As of Mon May 20 22:46:11 2024

LTESS: Task do make linear combination mosaics


                                   Input image
INNAME                                Image name (name)
INCLASS                               Image name (class)
INSEQ              0.0      9999.0    Image name (seq. #)
INDISK                                Image disk drive #
                                   Output  image
OUTNAME                               Image name (name)
OUTCLASS                              Image name (class)
OUTSEQ            -1.0      9999.0    Image name (seq. #)
OUTDISK                               Image disk drive #

NMAPS              1.0      4087.0 Number of maps to analyse
NOISE    *         0.0             Image noise, units are
         *                         (Jy/BEAM)
BLC                0.0        4096 Bottom left corner of LTESS
TRC                0.0        4096 Top right corner of LTESS
PBSIZE                             PB FWHM in arcseconds:
                                   < 0 - no PB correction
                                   = 0 - use PBPARM
                                   > 0 - use Gaussian
PBPARM                             Beam parameters:
                                   (1) Cutoff 0 -> 0.07
                                   (2) > 0 -> Use (3)-(7)
                                   (3)-(7) Beam shape
BADDISK                            Disks to avoid for scratch.


Type: Task
Use:  LTESS is used to make a linear combination mosaic by correcting
      for the individual primary beam patterns and optimizing signal
      to noise.  The individual images must all be already placed on
      the desired output projective geometry including image size and
      reference pixel.
      NOTE: FLATN can also do this tesselation among other things and
      it takes care of the image geometry for you.
  INNAME......The input image name.      Standard defaults.
  INCLASS.....The input image class.     Standard defaults.
  INSEQ.......The input image seq. #.    0 => highest.
                 If NMAPS > 1 then images having sequence
                 numbers INSEQ,INSEQ+1,...,INSEQ+NMAPS-1 are
                 operated on.
  INDISK......The input image disk drive #. 0 => any.
  OUTNAME.....The LTESS image name.         Standard defaults.
  OUTCLASS....The LTESS image class.  Standard behavior with
              default = 'xLTESS' if INCLASS = 'xMAP', where x
                           is any character
                        'LTESS' if INCLASS = anything else
  OUTSEQ......The LTESS image seq. #.  0 => highest unique.
              If >0; image will be created if new,
              overwritten if image name exists.
  OUTDISK.....The LTESS disk drive no. 0 => highest with space
  NMAPS.......Number of maps to be combined. Must be in
              sequence starting at INSEQ.
  NOISE.......The estimated R.M.S. error for each image is
              NOISE (Jy/beam).
              NOISE(64) is used for fields > 64.
  BLC.........Bottom left corner of LTESS image, BLC(3) gives
              the channel number to combine.
  TRC.........Top right corner of image; both BLC and TRC
              default do that the inner quarter is chosen.
  PBSIZE......Size of primary beam in arcsec, FWHM of Gaussian model.
              One number per field.
              If = 0, use PBPARM beam with defaults suitable to the
              If < 0, do no primary beam correction, e.g. for fields
                      that are not interferometer data.
              If > 0, use a Gaussian of FWHM of PBSIZE(I).
              PBSIZE(64) is used for fields > 64.
  PBPARM......Primary beam parameters:
              (1) Lowest beam value to believe: 0 -> 0.07  Sources
                  outside this range are ignored.
              (2) > 0 => Use beam parameters from PBPARM(3)-PBPARM(7)
                  Otherwise use default parameters for the VLA (or
                  ATCA where appropriate)
              (3-7)..For all wavelengths, the beam is described by the
                   1.0 + X*PBPARM(3)/(10**3) + X*X*PBPARM(4)/(10**7) +
                   X*X*X*PBPARM(5)/(10**10) + X*X*X*X*PBPARM(6)/(10**13)
                where X is (distance from the pointing position in arc
                minutes times the frequency in GHz)**2.
                See explain for details
  BADDISK.....This array contains the numbers of disks on which
              it is desired that scratch files not be located.
              BADDISK has no effect on input and output maps.


LTESS :  Task which makes linear combination mosaics


LTESS is used to make linear combinations of up to 4087 input
images which must already reside on the same grid with the same
projection.  This can be arranged with HGEOM for example,
remembering to

LTESS was intended primarily to work on images produced by MEM-based
tasks VTESS and UTESS.  The references below apply to those tasks.


Cornwell T.J., and Evans K.F., "A simple Maximum Entropy
deconvolution algorithm", Astronomy and Astrophysics, (1985)

Burch,S.F, Gull,S.F., and Skilling,J., "Image restoration by a
powerful Maximum Entropy method", Computer Vision, Graphics and
Image processing, 23, 113-128 (1983).


Primary beam correction

     FACES corrects an image for the primary beam attenuation of
the antennas.  The function used to model the primary beam for normal
VLA frequencies

            F(x) =  1.0
                   + parm(3) * 10E-3  * x
                   + parm(4) * 10E-7  * x*x
                   + parm(5) * 10E-10 * x*x*x
                   + parm(6) * 10E-13 * x*x*x*x
                   + parm(7) * 10E-16 * x*x*x*x*x

where x is proportional to the square of the distance from the
pointing position in units of [arcmin * freq (GHz)]**2, and F(x)
is the multiplicative factor to divide into the image intensity at the
distance parameter x.  For other antennas, the user may read
in appropraite constants in PBPARM(3) through PBPARM(7).  The
flag, PBPARM(2) must be set to a positive number to invoke this
option and PBPARM(3) must not be zero.
     This correction scales with frequency and has a cutoff
beyond which the map values are set to an undefined pixel value GIVEN
in PBPARM(1).  At the VLA frequencies the default cutoff is
                 1.485 GHz     29.8  arcmin
                 4.885 GHz      9.13 arcmin
                15     GHz      2.95 arcmin
                22.5   GHz      1.97 arcmin
and occurs at a primary beam sensitivity of 2.3 percent of the value at
the beam center.  Corrections factors < 1 are forced to be 1.
The estimated error of the algorithm is about 0.02 in (1/F(x))
and thus leads to very large errors for x>1500, or at areas
outside of the primary response of 20 percent.  The cutoff level
may be specified with DPARM(1).

Default values of PBPARM for the VLA are given by Perley's fits:
      0.0738 GHz  -0.897  2.71   -0.242
      0.3275      -0.935  3.23   -0.378
      1.465       -1.343  6.579  -1.186
      4.885       -1.372  6.940  -1.309
      8.435       -1.306  6.253  -1.100
     14.965       -1.305  6.155  -1.030
     22.485       -1.417  7.332  -1.352
     43.315       -1.321  6.185  -0.983
For the ATCA, these are by default:
      1.5 GHz     -1.049   4.238  -0.8473  0.09073  -5.004E-3
      2.35        -0.9942  3.932  -0.7772  0.08239  -4.429E-3
      5.5         -1.075   4.651  -1.035   0.12274  -6.125E-3
      8.6         -0.9778  3.875  -0.8068  0.09414  -5.841E-3
     20.5         -0.9579  3.228  -0.3807  0.0       0.0
For the Karl G Jansky VLA ("EVLA"), the defaults are frequency
dependent.  If the observing frequency is between two tabulated
frequencies, then the beam is computed for each of the tabulated
frequencies and then interpolated to the observing frequency.  The
values used are far too numerous to give here, see EVLA Memo 195,
"Jansky Very Large Array Primary Beam Characteristics" by Rick Perley,
revision dated June 2016.  Obtain it from

                 RICK PERLEY'S (OLD) REPORT

	Polynomial Coefficients from LSq Fit to VLA Primary
	Beam raster scans.

	Functional form fitted:

		1 + G1.X^2 + G2.X^4 + G3.X^6

	where X = r.F,

	and 	r = radius in arcminutes
		F = frequency in GHz.

	Fits were made to 3 percent cutoff in power for 24 antennas.
Poor fits, and discrepant fits were discarded, and the most
consistent subset of antennas had their fitted coefficients
averaged to produce the following 'best' coefficients.

Freq.		G1		G2		G3

1.285           -1.329E-3       6.445E-7        -1.146E-10  *
1.465           -1.343          6.579           -1.186 "
4.885           -1.372          6.940           -1.309
8.435           -1.306          6.253           -1.100
14.965          -1.305          6.155           -1.030
22.485 (old)    -1.350          6.526           -1.090      *
22.485 (new)    -1.417          7.332           -1.352
43.315          -1.321          6.185           -0.983

	The estimated errors (from the scatter in the fitted
coefficients) are generally very small:

	G1: .003 at all bands except Q (.014)
	G2: .03 to .07 at all bands except Q (.15)
	G3: .01 to .02 at all bands except Q (.04)

	R. Perley  21/Nov/00

* The 1.285 and 22.485 old feed values are not used.