AIPS NRAO AIPS HELP file for SETFC in 31DEC18



As of Fri Jan 19 20:23:49 2018


SETFC: Task to make a BOXFILE for input to IMAGR

INPUTS

INNAME                             UV dataset name (name)
INCLASS                            UV dataset name (class)
INSEQ             0.0    9999.0    UV dataset name (seq. #)
INDISK            0.0       9.0    Disk drive #
SOURCES                            Source selected
BCOUNT           0.0      511.0    First field number to use
BOXFILE
                                   disk file to write to (the
                                   input BOXFILE for IMAGR)
CELLSIZE $      0.0                (X,Y) size of grid in asec
IMSIZE   $      0.0      16384     field size
SHIFT                              Position shift (RA,Dec) asec
                                   for all fields
FLUX                               Minimum component flux =
                                   (source * beam)
BPARM                              (1) Inner region radius (deg)
                                   (2) Field overlap (pixels)
                                   (3) Factor to scale NVSS
                                       fluxes, 0 -> 1
                                   (4) Radius NVSS search (deg)
                                   (5) Flux limit in NVSS (Jy)
                                   (6) IMSIZE for NVSS fields
                                   (7) IMSIZE for Sun fields
                                   (8) Write Clean boxes for
                                       NVSS fields
                                   (9) Maximum allowed phase
                                       error in imaging
                                   (10) Points per beam
OPTYPE                             'USEF' -> use F type field
                                   cards rather than C type
PBPARM                             Beam parameters:
                                   (1) Cutoff; (2) Use (3)-(7)
                                   (3)-(7) Beam shape parms
INLIST
                                   NVSS input file name
                                   ' ' => AIPS provided.
NFIELD   @                         Number fields found

HELP SECTION

SETFC
Type:  Task
Use:   SETFC makes an output BOXFILE to be used as input to IMAGR.  It
       is meant to be used in preparation for wide-field 3D imaging.
       It prepares BOXFILE data to image an area around the pointing
       position using a number of overlapped fields.  Optionally, it
       also searches through lists of sources from the NVSS (21 cm VLA
       D-array) or WENSS/WISH (92 cm Westerbork northern and southern)
       surveys and adds outlier fields to image those sources above a
       specified flux limit.  It writes an inscribed circular Clean
       box for the fields covering the primary beam and can,
       optionally, write small Clean boxes for each of the sources in
       the outlier fields.  The latter will almost certainly require
       later hand editing but they are instructive.

       NOTE: if you do not need the BOXFILE, the task will use a blank
       BOXFILE as indication that the BOXFILE output should go to the
       message terminal instead.
Input adverbs:
  INNAME......The UV dataset name (name).    Standard defaults.
  INCLASS.....The UV dataset name (class).   Standard defaults.
  INSEQ.......The UV dataset name (seq. #).  0 => highest.
  INDISK......The disk drive #.         0 => any.
  SOURCES.....The source to be used from a multi-source file; a single
              source name is required to get the central pointing
              position from the source table.  Ignored for single-source
              files.
  BCOUNT......First field number to use.  0 -> 1.  This allows you to
              append to a pre-existing file with lower field numbers
              obtained in some other way.
  BOXFILE.....Output text file containing lines which specify the fields
              for the multi-field imaging.  This file should then be
              specified as the BOXFILE for IMAGR.  If the file already
              exists, the new information will be appended to it.
              If BOXFILE = ' ', the output will be redirected to the
              message terminal/file.  The field cards will be at
              message level 4, the clean box cards at message level 2.
  CELLSIZE....Pixel size for the fields in IMAGR in arc seconds.
              Value used is returned (i.e. 0's are changed to
              recommended values)
  IMSIZE......Size of each field.  Value used is returned (i.e. 0's
              are changed to recommended values)
              If CELLSIZE and/or IMSIZE are zero, the data are read to
              find the maximum baseline and maximum W in order to
              estimate these parameters.  The "maximum phase error" in
              gridding ignoring the W term may be controlled with
              BPARM(9).
  SHIFT.......Specifies a position shift in arc seconds at the phase
              center for all of the fields in the inner portion.  The
              output RA = RA0 + SHIFT(1)/cos(DEC0) and DEC = DEC0 +
              SHIFT(2) where 0 refers to the input coordinates.
  FLUX........Minimum included component "flux" = source flux times
              the single-dish beam power.  0 => any in INLIST meeting
              BPARM(4).  Note, the single dish beam power is taken to
              be 0.01 outside the main lobe.  Fluxes are read from the
              table, scaled by BPARM(3), and then compared to FLUX.
  BPARM.......(1) The radius in degrees to be covered fully by
                  overlapping fields.  <= 0 means do not do fly's eye
                  list of fields.  < 0 => do not include catalog sources
                  within abs (BPARM(1)) of the origin.
              (2) Field overlap in pixels 0 -> 5.  The program now
                  takes into account that the Cleaning area is smaller
                  than the image size since the outer 6 pixels are
                  regarded as unreliable.
              (3) Factor to scale NVSS fluxes (to account for spectral
                  index on average).  0 -> 1
              (4) Radius for the search in the catalog for interfering
                  sources.   < BPARM(1) => no search.  Try 30 for 74
                  Mhz imaging.  All sources outside the center of the
                  outermost fly's eye field (n.b. < BPARM(1)) and
                  < BPARM(4) are included if they meet the flux
                  criteria.
              (5) Flux (Jy) limit in catalog search,  There are 4
                  AIPS-provided NVSS files each containing sources > its
                  flux limit.  Those limits are 50, 100, 300, and 1000
                  mJy and searches will be faster if you are just above
                  rather than just below one of these limits.
              (6) Desired size of external fields; 0 -> 128.
              (7) Desired size of external fields on Sun; 0 -> 256.
              (8) > 0 => write Clean boxes in outlier fields.  If > 5,
                  use BPARM(8) for the radius in cells.
              (9) The phase error made in gridding a point is approx
                  180 * W * (l*l + m*m) degrees where W is in
                  wavelengths and l and m in radians.  Thus the
                  maximum field of view (radius) is
                         sqrt(E/(180*Wmax)).
                  BPARM(9) gives the allowed value of E in degrees,
                  where BPARM(9) = 0 -> 45 degrees.  The actual value
                  of E used will be reduced by the cos (zenith angle)
                  and will be reduced still further if the average
                  abs(W) > Wmax/4 or the sqrt (average W*W) > Wmax/3.
              (10) The cell size recommended is 1 / Bmax / Nppb where
                  Bmax is tha maximum baseline and Nppb is the number
                  of points per beam.  Even with uniform weighting the
                  beam is often larger than 1/Bmax so one may end up
                  with more than Nppb points per beam.  BPARM(10) sets
                  points per beam (when CELLSIZE=0) and 0 -> 3.
  OPTYPE......'USEF' -> use F type field cards giving the RAshift and
                        DECshift of the center of the field (facet)
                        This can be used for more than one pointing
                        although the NVSS sources and Sun will not be
                        correct.
              other  -> use C type field cards giving the center RA
                        and DEC for each field
  PBPARM......Primary beam parameters:
              (1) Lowest beam value to believe: No default.
                    0.0 => use any beam value
              (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
                function:
                   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)
                   X*X*X*X*X*PBPARM(7)/(10**16)
                where X is (distance from the pointing position in arc
                minutes times the frequency in GHz)**2.
                See explain for details
  INLIST......Catalog input file name.  For format see Explain
              ' ' => an AIPS-provided files appropriate to BPARM(5):
              Epoch 2000:
                FLUX >= 1.000  NV00.1000  (  2267 objects)
                FLUX >= 0.300  NV00.0300  ( 14456 objects)
                FLUX >= 0.100  NV00.0100  ( 63411 objects)
                FLUX >= 0.030  NV00.0030  (237600 objects)
              Epoch 1950:
                FLUX >= 1.000  NV50.1000  (  2267 objects)
                FLUX >= 0.300  NV50.0300  ( 14456 objects)
                FLUX >= 0.100  NV50.0100  ( 63411 objects)
                FLUX >= 0.030  NV50.0030  (237600 objects)
              The WENSS/WISH surveys ar also available $AIPSTARS as
                FLUX >= 0.100  WE00.0100  ( 99709 object 2000)
                FLUX >= 0.100  WE50.0100  ( 99709 object 1950)
              Some sites may choose to download really large source
              lists to deeper flux levels.  These may include from the
              NVSS survey:
                FLUX >= 0.003  NV00.0003  (1560007 objects, 2000)
                FLUX >= 0.003  NV50.0003  (1560007 objects, 1950)
              and the WENSS/WISH survey:
                FLUX >~ 0.010  WE00.0000  (319770 objects, 2000)
                FLUX >~ 0.010  WE50.0000  (319770 objects, 1950)
              These deep files may be particularly useful for BOXES
              but are too deep to be of much use here.
              Note: the WENSS survey covers +90 to +28 degrees
              declination and the WISH survey covers -25 to -15 with
              some sources to -9.
Output adverbs (returned to AIPS):
  CELLSIZE....Pixel size for the fields in IMAGR in arc seconds.
              Value used is returned (i.e. 0's are changed to
              recommended values)
  IMSIZE......Size of each field.  Value used is returned (i.e. 0's
              are changed to recommended values)
  NFIELD......Number of fields put in the bOXFILE.

EXPLAIN SECTION

SETFC:  Task to make an input BOXFILE to be used with IMAGR
DOCUMENTOR:  Bryan Butler (NRAO)

                        DESCRIPTION

This task was motivated by Lazio & Kassim's SETFAC RUN file which sets
facets for wide-field imaging via IMAGR.  The original version of the
task was then written by Bryan Butler.

The purpose of the task is to set up a BOXFILE for input to IMAGR.  This
is intended to be used for wide-field imaging applications (e.g., VLA 74
MHz data), as a way of specifying multiple fields which cover a wide
field of view.  It is quite usefull at any wavelength however.

The task, if instructed to determine cell and/or image size, will read
the UV data to find the maximum baseline and maximum W.  The cell size
in radians is then 1/Bmax / Nppb where Nppb is the number of points
per beam.  The formula for phase error which determines the maximum
radius of a facet comes from Thompson, Moran, and Swenson,
"Interferometry and Synthesis in Radio Astronomy" 2001, pages 73-74.
In radians, the facet radius for which all phase errors are less than
E degrees is sqrt (E / Wmax / 180).

It is found that an error as great as 45 degrees is okay if there are
not too many points at large W and if the elevation is not too low.
The user may control E with BPARM(9) but the E actually used is set
by E = BPARM(9) * cos (ZA) * Wmax / max (Wmax, 4*Wa, 3*Wr)
where ZA is the zenith angle at transit, Wa is the average abs(W),
and Wr = sqrt (average W*W).  This biases things when more than a few
points are at large W and reduces the allowed error at low elevations
where the results of the phase errors are more serious.

The task is split into 2 relatively independent parts.  The first is the
creation of a "fly's eye" - a tiling of overlapping fields which cover
the central part of the primary beam.  The second part is the creation
of several smaller fields which are centered on NVSS sources and the
Sun.  The two parts are independent, i.e., you can do either or both of
them on any particular run of SETFC.

The fly's eye tiling is controlled by the parameters BPARM(1), BPARM(2),
CELLSIZE, IMSIZE, and SHIFT.  See their description above...

The NVSS source catalog is searched within some search radius for
sources with flux density greater than specified, and small fields are
created around these sources.  In order to do this, the position (RA,
DEC) of the pointing phase center is required.  This is obtained from
the input UV data set.  In the case of a single-source data set, it is
read from the header.  In the case of a multi-source data set, the
source must be specified in the first element of the adverb SOURCES, and
the position is read from the SU extension.  The selection of sources is
controlled by the adverbs BPARM(4), BPARM(5)< BPARM(6).  See their
description above.   The source catalog may be specified in INLIST or
you may use one of the AIPS-provided versions of the NVSS.  The format
of the file is:

All lines beginning with a semi-colon are ignored.  They are the
copyleft, a descriptive text in the AIPS files, and other comments.
Be careful about the epoch of the coordinates.

Remaining give the Right ascension in degrees, Declination in degrees,
Flux in mJy, and optionally a FWHM in arc seconds using format
F9.5,1X,F9.5,I7,F10.4.  A sample is given below no width is shown
since none are used by SETFC.

  0.08521  55.65239   1518
  0.22108  40.90052   1301
  0.84166 -17.45316   2415
  1.23802  12.80524   1071
  1.37727  69.39949   1105
  1.55780  -6.39310   2051
  1.59416  -0.07363   3898
  2.12217  -5.97935   1323
358.54728  32.91998   1183
358.59049  45.88455   1873
358.78961  49.83570   2306
358.97312  15.69069   1104
359.25280 -34.75882   1286
359.32748  14.76875   1020
359.38022 -11.42748   1814
359.64781  44.07789   1940


PRIMARY BEAM PARAMETERS

     SETFC 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
http://library.nrao.edu/evla.shtml


                 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

0.0738          -0.897E-3       2.71 E-7        -0.242E-10
0.3275          -0.935          3.23            -0.378
1.285           -1.329          6.445           -1.146      *
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.

AIPS