) Interpolation halfwidth
AIPS 1:                                    (2) Minimum fraction of good
AIPS 1:                                        pixels required (0->1/3)
AIPS 1: WEIGHTIT      0                    Weight image down by WEIGHTIT
AIPS 1:                                    times radius from center in "
AIPS 1: EDGSKP        5                    Skip pixels around the edges
AIPS 1:                                    inscribed ellipse also used
AIPS 1: OPTYPE     ' '                     For mosaics only (NMAPS>1)
AIPS 1:                                    compute and output expected
AIPS 1:                                    noise ('NOIS') or weight
AIPS 1:                                    ('WEIG').
AIPS 1: APARM      *all 0                  (1) >0 => do 3-D corr.
AIPS 1:                                       ONLY for snapshots
AIPS 1:                                    (2) Parallactic angle (deg)
AIPS 1:                                    (3) Zenith angle (deg)
AIPS 1:                                    (4-8) radial scaling parms
AIPS 1:                                    (9) Linear scaling
AIPS 1: PBPARM        0.1         1        Beam parameters (NMAPS > 1)
AIPS 1:              -3.486      47.749    (1) Cutoff; (2) Use (3)-(7)
AIPS 1:             -35.203      10.399    (3)-(7) Beam shape
AIPS 1:               0
AIPS 1: NOISE      *all 0                  Relative uncertainties by
AIPS 1:                                    pointing: 0 -> image header
AIPS 1: BADDISK    *all 0                  Disks to avoid for scratch

Thanks,

Andy
-------------- next part --------------
A non-text attachment was scrubbed...
Name: flatn.png
Type: image/png
Size: 1418628 bytes
Desc: flatn.png
URL: <http://listmgr.nrao.edu/pipermail/daip/attachments/20120116/923778d0/attachment.png>